Nutrients: Ingestion to Energy Metabolism 25

© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE ORcHAPteR DISTRIBUTION 2 NOT FOR SALE OR DISTRIBUTION © likk/ iStockphoto © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT nutrients: FOR SALE OR DISTRIBUTION ingestionNOT to FOR energySALE OR DISTRIBUTION Metabolism © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR Key DISTRIBUTION Questions addressed NOT FOR SALE OR DISTRIBUTION 1. What happens to nutrients after they are ingested? 2. How are carbohydrates digested, absorbed, transported, and assimilated in the body? 3. How are© fatsJones digested, & Bartlett absorbed, Learning, transported, LLCand assimilated in the body? © Jones & Bartlett Learning, LLC 4. How areNOT proteins FOR digested, SALE absorbed, OR DISTRIBUTION transported, and assimilated in the body?NOT FOR SALE OR DISTRIBUTION 5. How are minerals, vitamins, and water absorbed and transported in the body? 6. What is energy metabolism, and why is it important? © Jones7. What& Bartlett is energy? Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR8. What SALE is the OR human DISTRIBUTION body’s source of chemical energy? NOT FOR SALE OR DISTRIBUTION 9. How do cells make AtP? 10. What are the three energy systems? © Jones & Bartlett11. Learning, How do the LLC energy systems work together© toJones supply AtP& Bartlett during athletic Learning, performance? LLC NOT FOR SALE OR12. DISTRIBUTION What metabolic pathways are involved withNOT the FOR energy SALE systems? OR DISTRIBUTION

You are the Nutrition Coach Kay is an aspiring© Jones 800-meter & Bartlett track athlete Learning, who has LLC read various nutrition books© with Jones the hope & Bartlett of Learning, LLC finding theNOT ideal dietFOR for SALEher sport. OR From DISTRIBUTION her reading, she has learned that fats yieldNOT more FOR calories SALE OR DISTRIBUTION per gram than carbohydrates. in addition, she knows that dietary proteins are needed to help her muscles recover from training and additionally can be used for energy. She is now convinced that one of the popular high-fat, high-protein, low-carbohydrate diets is her best choice. Her coach dis- agrees with her decision. She recommends that Kay speak with a sports nutrition professional before © Joneschanging & Bartlett her current Learning, diet, in which LLC the majority of calories come© Jonesfrom carbohydrates. & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Questions • Bioenergetically speaking, is Kay on the right track with her thinking? • What energy system does an athlete running the 800-meter event rely on for energy? © Jones & Bartlett Learning,• is a diet of energy-denseLLC fats really better© for Jones Kay’s event? & Bartlett Learning, LLC NOT FOR SALE OR• DISTRIBUTION How would you explain to Kay why she shouldNOT orFOR should SALE not follow OR thisDISTRIBUTION new diet? © Shutterstock / fractal-an © Shutterstock

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What are the functions of the various parts of © JonesWhat & Bartlett happens Learning, to nutrients LLC after they are © Jones & Bartlett Learning, LLC the digestive system? ingested? NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION The anatomical organization and functions of the various When nutrients are ingested they have not technically parts of the digestive tract are shown in Figure 2.2 . The entered the body. The digestive tract is merely an inter- digestive system extends from the mouth to the anus and nalized conduit that connects the mouth to the anus (see is more than 25 feet long in most individuals. The mouth, Figure 2.1 ). Substances in the digestive tract are techni- or oral cavity, is the entry point for ingested nutrients. cally still outside of the© body Jones until & they Bartlett are absorbed Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTIONThe main digestive process NOTthat occurs FOR in SALE the mouth OR DISTRIBUTIONis across the membrane linings of this system. Once mastication, more commonly known as “chewing.” absorbed across the membranes of the digestive tract, The mechanical process of mastication breaks foods into the nutrients have officially entered the body and can be pieces, thereby increasing the exposed surface area of the transported via blood and lymph throughout the body. food and facilitating Because most foods are too large to be absorbed, they first © Jones & Bartlett Learning, LLC oral cavity ©Another Jones name & for Bartlett the enzymatic Learning, action.LLC must be broken down into smaller pieces via digestion. Three pairs of DigestionNOT is FOR the process SALE ofOR breaking DISTRIBUTION down ingested mouth, whichNOT makes FOR up the SALE first OR DISTRIBUTION segment of the gastrointestinal tract. salivary glands, food through mechanical and enzymatic activity so that namely the parotid, it can be absorbed into the body. The remainder of this submandibular, and mastication The process of section will discuss sublingual glands, digestion The process of break- the various parts of chewing. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLCsecrete saliva into ing down ingested foods into the gastrointestinal the oral cavity (see NOT FOR SALE OR DISTRIBUTION NOT salivaryFOR SALE glands ORGlands DISTRIBUTION of the their basic units in preparation system and their Figure 2.3 ). The saliva mouth that produce and secrete for absorption by the cells of the function in nutrient not only moistens saliva. gastrointestinal tract. digestion and the food particles, absorption. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Anatomical Functional organization organization Salivary Mouth glands Mouth Ingestion and © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning,digestion LLC Esophagus NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Liver Esophagus

Stomach Stomach Digestion © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC and NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTIONSmall absorption Gallbladder Pancreas intestine

Large Absorption intestine and elimination Rectum Elimination © Jones & BartlettSmall Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALEintestine OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

Liver These organs Large Gallbladder produce and secrete intestine Bile duct © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning,substances LLC that Pancreas aid in digestion. NOT FOR SALE OR DISTRIBUTION NOT FOR SALE SmallOR DISTRIBUTION intestine Rectum Figure 2.2 Functional organization of the digestive system. Although Anus © Jones & Bartlett Learning, LLC © Jonesdigestion & beginsBartlett in the Learning, mouth, most LLC digestion occurs in Figure 2.1 the stomach and small intestine. Absorption occurs pri- NOT FOR AnatomySALE OR of the DISTRIBUTION digestive system. NOTmarily FOR in SALEthe small OR intestine. DISTRIBUTION

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The small intes- © Jones & Bartlett Learning, LLC © Jonessmall & Bartlett intestine Learning,The portion ofLLC tine makes up the NOT FOR SALE OR DISTRIBUTION NOT FORthe SALE gastrointestinal OR DISTRIBUTION system where majority of the the bulk of digestion and absorp- length of the GI tract tion occurs. The small intestine is and is approximately divided into three segments: duo- 20 feet long. It is denum, jejunum, and ileum. divided into three Parotid © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC gland segments: the duo- NOT FOR SALE OR DISTRIBUTIONdenum, the jejunum, andNOT the FORileum SALE(see Figure OR 2.4 DISTRIBUTION). As Sublingual the partially digested food exits the stomach, it enters gland the duodenum, which is a short segment of the small intestine. Although approximately only a foot in length, © SubmandibularJones & Bartlett Learning, LLC the duodenum© Jones is where & Bartlett the food Learning, from the stomachLLC is gland barraged with more digestive enzymes from the gallblad- NOT FOR SALE OR DISTRIBUTION der and NOTpancreas. FOR Much SALE of the OR digestion DISTRIBUTION of foodstuffs is completed in the duodenum, making the food ready for absorption. In addition to the small intestine being long, the walls Figure 2.3 inside it are convoluted and lined with villi, which are © Jones &The Bartlett salivary glands. Learning, The three LLC pairs of salivary glands © Jones & Bartlett Learning, LLC small tube-shaped supply saliva, which moistens and lubricates food. Saliva NOT FOR SALE OR DISTRIBUTION NOT FORvilli SALESmall rod-shaped OR DISTRIBUTION projections projections (see also contains salivary enzymes that begin the digestion that cover the walls of the small Figure 2.5 ). Each vil- of starch. intestine. lus has blood and lymphatic supply so © Jones & Bartlett Learning, LLCthat absorbed nutrients can© Jones gain easy & accessBartlett into Learning, the cir- LLC culatory systems of the body. The combination of the NOT FOR SALE OR DISTRIBUTIONsmall intestine’s lengthNOT and the FOR convoluted SALE OR villi-lined DISTRIBUTION but also contains enzymes that initiate the enzymatic interior results in a large surface area with which to breakdown of carbohydrates and fats. absorb foodstuff. In fact, most of the absorption of nutri- The bolus of food is then swallowed and passes into ents occurs in the remaining segments of the small intes- the esophagus© Jones, &which Bartlett is a tube Learning, leading from LLC the back of tine: the© jejunum Jones and & Bartlettileum. Learning, LLC From the small intestine, the remainder of the undi- the oralNOT cavity FOR to SALEthe stomach OR DISTRIBUTION. Food passes so quickly NOT FOR SALE OR DISTRIBUTION through the esophagus that relatively little digestion gested, partially digested, and unabsorbed contents occurs there. Once in pass into the large intestine. The large intestine includes the colon (ascending, transverse, and descending), the esophagus The segment of the the stomach, the food is subjected to rectum, and the anal digestive system that connects the large intestine The terminal por- stomach acids and canal, which exits © Jones & oralBartlett cavity to theLearning, stomach. LLC © Jonestion & Bartlettof the gastrointestinal Learning, tract, LLC other enzymes that the body at the anus which receives undigested, partially NOT FOR SALEstomach ORThe DISTRIBUTIONdistensible, pouch- further the digestiveNOT FOR SALE OR DISTRIBUTION(see Figure 2.6 ). Pas- digested, and unabsorbed contents like portion of the gastrointestinal process. The stom- sage of the intesti- from the small intestine. It is in the system that receives foods from ach has a muscular nal contents along large intestine that the formation the esophagus. It has muscular wall that churns the the GI tract slows in of feces occurs. The large intestine walls that mechanically churn food food, mixing it with the large intestine, © Jones & Bartlett Learning, LLCconsists of the colon, rectum,© Jonesand & Bartlett Learning, LLC and assist in the digestive process. stomach acids and normally taking 18 anal canal. Ingested foods pass fromNOT the stom FOR- SALEenzymes. OR This DISTRIBUTION diges- NOT FORto SALE 24 hours OR to DISTRIBUTION pass ach into the duodenum. tive process contin- through. The intesti- ues for roughly an nal contents are subjected to bacteria that not only con- gastrointestinal tract (GI hour before food tinue digesting some of the undigested and unabsorbed tract) The regions of the digestive begins to exit the foodstuffs, but also produce intestinal gas and certain system© Jones that include & Bartlett the stomach, Learning, LLC vitamins.© SomeJones of the& Bartlett vitamins Learning,produced by LLC these bac- NOT FOR SALE OR DISTRIBUTIONstomach. Although NOT FOR SALE OR DISTRIBUTION small intestine, and large intestine. some absorption of teria are absorbed along with excess water as the nutrients does occur remaining contents pass through the colon. Water in the stomach, the overwhelming majority occurs in the absorption in the colon helps to solidify the remaining next portion of the gastrointestinal tract (GI tract), the excrement, which by the time it reaches the rectum is 60% solid matter and 40% water. The rectum is basically © Jones &small Bartlett intestine Learning,. LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

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© Jones & Bartlett Learning, LLC The liver secretes © Jones & Bartlett Learning, LLC Bile from bile which aids in NOT FOR SALE OR DISTRIBUTIONgallbladder the digestion of NOT FOR SALE OR DISTRIBUTION emulsifies fats. fats.

© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Pancreas secretes bicarbonate (a base) and enzymes that digest fats, carbohydrates, Duodenum and proteins. © Jones & Bartlett25–30 Learning, cm (10–12 in.) LLC © Jones & Bartlett Learning, LLC

NOT FOR SALE ORMost DISTRIBUTION digestion NOT FOR SALE OR DISTRIBUTION happens here. Secretions from liver, pancreas and gallbladder enter small intestine. Jejunum © Jones & Bartlett Learning, LLC~213 cm (~7 ft) © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Absorbs digested nutrients.

Absorbs digested nutrients. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Figure 2.4 The small intestine. Secretions from the pancreas, liver, and gallbladder assist in digestion. All along the intestinal walls, nutrients are absorbed into blood and lymph. Undigested materials are passed on to the large © Jones & Bartlett Learning,intestine. LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

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Capillary Lacteal Epithelial © Jones & Bartlett Learning, LLC cell © JonesHow & Bartlett are carbohydrates Learning, LLC digested, NOT FOR SALE OR DISTRIBUTION NOT FORabsorbed, SALE OR transported, DISTRIBUTION and assimilated in the body? Many different types of carbohydrates are found in foods. The commonality regarding the different types of © Jones & Bartlett Learning, LLCcarbohydrates is that they© Jones are all composed& Bartlett of Learning, simple LLC NOT FOR SALE OR DISTRIBUTIONsugars known as monosaccharidesNOT FOR. SALECarbohydrates OR DISTRIBUTION are classified based on the number of simple sugars making up their structure. For example, disaccharides are made up of two linked simple sugars. Oligosaccharides are carbohydrates composed of 3 to 10 linked sugars, and © Jones & Bartlett Learning, LLC polysaccharides© Jones are & complex Bartlett carbohydrates Learning, madeLLC of 11 NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTIONor more linked sim- monosaccharide A single sugar ple sugars. The Artery Vein Lymphatic vessel molecule. Monosaccharides are monosaccharide the building blocks for more com- most important to Figure 2.5 plex carbohydrates. the human body is The absorptive surface of the small intestine. To maximize glucose. To obtain © Jones &the Bartlett absorptive Learning, surface area, LLC the small intestine is folded© Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FORdisaccharide SALE ORA simple DISTRIBUTION carbohy- glucose from and lined with villi. You have a surface area the size of a drate that consists of two linked ingested foods, the tennis court packed into your gut. sugar molecules. carbohydrates must undergo digestion. oligosaccharide A complex car- The digestive pro- © Jones & Bartlett Learning, LLCbohydrate made up of 3 to 10© linked Jones cess& Bartlett breaks Learning, down LLC simple sugars. NOT FOR SALEthe storage OR DISTRIBUTION site for NOT FORthe SALE carbohydrates OR DISTRIBUTION defecation The physical process the excrement until into their constitu- polysaccharide A complex car- of excreting feces from the rectum. elimination, or def- ent sugars so that bohydrate composed of 11 or ecation, occurs. The they can be more linked simple sugars. Starches following sections will provide a more detailed explana- absorbed, trans- and glycogen are examples of tion of how and where each nutrient is digested and ported, and used by © Jones & Bartlett Learning, LLC polysaccharides.© Jones & Bartlett Learning, LLC absorbed.NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTIONthe cells of the body.

What happens to carbohydrates once they are put into the mouth? Colon © Jones & Bartlett Learning, LLC © JonesThe & digestive Bartlett process Learning, begins withLLC the mechanical actions NOT FOR SALE OR DISTRIBUTION Absorbs water, NOT FORof mastication SALE OR and DISTRIBUTION the activity of an enzyme found in the sodium, chloride, saliva secreted by the salivary glands. Saliva contains the potassium, and enzyme amylase, which begins the breakdown of starchy vitamin K. foods to individual glucose molecules. Bacteria digest amylase A digestive enzyme that © Jones & Bartlett Learning, LLC © Jones Starch& Bartlett is the Learning, only LLC small amounts of breaks down carbohydrates into NOT FOR SALE OR DISTRIBUTION NOT FORtype SALE of carbohydrate OR DISTRIBUTION fiber. simple sugars. Cecum and, besides fats, the only nutrient in starch The major plant storage which enzymatic Rectum form of carbohydrates. Starch is breakdown begins in composed of long chains of linked © JonesAnal canal & Bartlett Learning, LLC © Jones & Bartlett Learning,the mouth. LLC Although glucose molecules. NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTIONdigestion starts in Figure 2.6 the mouth, very little The large intestine. In the large intestine, bacteria break of the starch is completely broken down to glucose by the down dietary fiber and other undigested carbohydrates, time the food is swallowed and enters the esophagus. In releasing acids and gas. The large intestine absorbs water the short transit time through the esophagus to the stom- © Jones &and Bartlett minerals Learning,and forms feces LLC for excretion. © Jonesach, & amylase Bartlett continues Learning, its breakdown LLC of starch. NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

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Once in the stomach, the food is subjected to hydro- © Jones & Bartlett Learning, LLC © JonesThe & small Bartlett intestine Learning, is where the LLC majority of digestion chloric acid, which denatures the salivary amylase, thus and absorption of carbohydrates and other nutrients NOT FORhalting SALE enzymatic OR DISTRIBUTIONdigestion of starches in the stomach. NOToccurs. FOR In SALE the duodenum, OR DISTRIBUTION the bolus of food is exposed to However, the mechanical breakdown of food continues digestive enzymes from the pancreas, gallbladder, and through the churning and powerful contractions of the cells of the small intestine (see Figure 2.4). The pancreas smooth muscle in the stomach walls. The smooth mus- secretes pancreatic amylase. This enzyme continues the cle actions help to mix the© Jonesstomach & acid Bartlett into the Learning, food digestionLLC of starch, breaking it© down Jones into &the Bartlett disaccharide Learning, LLC bolus. This process, which prepares the food bolus for maltose. The muco- movement into the smallNOT intestine, FOR usually SALE takes OR 1DISTRIBUTION to 4 pancreatic amylase An enzymeNOT FORsal cells SALE and ORmicro DISTRIBUTION- hours. No absorption of carbohydrates or other nutrients, secreted by the pancreas into the villi of the intestinal except for alcohol, occurs in the stomach (see Figure 2.7 ); duodenum that assists in the diges- tract contain their these nutrients therefore pass on with the other gastric tion of starches. own enzymes called contents ©into Jones the small & Bartlett intestine. Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

Duodenum Alcohol

Carbohydrates, water, water-soluble vitamins Jejunum amino acids © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Fat, fat-soluble ph vessels NOT FOR SALE OR DISTRIBUTION vitamins,NOT cholesterol FOR SALE OR DISTRIBUTION

Portal vein Ileum

Left subclavian Water, vitamin K and left internal © Jones & Bartlett Learning, LLC © Jonesjugular & veinsBartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Liver

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the brush border disaccharidases. These enzymes go to © Jones & Bartlett Learning, LLC © Jonesthrough & Bartlett permeable Learning, cell membranes LLC driven only by dif- work on the food as it enters the small intestine and break ferences in concentration gradient. Passive diffusion is a NOT FOR SALE OR DISTRIBUTION down disaccharidesNOT FORnon-energy-requiring SALE OR DISTRIBUTION mechanism of absorption, and mol- brush border disacchari- into monosaccha- ecules always move from high concentration to low con- dases Digestive enzymes pro- rides, which are then centration. The bigger the difference in concentration, the duced by cells of the intestinal wall ready for absorption. greater the movement of molecules across the membrane. that break disaccharides into simple © Jones & BartlettThere are Learning,a variety of LLCMolecules can enter cells© by Jones passively & Bartlettdiffusing throughLearning, LLC sugars. disaccharidases that the cell membrane or by passing through protein chan- NOT FOR SALEfunction OR toDISTRIBUTION digest nels in the cell membraneNOT (see FOR Figure SALE 2.8a). Because OR DISTRIBUTION cell maltase A digestive enzyme that specific carbohy- membranes are composed of fatty substances, fats and breaks down maltose into two glu- drates. For example, fat-soluble molecules, such as oxygen, carbon dioxide, cose molecules. maltase splits the and alcohol, can pass directly through membranes dur- © Jones & Bartlett Learning,disaccharide LLC malt- ing passive© Jonesdiffusion. & Conversely, Bartlett Learning,water passively LLC diffuses sucrase A digestive enzyme that ose into two single across membranes using the protein channels in the cell breaksNOT down FOR sucrose SALE into glucose OR DISTRIBUTIONglucose molecules. membranes.NOT Unlike FOR water,SALE the OR water-soluble DISTRIBUTION nutrients, and fructose molecules. Sucrase splits such as carbohydrates, amino acids, minerals, and some sucrose into glucose vitamins, are not absorbed via passive diffusion and must lactase A digestive enzyme that and fructose. Lactase rely on other forms of transport, such as facilitated diffu- breaks lactose into the simple sug- © Jones & Bartlett Learning, LLC splits lactose into© Jonession & or Bartlett active transport. Learning, LLC ars galactose and glucose. glucose and galac- NOT FOR SALE OR DISTRIBUTION NOT FOR FacilitatedSALE OR diffusion DISTRIBUTION, similar to passive diffusion, tose. After enzymatic does not require energy, and molecules move from areas digestion of the carbohydrates, the resulting simple sug- of high concentration to low concentration; however, mol- ars are absorbed through the intestinal wall in the jeju- ecules must be carried across the membrane by protein num and upper ileum (see Figure 2.7) and enter the carriers (see Figure bloodstream. © Jones & Bartlett Learning, LLCfacilitated diffusion A means© Jones of 2.8b).& Bartlett The monosac Learning,- LLC When individuals have an insufficient supply of the cellular absorption in which pro- NOT FOR SALE OR DISTRIBUTION NOT FORcharide SALE fructoseOR DISTRIBUTION is enzyme lactase in their intestinal tract, they are not able tein carrier molecules are required absorbed via facili- to break down the milk sugar lactose. As a result, lactose to move substances across mem- tated diffusion, but goes undigested and is passed on to the large intestine, branes driven only by differences in because its passage where it is exposed to bacteria. The bacteria ferment lac- concentration gradient. through membranes tose in© theJones colon, & producing Bartlett gas Learning, and bloating. LLC Consuming © Jones & Bartlett Learning,is dependent LLC solely dairy products that have added lactase or taking prod- NOT FOR SALE OR DISTRIBUTION on concentrationNOT FOR gradients, SALE its OR absorption DISTRIBUTION is slower than ucts like Lactaid before consumption of dairy foods can that of other monosaccharides, such as glucose and galac- decrease or eliminate these symptoms. tose, which are absorbed by active transport. Any unabsorbed and/or undigested polysaccharides, Active transport is an energy-requiring form of such as fiber, that make it through the small intestine absorption that requires transporter proteins, but, unlike enter into the large intestine, where some bacterial diges- © Jones & Bartlett Learning, LLC © Jonesfacilitated & Bartlett diffusion, Learning, the direction LLC of the transport is not tion and gas formation can occur. However, no absorption dictated by concentration gradients (see Figure 2.8c). In NOT FORof SALE carbohydrates OR DISTRIBUTION occurs in the large intestine, and thusNOT FORother SALE words, OR during DISTRIBUTION active transport, molecules can be any remaining carbohydrates pass through the system moved against con- and are eliminated as feces. Figure 2.7 provides a graphic active transport An energy- centration gradients summary of nutrient absorption, showing that the major- requiring means of cellular absorp- (i.e., from low to high ity of carbohydrates are absorbed in the jejunum. © Jones & Bartlett Learning, LLCtion in which substances are© carried Jones concentrations).& Bartlett Learning, The LLC across membranes by protein mole- monosaccharides How are the simpleNOT sugars FOR absorbed SALE OR into DISTRIBUTION the cules. Active transport is not NOTdepen- FORglucose SALE andOR galacDISTRIBUTION- intestinal wall? dent on concentration gradients. tose are absorbed There are four ways that nutrients can be absorbed into across the intestinal the intestines: passive diffusion, facilitated diffusion, lining via active transport. The name of the transporter active© transport,Jones & andBartlett endocytosis Learning, (see FigureLLC 2.8 ). The protein ©found Jones in the & intestines Bartlett is Learning, SGLUT1. For LLC SGLUT1 to following is a brief transport these simple sugars through the intestinal cell NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION passive diffusion A means of overview of how membrane, it must first bind to a sodium ion. Conversely, cellular absorption in which the these absorptive pro- if no sugars are available, the bound sodium is not trans- movement of molecules through cesses are used for ported into the cell either. In other words, SGLUT1 must permeable cell membranes is carbohydrates. bind both a sodium ion and sugar for transport into the © Jones & drivenBartlett only byLearning, differences in LLC con- Passive diffusion© Jonescell & to Bartlett occur. This Learning, is the reason LLC why physiology books centration gradient. involves the move- refer to this specific active transport process as a glucose– NOT FOR SALE OR DISTRIBUTION ment of moleculesNOT FORsodium SALE symport. OR DISTRIBUTION

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FACILITATED DIFFUSION

PASSIVE DIFFUSION High High © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Water and water soluble substances (e.g., urea,NOT glycerol) FOR and small SALE lipids OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION move with a concentration gradient.

Cell membrane © Jones & BartlettTube-shaped Learning, LLC © Jones & BartlettTransmembrane Learning, protein LLC carrier transmembrane changes shape to facilitate entry NOT FOR SALEprotein OR channel DISTRIBUTION NOT FOR SALE ORand DISTRIBUTION exit of some nutrients Low (e.g., fructose). Low

© Jones & Bartlett Learning, LLC ENDOCYTOSIS© Jones & Bartlett Learning, LLC ACTIVENOT TRANSPORT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Low Minerals, some sugars, and most amino acids move against a concentration gradient with an input of energy. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION The cell membrane surrounds small molecules and engulfs them. Concentration © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

ATP

Figure 2.8 Mechanisms for nutrient absorption. (a) Passive diffusion. Using passive diffusion, some substances easily move in and out© of Jones cells, either & Bartlett through proteinLearning, channels LLC or directly through the cell© membrane.Jones & (b)Bartlett Facilitated Learning, diffusion. LLC Some substancesNOT FOR need SALE a little OR assistance DISTRIBUTION to enter and exit cells. The transmembraneNOT FOR protein SALE helps OR out DISTRIBUTION by changing shape. (c) Active transport. Some substances need a lot of assistance to enter cells. Similar to swimming upstream, energy is needed for the substance to penetrate against an unfavorable concentration gradient. (d) Endocytosis. Cells can use their cell membranes to engulf a particle and bring it inside the cell. The engulfing portion of the membrane separates from the cell wall and encases the particle in a vesicle. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

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Endocytosis is a means of cellular uptake that What happens to carbohydrates once they © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC involves the cell membrane encircling molecules and make it to the cells of the body? NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION internalizing them Once glucose is transported to various bodily tissues, such endocytosis A means of cellular (see Figure 2.8d). as skeletal muscle, it must gain access to the inside of tis- absorption in which substances are Although the process sue cells in order to be used for energy or to be stored. encircled by the cell membrane and of endocytosis does Unlike intestinal absorption, in which glucose is actively internalized into the cell. © Jones & Bartlettoccur in cellsLearning, lining LLCtransported via SGLUT1, glucose© Jones in the & bloodBartlett is taken Learning, into LLC the GI tract, it is not a NOT FOR SALE OR DISTRIBUTIONthe cells by specialized transporterNOT FOR proteins SALE via OR facilitated DISTRIBUTION process that accounts for carbohydrate uptake. diffusion. These specialized membrane proteins are called Of the four mechanisms, facilitated diffusion and glucose transporters (GLUT) and are present in all cells active transport explain carbohydrate absorption by the in the body. Some of these glucose transporters are stimu- cells lining the small intestine. lated by the hormone insulin, which, in turn, increases the rate of cellular What© happens Jones & to Bartlett carbohydrates Learning, once LLC they © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION glucoseNOT transporters FOR (GLUT) SALESpe OR- DISTRIBUTIONglucose uptake. make it into the blood? cialized membrane carrier proteins Several differ- Once the simple sugar molecules cross the intestinal cell that are responsible for the active ent types of glu- membranes and enter the blood, they are transported to transport of glucose into cells. cose transporters the liver via the hepatic portal system. This system is a net- are present in vari- © Jones &work Bartlett of blood Learning, vessels that LLCcollects the absorbed nutrients© Jones ous & tissues Bartlett throughout Learning, the LLCbody. In regard to muscle, from the small and large intestines and delivers them to the NOT FOR SALE OR DISTRIBUTION NOT FORthe transporters SALE OR areDISTRIBUTION called GLUT1 and GLUT4. At rest or liver (see Figure 2.7). No special carrier proteins are required when blood levels of the hormone insulin are low, most when the sugars reach the bloodstream because they are glucose enters muscle cells via the GLUT1 transporter. soluble in water (i.e., blood plasma). Once the bloodborne However, when glucose and insulin levels in the blood simple sugars reach the cells of the liver, those that are not are high (e.g., after a meal) or when muscle is active (e.g., in the form of glucose© (e.g., Jones fructose, & Bartlett galactose) Learning, are con- LLCduring exercise), the GLUT4© Jones transporter & Bartlett protein is Learning, stimu- LLC verted to glucose. NOT FOR SALE OR DISTRIBUTIONlated and becomes the majorNOT transporter FOR SALE of glucose OR DISTRIBUTION into glycogen The storage form of car- The glucose can then the muscle cells. Once the glucose has gained entrance bohydrates in animal cells. Glyco- be stored as glyco- into a cell, it has several fates, depending on the type of gen consists of intricately branched gen in the liver cells cell it enters. In a liver cell, for example, glucose can be chains of linked glucose molecules. or released into the stored as glycogen, converted to a fatty acid and released © Jones & Bartlett Learning,bloodstream. LLC into the© bloodstream, Jones & Bartlettor it can remainLearning, a glucose LLC mole- Rising blood glucose levels after ingestion of carbo- NOT FOR SALE OR DISTRIBUTION cule andNOT flow fromFOR the SALE liver to OR other DISTRIBUTION cells throughout the hydrates stimulates the release of insulin, which is a hor- body via the bloodstream. When a glucose molecule in mone secreted by the blood reaches muscle cells, adipose tissues, or other insulin A hormone secreted by specialized cells types of cells, it can be taken up from the blood and either specialized cells within the pancreas within the pancreas stored, used for energy, or converted to fat (see Figure 2.9 ). that lowers blood glucose levels known as beta cells. © Jones & Bartlett Learning, LLC © JonesIf it & is Bartlettstored, the Learning, glucose molecule LLC can be linked to other after snacking or meals. The release of insu- glucose molecules, forming the complex carbohydrate NOT FOR SALE OR DISTRIBUTION lin into the bloodNOT- FORknown SALE as glycogen. OR DISTRIBUTION Glucose can remain stored as glyco- beta cells Specialized cells within stream causes gen in the cell until it is needed for energy, at which point the pancreas that secrete the hor- glucose transporter it is cleaved from the glycogen chain and metabolized. mone insulin. proteins (see next © Jones & Bartlettsection) withinLearning, the LLC © Jones & Bartlett Learning, LLC diabetes A medical disease that cell membranes of How are fats digested, absorbed, is characterized by highNOT blood FOR SALEmuscles OR and DISTRIBUTION other NOT FOR SALE OR DISTRIBUTION glucose levels. Diabetes results tissues to begin the transported, and assimilated in the body? when either the beta cells of the uptake of glucose, Although fats are made up of carbon, hydrogen, and oxy- pancreas do not produce enough thereby preventing gen atoms similar to carbohydrates, they have very dif- insulin or the body's tissues do not © Jones & Bartlett Learning,blood LLCglucose levels ferent chemical© Jones structures & Bartlett and physicalLearning, properties. LLC Fats respond normally to insulin when it from rising too high. are molecules that belong to a group of compounds is produced.NOT FOR SALE OR DISTRIBUTIONDiabetes results NOT FOR SALE OR DISTRIBUTIONknown as lipids, when the beta cells lipids A class of organic compounds which are organic do not produce enough insulin to lower blood glucose lev- that is insoluble in water and greasy compounds that are els, or the beta cells produce insulin to which the body’s to the touch. Lipids are commonly insoluble in water © Jones &tissues Bartlett do not Learning, respond normally. LLC The end result is abnor©- Jonesreferred & Bartlett to as fats Learning, and exist in the LLC and feel greasy to the mally high blood glucose levels, sometimes in excess of body primarily as triglycerides. touch. Sources of NOT FORtwo SALE to four OR times DISTRIBUTION the normal level. NOT FOR SALE OR DISTRIBUTIONdietary lipids are

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NOT FOR SALEGlucose OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

Tr iglycerides

Liver © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

Glucose Glucose © Jones & BartlettGlucose Learning, LLC © Jones & Bartlett Learning, LLC Glycogen NOT FOR SALE OR DISTRIBUTIONα-GlycerolphosphateFatNOTty acids FOR SALE OR DISTRIBUTION

CO2 + H2O + Energy Muscle

Tr iglycerides © Jones & Bartlett Learning,Almost all tissuesLLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FORAdipose SALE tissues OR DISTRIBUTION Figure 2.9 Flowchart of glucose and other simple sugars immediately after a meal.

© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION butter, margarines, salad dressings, and oils. Lipids are may be removed, also found in meats, dairy products, nuts, seeds, olives, monoglyceride A lipid composed leaving a diglyceride, avocados, and some grain products. Most dietary lipids of a glycerol molecule with one or two fatty acids may exist in the form of triglycerides; therefore, the following attached fatty acid. be removed, leaving a discussion will focus on the© Jonesdigestion, & absorption, Bartlett Learning, trans- LLC © Jonesmonoglyceride & Bartlett. TheLearning, LLC NOT FORport, SALE and ORassimila DISTRIBUTION- free fatty acid Compounds comNOT- FORfatty SALEacids cleaved OR DISTRIBUTION triglyceride A lipid that is com- tion of triglycerides posed of long hydrogen-carbon off the glycerol back- posed of a glycerol molecule with (see Figure 2.10 ). chains that have a carboxyl group bone become what three attached fatty acids. Fatty acids are on one end and a methyl group at are known as free basically carbon the other. Free fatty acids can be fatty acids. atoms that© areJones linked & in Bartletta chainlike Learning, fashion (see FigureLLC 2.11 ). formed when© a Jonesfatty acid is& cleaved Bartlett Learning,Fat digestion, LLC These chainsNOT of FOR carbon SALE can be ofOR varying DISTRIBUTION lengths, and thus from a triglycerideNOT molecule. FOR SALE ORabsorption, DISTRIBUTION and fatty acids can be classified as short (4 or fewer carbons), transport are more medium (6 to 10 car- elaborate than that of other macronutrients because of fat’s diglyceride A lipid that is com- bons), or long (12 or insolubility in water. For example, the majority of enzymes posed of a glycerol molecule with more carbons). Dur- involved in digestion are water soluble, which under normal © Jonestwo & attached Bartlett fatty Learning,acids. LLC ing triglyceride diges- © Jonescircumstances & Bartlett would Learning, prohibit them LLC from effectively acting NOT FOR SALE OR DISTRIBUTIONtion, one fatty acid NOTon FOR fats. However, SALE ORthe body’s DISTRIBUTION digestive system subjects fats

9781284103465_CH02_PASS05.indd 32 08/11/16 5:50 PM Chapter 2 Nutrients: Ingestion to Energy Metabolism 33

1 Tr iglyceride and 3 © Jones & Bartlett Learning, LLC 3 Fatty acids © Jones & Bartlett Learning, LLC molecules of water NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION H 1 H O H O H C H C H H C OH + OH C H C O C H H O H 2 O H © Jones & Bartlett Learning,C H LLC C© H Jones & Bartlett Learning, LLC H C OH + OH C H C O C NOT FOR SALE OR DISTRIBUTIONH NOTH FOR SALE OR DISTRIBUTION O H 3 O H C H C H H C OH + OH C H C O C H H H H © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALEGlycerol OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

H2OH2OH2O

Figure 2.10 © Jones &Forming Bartlett a triglyceride. Learning, Concentration LLC reactions attach three© Jones fatty acids & Bartlett to a glycerol Learning, backbone LLC to form a triglyceride. NOT FORThese SALE reactions OR DISTRIBUTION release water. NOT FOR SALE OR DISTRIBUTION

H O H C C © Jones & Bartlett Learning,C LLCC OH © Jones & Bartlett Learning, LLC H NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

H O H C C C C C C C C C C OH More solid © Jones & Bartlett Learning, LLCMore liquid H © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

O H C C C C C C C C C C C C C C C C OH H © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

Figure 2.11 Fatty© acids Jones vary in& lengthBartlett and Learning,can be classified LLC as short, medium, or long.© The Jones longer & the Bartlett fatty acid, Learning, the more solid LLC it is at room temperature. NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION to substances known their job. Emulsifiers are substances that break lipids into emulsifier A substance that breaks as emulsifiers, which very small globules that stay suspended in the watery con- lipids into very small globules so work around the tents of the GI tract and increase the exposed surface area that they are more manageable in insolubility issue and of fats to the actions of digestive enzymes. Without being © Jones & wateryBartlett fluids. Learning, LLC allow enzymes to ©do Jonesemulsified, & Bartlett the fats Learning, would tend LLC to stick together in large NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

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clumps, making it difficult for enzymes to do their jobs. such as pancreatic © JonesAs noted & Bartlett earlier, theLearning, following LLCdiscussion focuses on the © Jonespancreatic & Bartlett lipase Learning,A digestive LLClipase and other NOT FORdigestion SALE of triglycerides. OR DISTRIBUTION NOT enzymeFOR SALEsecreted ORby the DISTRIBUTION pancreas digestive enzymes, into the duodenum that breaks allowing the enzy- What happens to fats once they are put into the down triglycerides. matic breakdown of mouth? foods to progress. Mastication breaks up fat into smaller pieces, and lingual micelles Tiny bubbles made up © Jones & Bartlett Learning, LLC © JonesThe & Bartlettpancreatic Learning, LLC lipase in saliva initiates the enzymatic digestive process. of monoglycerides and long-chain lipase is released in NOT FORHowever, SALE ORbecause DISTRIBUTION fatty acids that are wrapped NOTin FORlarge SALEamounts OR and DISTRIBUTION lingual lipase An enzyme for fat food is in the mouth bile salts. Micelles help transport finishes the diges- digestion that is secreted by cells for a relatively short digested fats to the intestinal wall tive process of fats, located at the base of the tongue. period of time before for absorption. thereby breaking the being swallowed, © Jones & Bartlett Learning, LLC © Jones & Bartlettremaining Learning, triglycer LLC - very little fat is actually digested in the mouth. ides into glycerol, monoglycerides, and free fatty acids WhenNOT food FORis swallowed, SALE theOR lingual DISTRIBUTION lipase is passed of various lengths.NOT FORShort- SALE and medium-chain OR DISTRIBUTION fatty acids, into the stomach, where it continues to break down the which are water soluble, are absorbed into the intestinal fats, at least until it is denatured by stomach acid. Gastric lining via passive diffusion. The monoglycerides and lipase is secreted by the chief cells in the stomach lining long-chain fatty acids, which are water insoluble, are and continues the enzymatic digestive process in the © Jones & Bartlett Learning, LLC © Jonesencircled & Bartlettby bile salts, Learning, forming LLC microscopic bubbles stomach. The gastric known as micelles. The micelles transport the long- NOT FORgastric SALE lipase ORA DISTRIBUTIONfat-digesting lipase breaks the tri- NOTchain FOR fatty SALE acids OR and DISTRIBUTIONmonoglycerides to the cells lining enzyme secreted by cells of the glycerides into the intestinal walls, at which time they are released stomach. diglycerides, which from the micelles and passively diffused into the interior aid in the digestive of the intestinal cells. Figure 2.12 provides a graphic sum- process by serving as emulsifiers. Churning and muscular © Jones & Bartlett Learning, maryLLC of triglyceride digestion.© Jones & Bartlett Learning, LLC contractions of the muscles in the stomach wall also Fat digestion and absorption are for the most part assist in breaking apart largeNOT pieces FOR of SALE food and, OR in DISTRIBUTIONcom- completed by the time the foodNOT contents FOR reachSALE the OR large DISTRIBUTION bination with emulsifiers, help keep the fats dispersed intestine. Minimal amounts of fat are found in the large and in suspension. After 2 to 4 hours in the stomach, intestine or passed in fecal matter. However, some dis- approximately one-third of the dietary triglycerides have ease conditions can been broken down into diglycerides and free fatty acids.1 steatorrhea An abnormal condi- cause fat malabsorp- As the© foodJones contents & Bartlett reach theLearning, small intestine, LLC the © Jones & Bartlett Learning, LLC tion in which large amounts of fat tion, resulting in ste- duodenal cells release hormones that stimulate the NOT FOR SALE OR DISTRIBUTION are found in NOTthe feces. FOR SALE ORatorrhea DISTRIBUTION, or fatty release of enzymes that further assist in lipid digestion. stools. Radiation For example, cholecystokinin (CCK) is released and trav- therapy for cancer, digestive surgeries requiring a large els via the blood to the pancreas and gallbladder. CCK portion of the small intestine to be removed, Crohn’s dis- stimulates the pancreas to produce large quantities of ease, and cystic fibrosis all can cause fat malabsorption. © Jonesdigestive & Bartlett enzymes Learning, that are delivered LLC to the duodenum © Jones & Bartlett Learning, LLC NOT FORvia the SALE bile duct. OR CCK DISTRIBUTION also stimulates the gallbladder to NOTWhat FOR happens SALE OR to the DISTRIBUTION fats once they are contract, forcing bile absorbed? and pancreatic cholecystokinin (CCK) A hor- Once absorbed, the water-soluble glycerol and short- and enzymes down the mone produced by cells of the medium-chain fatty acids pass through the intestinal cells bile duct and into small intestine that stimulates the and diffuse into capillaries, thus entering directly into the © Jonesthe & Bartlettduodenum Learning, (see LLC © Jones & Bartlett Learning, LLC release of bile salts and pancreatic bloodstream (see Figure 2.13 ). The monoglycerides and Figure 2.2). Bile is enzymes. NOT FOR SALE OR DISTRIBUTIONlong-chain fatty acids that areNOT absorbed FOR are SALE reassembled OR DISTRIBUTION important in the fat into triglycerides within the intestinal cells. The resynthe- digestion process secretin A hormone released from sized triglycerides because it contains lipoproteins Substances that the duodenum that stimulates the are then combined bile salts and leci- transport lipids in the lymph and release of bicarbonate from the with protein carriers © Jones & Bartlett Learning,thin (a type LLC of lipid), blood. These© substances Jones consist& Bartlett of Learning, LLC pancreas. to form lipoproteins. NOT FOR SALE OR DISTRIBUTIONwhich keep the fats a central coreNOT of triglycerides FOR SALE sur- ORThese DISTRIBUTION lipoproteins emulsified so that rounded by a shell composed of with their fatty cargo the water-soluble digestive enzymes can continue to do proteins, phospholipids, and choles- then pass through their job. Secretin, released from duodenal cells, stimu- terol. Various types of lipoproteins the intestinal cells. lates the pancreas to release bicarbonate, which neutral- exist in the body and differ based Once they leave the © Jonesizes &the Bartlett acidity ofLearning, the intestinal LLC contents. Neutralizing © Joneson size, & composition, Bartlett andLearning, density. LLCintestinal cells, they NOT FORthe acids SALE prevents OR DISTRIBUTION denaturation of protein enzymes, NOT FOR SALE OR DISTRIBUTION

9781284103465_CH02_PASS05.indd 34 08/11/16 5:50 PM Chapter 2 Nutrients: Ingestion to Energy Metabolism 35

Mouth Salivary glands Lingual Fats become © Jones & Bartlett Learning, LLC lipase © Jonestiny & droplets. Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

30% of triglycerides Stomach Stomach Gastric become diglycerides © Jones & Bartlett Learning, LLC lipase© Jones & Bartlett Learning,and fatty acids. LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

Small Pancreatic Tr iglycerides and Pancreas intestine lipase diglycerides become © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLCglycerol, monoglycerides, NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTIONand free fatty acids.

Figure 2.12 Triglyceride digestion. Most triglyceride digestion takes place in the small intestine. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC

NOT FOR SALEare called OR DISTRIBUTIONchylomi- new glycerol from insideNOT the FORcells andSALE once OR again DISTRIBUTION re- chylomicron A droplet made of crons. Chylomicrons formed into triglycerides. These newly formed triglycerides resynthesized triglycerides wrapped do not enter directly are stored until needed for energy. However, if the muscles in lipoproteins that is produced by into the bloodstream, are active and need energy, free fatty acids and chylomi- the intestinal cells. Chylomicrons © Jones & Bartlett Learning,but instead LLC enter crons in© blood Jones flowing & Bartlettthrough the Learning, capillaries LLCof muscles are passed from the intestinal cells into the lymphatic can be used for energy. LPL in the capillaries of muscles whereNOT they FORthen enter SALE into the OR lym -DISTRIBUTIONsystem (see Figure acts uponNOT the triglyceridesFOR SALE in ORthe chylomicrons, DISTRIBUTION similar to phatic system. 2.13). The lymphatic the LPL in adipose tissues. The free fatty acids in the blood, system then delivers in addition to those released from the chylomicrons, are the chylomicrons to the large veins of the neck via the transported across the muscle cell membrane and into the thoracic duct. The fats then empty into the blood and are interior of the cell where they are used for energy. © Jones &distributed Bartlett throughout Learning, the LLC body. © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION How are proteins digested, absorbed, What happens to fats once they make it to the cells? transported, and assimilated in the body? Fats have many functions within the body. However, bio- Of the three macronutrients, proteins are the least used energetically, depending© Joneson the physical & Bartlett state ofLearning, the body, LLCby the body as a source of© chemical Jones energy; & Bartlett however, Learning, they LLC the type of cell, and the need for energy, once fats reach play the biggest role in providing structure to the body. the cells they can be eitherNOT FORused for SALE energy OR or storedDISTRIBUTION for Proteins also form the enzymesNOT FOR critical SALE to the ORthousands DISTRIBUTION later use. For example, if energy demands are low and the of chemical reactions required to sustain life. bloodborne chylomicrons and their fatty payloads enter Proteins are made up of basic building blocks called capillaries within adipose tissue or the liver, the chylomi- amino acids. The proteins important to the human body crons© can Jones be acted & uponBartlett by an Learning, enzyme located LLC on the cap- are composed© Jones of 20 & different Bartlett amino Learning, acids. To LLC make the illary wall called lipoprotein lipase (LPL). LPL breaks the proteins required, dietary proteins must supply the nec- triglyceridesNOT FOR inside SALE the chylomicrons OR DISTRIBUTION into free fatty acids essary aminoNOT acids.FOR TheSALE following OR DISTRIBUTION sections discuss how and glycerol. The free dietary proteins are digested and utilized by the body. lipoprotein lipase (LPL) A spe- fatty acids immedi- cialized enzyme that breaks down ately diffuse into the What happens to proteins once they are put © Jones & triglyceridesBartlett intoLearning, glycerol and LLC free fat or liver cells,© Jones into & theBartlett mouth? Learning, LLC fatty acids. where they are Once again, mastication initiates the digestive pro- NOT FOR SALE OR DISTRIBUTION recombined withNOT a FORcess; SALE however, OR unlike DISTRIBUTION carbohydrates and fats, which are

9781284103465_CH02_PASS05.indd 35 08/11/16 5:50 PM 36 Section 1 The Basics of Sports Nutrition

Long-chain © Jones & Bartlett Learning, LLC fatty acids © Jones & Bartlett Learning, LLC Phospholipids NOT FOR SALE OR DISTRIBUTIONCholesterol NOT FOR SALE OR DISTRIBUTION Monoglycerides

Enzymes Bile salts © Jones & Bartlett Learning,Fat LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR dropletDISTRIBUTION NOT FOR SALE OR DISTRIBUTION Glycerol, short- and medium-chain fatty acids are absorbed Enzymes and bile from small intestine Emulsification salts emulsify the into blood © Jones &fat Bartlettdroplets to fo Learning,rm LLC © Jones & Bartlett Learning, LLC micelles NOT FOR SALE OR DISTRIBUTION NOTGlycerol FOR SALEShort-chain OR DISTRIBUTION fatty acids

Micelles Medium-chain © Jones & Bartlett Learning, LLC © Jones & Bartlettfatty acids Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

Bile salts are recycled Micelles deliver their fatty © Jonescargo & Bartlettto the intestinal Learning, cells LLC © Jones & Bartlett Learning, LLC

NOT FOR SALE OR DISTRIBUTION NOT FORDiffusion SALE OR DISTRIBUTION

Cholesterol Long-chain fatty acid © Jones & Bartlett Learning, LLC +© Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION Phospholipids NOTMonoglycerides FOR SALE OR DISTRIBUTION

Chylo- Lipo- Reformed micron protein triglycerides

© Jones & Bartlett Learning, LLC Intestinal cells package ©cholesterol, Jones & Bartlett Learning, LLCDiffusion NOT FOR SALE OR DISTRIBUTION triglycerides, and phospholipidsNOT FOR into SALE OR DISTRIBUTION lipoproteins that are secreted into the lymph

Lymphatic vessel Blood capillary © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

Figure 2.13 Summary of lipid absorption. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC subjected to digestive enzymes present in the saliva, pro- the amino acids more teins do NOTnot undergo FOR SALEenzymatic OR digestion DISTRIBUTION in the mouth. denaturation NOTA process FOR by SALE which ORaccessible DISTRIBUTION to diges- The majority of protein digestion occurs in the stomach proteins lose their three-dimen- tive enzymes. The and upper portion of the small intestine. Hydrochloric sional shape and as a consequence acidic environ- acid (HCl) secreted by the stomach lining denatures pro- their enzymatic activity. ment, along with the © Jonesteins. & DenaturationBartlett Learning, is the process LLC by which the three- © Jones & Bartlett Learning, LLCchurning of the food dimensional shape of the protein begins to unravel contents via the muscular contraction of the stomach, NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION (see Figure 2.14 ). This makes the chemical bonds between allows for greater mixing with the HCl, thereby allowing

9781284103465_CH02_PASS05.indd 36 08/11/16 5:51 PM Chapter 2 Nutrients: Ingestion to Energy Metabolism 37

The final stage of protein digestion occurs inside © Jones & Bartlett Learning, LLC © Jonesthe & intestinal Bartlett cells Learning, after absorption. LLC Once inside the NOT FOR SALE OR DISTRIBUTION NOT FORintestinal SALE cells, OR other DISTRIBUTION peptidases break the remaining chemical bonds in the protein chains to produce individual amino acids. Some of the absorbed amino acids are used by the intestinal cells themselves. © Jones & Bartlett Learning, LLCThe majority of amino ©acids Jones are transported & Bartlett out Learning, LLC of the intestinal cells via facilitated diffusion and NOT FOR SALE OR DISTRIBUTIONenter into the portal systemNOT of FOR blood SALE vessels OR that DISTRIBUTION Heat (or other conditions) go directly to the liver. Amino acids are then either used by the liver or released into the general cir- culation Figure 2.15 provides a graphic summary of © Jones & Bartlett Learning, LLC protein digestion.© Jones & Bartlett Learning, LLC Digestion and absorption of protein are quite NOT FOR SALE OR DISTRIBUTION efficientNOT in the FOR stomach SALE and OR small DISTRIBUTION intestine, and, as a result, very little protein makes it to the large intestine. Protein that does end up in the large intestine is excreted in the feces. Some medical condi- © Jones & Bartlett Learning, LLC © Jonestions & mayBartlett cause Learning, protein digestion LLC and absorption problems, and it is important for the sports nutrition NOT FOR SALE OR DISTRIBUTION NOT FORprofessional SALE toOR be DISTRIBUTIONaware of these conditions in order Figure 2.14 to adapt the dietary plan, particularly when dealing Denaturation. Exposing a protein to heat, acids, oxida- with athletes. For example, celiac disease is a digestion, and mechanical agitation can destabilize it, causing tive disorder that involves the inability to digest cer- it to unfold and lose its© functional Jones & shape. Bartlett Learning, LLCtain plant proteins. Athletes© Jones with celiac & Bartlett disease are Learning, LLC not able to digest the protein in wheat, rye, oats, NOT FOR SALE OR DISTRIBUTIONand other grains. BecauseNOT these FOR grains SALE are excelOR -DISTRIBUTION lent sources of carbohydrates that athletes need for for a more thorough denaturation of the proteins. In addi- energy, the sports nutrition professional must work tion to the HCl, the enzyme pepsin begins breaking the closely with the athlete to find alternative plant proteins© Jones made up& Bartlettof longer chainsLearning, of amino LLC acids into protein/energy© Jones sources & Bartlett that will notLearning, exacerbate LLC the shorter amino acid chains. The enzyme pepsin in the symptoms and/or progression of the disease. stomachNOT is FORresponsible SALE for OR approximately DISTRIBUTION 10–20% of pro- NOT FOR SALE OR DISTRIBUTION tein digestion.2 However, at this stage in the digestive How are proteins absorbed into the intestinal process proteins are mostly broken down into smaller wall? protein chains rather than single amino acids. Amino acid absorption occurs through facilitated The majority of digestion of protein takes place in diffusion and active transport (see Figures 2.8b and © Jones &the Bartlett small intestine, Learning, where LLC additional protein-digestive© Jones2.8c). & TheBartlett majority Learning, of amino LLC acids require active NOT FORenzymes SALE calledOR DISTRIBUTION proteases break down the protein chainsNOT FORtransport SALE to ORgain DISTRIBUTION access into the intestinal cells. into even smaller units. Both the pancreas and small The active transport process for amino acids is the intestine make and release proteases. Cells lining the same as described for glucose earlier in the chap- small intestine also ter, although amino acids and glucose use different proteases A class of© protein-Jones & Bartlettsecrete peptidases Learning,, LLCtransport proteins. Similar© Jonesamino acids& Bartlett share the Learning, LLC digesting enzymes that break the which continue to same active transport systems and carrier proteins. chemical bonds holdingNOT amino FOR SALEbreak theOR short DISTRIBUTION pro- For example, the branchedNOT chain FOR amino SALE acids—leu OR -DISTRIBUTION acids together. tein chains into cine, isoleucine, and valine—all depend on the same lengths of three or carrier protein for absorption. Proteins consumed peptidases A group of protein- fewer amino acids. in the daily diet usually contain a variety of amino digesting enzymes that are released © Jones & Bartlett Learning,The resulting LLC sin- acids needed© Jones by the &body. Bartlett Because Learning, a variety of aminoLLC from cells of the small intestine. Pep- gle amino acids and acids are being moved into cells through a variety of tidasesNOT work FOR on breaking SALE the chemOR -DISTRIBUTIONprotein chains of differentNOT carrier FOR proteins, SALE competition OR DISTRIBUTION for the same ical bonds of short-chain proteins two or three amino membrane transporter is minimized, and the amino (i.e., three or fewer amino acids), acids are absorbed acids tend to be taken into the cell in proportions thereby yielding single amino acids. by either facilitated representative of the food’s composition. © Jones & Bartlett Learning, LLC diffusion or active© Jones &Taking Bartlett supplements Learning, containing LLC large amounts of transport. Most of the absorption takes place in the cells a single amino acid can affect the absorption of other NOT FORthat SALE line theOR duodenum DISTRIBUTION and jejunum. NOT FORamino SALE acids ifOR they DISTRIBUTION share the same transport carrier.

9781284103465_CH02_PASS05.indd 37 08/11/16 5:51 PM 38 Section 1 The Basics of Sports Nutrition

© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT1 FOR SALE OR DISTRIBUTION In the stomach, proteins are unfolded into long polypeptide chains of amino acids by the action of hydrochloric acid. The enzyme pepsin begins the digestion of polypeptides into shorter chains called peptides.

2 In the small intestine, proteases continue to break the © Jones & Bartlett Learning, LLC ©polypeptide Jones chains & intoBartlett smaller peptides. Learning, Different LLC enzymes called peptidases continue attacking the NOT FOR SALE OR DISTRIBUTION NOTpeptide bondsFOR to yieldSALE tripeptides OR and dipeptidesDISTRIBUTION as well as single amino acids.

Amino acid 3 These short peptides and amino acids can be absorbed by intestinal cells. © Jones & Bartlett Learning, LLCInside the cell, the peptides are completely© broken Jones down into & amino Bartlett acids Learning, LLC NOT FOR SALE OR DISTRIBUTIONby intestinal peptidases. The individual aminoNOT acids areFOR absorbed SALE into the OR DISTRIBUTION Capillary capillaries of the villi and transported to the liver via the portal vein. network

4 Amino acids are transported to the liver via the portal vein. The liver can use amino acids to manufacture a variety of important substances. © Jones & Bartlett Learning,Lymph LLC © JonesThose amino & Bartlettacids not used byLearning, the liver travel in theLLC NOT FOR SALE OR DISTRIBUTION NOTbloodstream FOR SALE to other tissues OR throughout DISTRIBUTION the body. Figure 2.15 The breakdown of protein in the body. Digestion breaks down protein into amino acids that can be absorbed.

© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC For example, athletes trying to increase muscle mass may primarily skeletal take supplements containingNOT highFOR doses SALE of ORa specific DISTRIBUTION amino acid pool The collectionNOT FORmuscle SALE and the OR liver DISTRIBUTION of amino acids found in body fluids amino acid or combination of amino acids. This may actu- (see Figure 2.16 ). The ally work against them because it could create competition and tissues that is available for pro- blood and its circu- for transport carriers that would result in the overabsorp- tein synthesis. lating amino acids tion of one amino acid at the expense of another. © Jones & Bartlett Learning, LLC © Jones & Bartlett makeLearning, up the LLCcentral part of the body’s amino acid pool. Amino acid concentra- NOT FOR SALE OR DISTRIBUTION tions in the bloodNOT are FOR in equilibrium SALE OR with DISTRIBUTION the amino acids What happens to amino acids once they make it in the other compartments making up the amino acid to the bloodstream? pool. However, relatively few amino acids are circulating The amino acids that enter the bloodstream after diges- in the blood compared to the quantity found in muscle tion of ingested proteins become part of the body’s amino © Jones & Bartlett Learning, LLC © Jonesand the & liver. Bartlett If amino Learning, acid levels fall LLC in one compartment, acid pool, which consists not only of bloodborne amino amino acids from the other compartments are mobilized NOT FORacids, SALE but also OR the DISTRIBUTION amino acids found in other tissues, NOTto FORcorrect SALE the imbalance. OR DISTRIBUTION This sharing of amino acids

9781284103465_CH02_PASS05.indd 38 08/11/16 5:51 PM Chapter 2 Nutrients: Ingestion to Energy Metabolism 39

Dietary Amino acids Pro when carbohydrate stores of energy are low and demands © Jones & Bartlett Learning, LLC te © Jones & Bartlett Learning, LLC protein from cell i n for energy are high. Alternatively, when amino acid levels

breakdown d

NOT FOR SALE OR DISTRIBUTION e NOT FOR SALE OR DISTRIBUTION

g are in excess they can be converted to fat and stored for

d later energy use by the body (see Figure 2.16).

t i

o The sharing of amino acids between compartments n is dynamic and ongoing. Proteins in the body are constantly turning over, requiring amino acids from the © Jones & BartlettBody Learning, proteins LLC © Jones & Bartlett Learning, LLC Amino acid pool on a continual basis. However, this sharing of NOTpool in cellsFOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Protein synthesis amino acids between compartments is a short-term fix for providing necessary amino acids. Daily dietary Synthesis of protein intake is essential to maintaining the body’s non-protein amino acid pool. If protein intake is not adequate, pro- molecules © Jones & BartlettLiver Learning, LLC teins from© Jonesmuscle &and Bartlett other tissues Learning, will be LLC cannibal- ized to provide the necessary amino acids, negatively NOT FORAmino SALECarbon OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION groups skeletons affecting an athlete’s training abilities and competitive performance.

Urea What happens to amino acids once they make it © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Fates of Carbon Skeletons to the cells of the body? NOT FOR SALE OR DISTRIBUTIONThe remaining carbon skeletons NOT FORThe aminoSALE acids OR circulatingDISTRIBUTION in the blood enter the cells can be used to make fatty acids or glucose, or broken down of the body by facilitated diffusion. Once inside the cells, completely to yield energy. the amino acids become the building blocks for specific

Kidney proteins. The specific protein constructed inside the cell is determined by current needs and/or the influences of © JonesUrea & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC The liver removes amino groups outside factors such as hormones. For example, the hor- NOT FORfrom SALEexcess amino OR acids DISTRIBUTION and mone testosterone causesNOT muscle FOR cells SALE to increase OR DISTRIBUTION pro- converts the amino groups to urea for excretion by the kidneys. duction of contractile proteins, thus causing the muscle to become bigger and stronger. Urea excretion The actual instructions for making the specific proteins © Jones & Bartlett Learning, LLC needed by© Jonesthe cell lie& inBartlett the strands Learning, of DNA (deoxyriboLLC - Figure 2.16 nucleic acid) found in the nucleus (see Figure 2.17 ). Seg- AminoNOT acid FORpool turnover. SALE ORCells DISTRIBUTIONdraw upon their amino NOT FOR SALE OR DISTRIBUTIONments of DNA that acid pools to synthesize new proteins. These small pools deoxyribonucleic acid (DNA) The call for specific pro- turn over quickly and must be replenished by amino acids molecular compound that makes teins are called genes. from dietary protein and degradation of body protein. up the genetic material found When a cell needs a Dietary protein supplies about one-third, and the break- within the nuclei of cells. particular protein, the © Jones &down Bartlett of body Learning, protein supplies LLC about two-thirds of the © Jones & Bartlett Learning, LLC specific gene with the NOT FORroughly SALE 300 OR grams DISTRIBUTION of body protein synthesized daily. NOT FORgene SALEA specific OR sequence DISTRIBUTION of DNA instructions for that When dietary protein is inadequate, increased degrada- found within cell nuclei that con- protein is copied in a tion of body protein replenishes the amino acid pool. This tains information on how to make process known as can lead to the breakdown of essential body tissue. enzymes or other proteins. transcription. Tran- © Jones & Bartlett Learning, LLC © Jones scription& Bartlett results Learning, in LLC transcription The process of copy- the formation of mes- between compartmentsNOT can FOR help SALE ensure OR that DISTRIBUTION needed ing genetic information fromNOT a spe- FORsenger SALE ribonucleic OR DISTRIBUTION amino acids are available when deficits arise. cific DNA sequence through the acid (mRNA), which is Amino acids in the pool can be used for a vari- formation of messenger RNA. a genetic set of ety of functions depending on the body’s needs. They instructions on how messenger ribonucleic acid are primarily used to make the protein. © Jones & Bartlett Learning, LLC (mRNA) © AJones type of &nucleic Bartlett acid Learning, LLC to synthesize new Upon leaving the cell Gaining the that carries the genetic instructions NOT FOR SALE OR DISTRIBUTIONstructural proteins, NOT FOR SALE OR DISTRIBUTIONnucleus, messenger Performance Edge for protein synthesis from the cell enzymes, hormones, RNA delivers the nucleus to the ribosomes located or other nitrogen- instructions to the Maintaining adequate protein in the cell cytoplasm. intake for athletes is essential for containing com- ribosomes, which are © Jones & theBartlett continual Learning,replenishment ofLLC the pounds. They can© Jonesribosomes & BartlettCellular Learning, organelles that LLC the cellular organ- amino acid pool. be metabolized for are responsible for protein synthesis. elles located in the NOT FOR SALE OR DISTRIBUTION energy, particularlyNOT FOR SALE OR DISTRIBUTIONcell cytoplasm that

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essential amino acids DNA © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLCGene 1 Gaining the are available when NOT FOR SALE OR DISTRIBUTION A speciﬁc NOT FOR SALEPerformance OR DISTRIBUTION Edge needed. One miss- length of DNA Nucleus ing essential amino serves as a An athlete's diet must include high- acid can stop the pattern to quality complete protein sources make mRNA construction of a mRNA or complementary protein foods protein. When this © Jones & Bartlett Learning, LLCso that the diet provides all of the© Jones & Bartlett Learning, LLC happens, the partially essential amino acids. Failure to do NOT FOR SALENuclear pore OR DISTRIBUTION NOT FORconstructed SALE proteinOR DISTRIBUTION 2 so will result in inadequate pro- is degraded, and its tein synthesis, ultimately affect- mRNA leaves amino acids are used the nucleus ing training, recovery, and sport elsewhere or metabo- and attaches performance. to a protein lized for energy. © ribosomeJones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Polypeptide How are minerals, vitamins, and water absorbed and transported in the body? © Jones & Bartlett Learning, LLC Ribosome © JonesMinerals, & Bartlettvitamins, Learning,and water (unlikeLLC carbohydrates, 3 proteins, and fats) do not need to be broken down into NOT FOR SALE OR DISTRIBUTIONtRNAs bring speciﬁc tRNA NOT FOR SALE OR DISTRIBUTION amino acids to the smaller units via digestion to be absorbed into the body. ribosome, where the As foodstuffs are being digested, the vitamins and miner- Cytoplasm amino acids are bound als within the foods are released into the intestinal con- to a protein chain tents. The majority of minerals released during digestion Figure 2.17 © Jones & Bartlett Learning, areLLC absorbed in the duodenum© andJones jejunum & Bartlett of the small Learning, LLC Protein synthesis. RibosomesNOT are FOR our protein-synthesis SALE OR DISTRIBUTION intestine. The exceptions areNOT sodium, FOR potassium, SALE OR and DISTRIBUTION factories. First mRNA carries manufacturing instructions chloride, which are absorbed in the large intestine. from DNA in the cell nucleus to the ribosomes. Then tRNA Vitamins are categorized as being either water solu- collects and delivers amino acids in the correct sequence. ble or fat soluble. The water-soluble vitamins (i.e., B-complex vitamins and vitamin C) dissolve in the watery mix © Jones & Bartlett Learning, LLC of food in the© GIJones tract and& Bartlett are absorbed Learning, along with LLC the build the protein. In a process known as translation, the NOT FOR SALE OR DISTRIBUTION water. The majorityNOT FOR of water SALE and ORall of DISTRIBUTION the water-soluble ribosomes read the mRNA segment and begin attaching vitamins (see Figure 2.7) are absorbed in the small intes- amino acids together tine. The water-soluble vitamins easily gain access to the translation The process in which in the sequence blood and move freely throughout the body within the proteins are produced by ribo- called for by the fluids both inside and outside of cells. instructions. The © Jonessomes & Bartlett as they read Learning, the genetic LLC © JonesThe & fat-soluble Bartlett vitamins Learning, (i.e., vitaminsLLC A, D, E, and K), instructions found on messenger amino acids needed when released from the digesting foods, dissolve in the fatty NOT FORRNA. SALE OR DISTRIBUTIONby the ribosomes are NOTportions FOR ofSALE the GI contents.OR DISTRIBUTION As a result, they are transported delivered to the “pro- along with the digested fats in micelles to the intestinal transfer ribonucleic acid tein construction wall where they are absorbed via passive diffusion. Similar (tRNA) A type of ribonucleic acid site” by transfer ribo- to the water-soluble vitamins, the majority of fat-soluble that is responsible for delivering © Jonesnucleic & Bartlett acid (tRNA)Learning,. vitamins LLC are absorbed in the small© Jones intestine & (seeBartlett Figure 2.7).Learning, LLC specific amino acids to the ribo- This process of tRNA A small amount of vitamin K is produced by bacteria in the some during production of protein.NOT FORdelivering SALE theOR needed DISTRIBUTION large intestine and is then alsoNOT absorbed. FOR OnceSALE inside OR the DISTRIBUTION amino acids to the intestinal cells, the fat-soluble vitamins are packaged into ribosomes continues until the protein has been the chylomicrons and then, along with other fats, trans- constructed. ported via the lymph into the bloodstream. From there they If an ©amino Jones acid &is requiredBartlett but Learning, not present atLLC the time are delivered© throughout Jones & the Bartlett body. Some Learning, are delivered LLC and of protein construction, the protein-building process is used by cells; others are stored along with fat in adipocytes. stopped. NOTIf the required FOR SALE amino acidOR isDISTRIBUTION a nonessential amino The fact thatNOT fat-sol FOR- SALE OR DISTRIBUTION acid, the cell makes the amino acid and tRNA delivers it, uble vitamins are Food for Thought 2.1 continuing the building process. However, if the amino acid stored in the body is needed is an essential amino acid, the building process can- one reason why tak- Digestion © Jonesnot continue,& Bartlett and Learning, the protein requestedLLC is not completed. © Jonesing high & dosagesBartlett of Learning, This exercise LLC tests your compre- This is why an athletic diet should include high-quality fat-soluble vitamins hension of the digestive process. NOT FORcomplete SALE or complementaryOR DISTRIBUTION proteins so that all of the NOTis notFOR recommended. SALE OR DISTRIBUTION

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BIODEGREDATION © Jones What& Bartlett is energy Learning, metabolism, LLC and why is it© Jones & Bartlett Learning, LLC important? Proteins Carbohydrates Fats NOT FOR SALE OR DISTRIBUTION NOT FOR SALE(amino OR acids) DISTRIBUTION(sugars) (fatty acids) Energy metabolism is a foundational component of sports nutrition. Knowledge of the cellular machinery and metabolic pathways responsible for deriving energy from the macronutrients once they reach the cells is critical to the sports nutrition© professional.Jones & Bartlett Without Learning,knowledge LLC © Jones & Bartlett Learning, LLC of the three energy systemsNOT FOR and how SALE they ORwork DISTRIBUTION together NOT FOR SALE OR DISTRIBUTION to supply energy during specific activities, the sports nutrition professional is severely disadvantaged in regard to creating an individualized dietary plan. Knowledge of Catabolic energy metabolism also enables the sports nutrition professional© Jones to objectively & Bartlett assess Learning, the potential LLC effective- © Jones & Bartlett Learning, LLC ness NOTof dietary FOR supplementation. SALE OR DISTRIBUTION Finally, comprehending NOT FOR SALE OR DISTRIBUTION energy metabolism enables sports nutrition profession- als to educate their athletes about the energy needs of their sport, thus helping to dispel many of the miscon- ceptions that abound in sports nutrition. The remainder © Jones &of thisBartlett chapter Learning, will define energy,LLC identify which nutrients© Jones & Bartlett Learning, LLC Energy NOT FORsupply SALE energy, OR DISTRIBUTIONand discuss how cells derive energy duringNOT FOR SALE OR DISTRIBUTION rest and exercise. Molecular building blocks (Amino Acids, Glucose, Fatty Acids) What is energy?© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Energy is an entity thatNOT is FORbetter SALEexplained OR or DISTRIBUTION defined NOT FOR SALE OR DISTRIBUTION than shown because it has no shape, no describable fea- Anabolic Energy tures, and no physical mass. Energy is what enables cells, muscles, and other tissues of the body to perform work, or, in© layperson’s Jones & terms,Bartlett to getLearning, things done. LLC The cellu- © Jones & Bartlett Learning, LLC lar and bodily functions that keep humans alive require energy.NOT Similar FOR to anSALE automobile OR DISTRIBUTION that relies on the chemi- NOT FOR SALE OR DISTRIBUTION cal energy of gasoline to run the motor, the cells of the body require chemical energy derived from the foods we eat to power their many different functions. In the © Jones &case Bartlett of sport Learning,performance, LLC the muscle cells must derive© Jones & Bartlett Learning, LLC enough energy from nutrients to fuel muscle contrac- NOT FORtion. SALE In short, OR an DISTRIBUTION understanding of energy, where it comesNOT FOR SALE OR DISTRIBUTION from, and how the body uses and stores metabolism The sum total of all Body protein Lipids the energy required to power cel- it is tantamount to understanding lular processes and activities.© Jones & Bartlett Learning, LLC Glycogen© Jones & Bartlett Learning, LLC metabolism. anabolic process A NOTmetabolic FOR SALEMetabolism OR DISTRIBUTION is NOT FOR SALE OR DISTRIBUTION function that involves the build- the sum total of the BIOSYNTHESIS ing of more complex structures or energy required by chemical molecules and is associ- the body to perform Figure 2.18 Metabolism. Catabolic processes result in biodegradation ated with the storage of energy. all of its functions © Jones & Bartlett Learning, LLC and energy© Jones release, &and Bartlett anabolic Learning,processes utilize LLC energy and thus is made up to drive biosynthesis. Metabolism consists of both cata- catabolicNOT FORprocess SALEA metabolic OR DISTRIBUTION of both anabolic and NOT FOR SALE OR DISTRIBUTION bolic and anabolic processes. function that involves the break- catabolic processes down of structures or molecules ( Figure 2.18 ). Anabolic and is associated with energy being processes involve example, when cells of the body use amino acids to make released. © Jones & Bartlett Learning, LLC the building of more© Joneshighly & Bartlett complex Learning,proteins or useLLC simple sugars to make complex structures glycogen for storage within the cells (see lower half of NOT FORor SALE chemical OR molecules DISTRIBUTION and require energy to occur; forNOT FORFigure SALE 2.18). ORConversely, DISTRIBUTION catabolic processes involve the

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© Jonesbreakdown & Bartlett of structures Learning, or molecules LLC and are associated © Jonesenergy for& Bartlett animal life Learning, originates from LLC plants. Specifically, with energy being released; for example, when proteins, the plants use radiant energy from the sun to build high- NOT FORcarbohydrates, SALE OR and DISTRIBUTION fats making up the foods we eat are NOTenergy FOR bonds SALE between OR DISTRIBUTION atoms of carbon, hydrogen, nitro- broken down and used to provide energy. The absolute gen, and oxygen. In doing so, plants form molecules of minimal amount of energy required to keep humans alive carbohydrates, proteins, and fats, which serve as energy is called basal metabolic rate (BMR). A slightly higher nutrients for the plants themselves, any animals that eat amount of energy is required© Jones for resting & Bartlett metabolic Learning, rate plants,LLC and on up the food chain.© Jones Because & animalsBartlett digest Learning, LLC (RMR). BMR and RMR are expressed in kilocalories (kcals), the consumed carbohydrates, fats, and proteins and can which are the commonly NOTused units FOR of SALE measurement OR DISTRIBUTION for convert them into their ownNOT forms FOR of each SALE (see ORFigure DISTRIBUTION energy. A kilocalo- 2.18), we can get basal metabolic rate (BMR) The rie is the amount of Gaining the energy nutrients, minimum amount of energy heat energy required Performance Edge also known as mac- required© to Jonessustain life & at Bartlettthe wak- Learning,to raise theLLC tem- © Jones & Bartlettronutrients, Learning, LLCfrom perature of 1 liter both plant and ani- ing state.NOT BMR is FOR usually SALEmeasured OR DISTRIBUTION MacronutrientsNOT are needed FOR inSALE large OR DISTRIBUTION in the laboratory under very rigor- of water 1 degree quantities compared to other nutri- mal sources. When ous conditions. centigrade, specifi- ents and act as sources of chemical plant and animal cally from 14.5°C energy in the body and as building foods are eaten, the resting metabolic rate (RMR) to 15.5°C. BMR and blocks for biosynthetic processes. digestive system © JonesThe & minimumBartlett amount Learning, of energy LLC RMR measurements © JonesThe macronutrients & Bartlett are Learning, more spe- LLCbreaks the nutrients NOT FORrequired SALE to ORmeet DISTRIBUTION the energy are obtained in dif- NOT cificallyFOR SALEknown as OR carbohydrates, DISTRIBUTION into their constitu- demands of the body while at rest. ferent ways. BMR fats, and proteins. ent parts so that RMR is typically measured instead is measured under they can be absorbed of BMR because it is only slightly very stringent con- and transported to higher than BMR and is determined ditions and requires the cells. The cells can then use the bloodborne nutrients under less rigorous conditions.© Jonessubjects & Bartlett to spend Learning, the asLLC building blocks for biosynthesis,© Jones store & themBartlett for later Learning, LLC NOT FORnight SALE in a ORsleep DISTRIBUTION lab. use, or metabolize them for NOTenergy FOR production. SALE OR DISTRIBUTION kilocalories (kcals) The unit of The subjects must measure for energy. It is the amount be well rested, ther- of heat energy required to raise the mally neutral (i.e., What is the human body’s source of temperature of 1 liter of water 1 neither hot nor cold), chemical energy? degree centigrade.© Jones & Bartlett Learning,and in a transitional LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTIONstate of waking (i.e., Based on theNOT previous FOR section, SALE it couldOR DISTRIBUTION be concluded that not asleep but not fully alert) at the time of the actual the chemical energy in carbohydrates, fats, and proteins is BMR measurement. RMR measures are much easier to the direct source of energy for cellular function. However, obtain. Subjects must fast for 12 hours but can drive to this is not the case. the laboratory, where they relax for 20 to 30 minutes in adenosine triphosphate (ATP) A The direct source of © Jonesa supine/reclined & Bartlett Learning, position before LLC their RMR is measured. © Joneschemical & Bartlettcompound thatLearning, contains LLCenergy for all bio- BMR and RMR are used by sports nutrition profession- three phosphate groups attached logical processes NOT FORals to SALEdetermine OR an DISTRIBUTION athlete’s 24-hour energy expenditure. NOT toFOR an adenosine SALE molecule.OR DISTRIBUTION ATP is comes from a high- This total daily energy expenditure can be used both to the direct source of energy for all energy molecule establish the dietary caloric intake necessary to achieve biological processes. known as adenosine energy balance and when counselling athletes in weight triphosphate (ATP). management. © Jones & Bartlett Learning, LLC © JonesIn short, & Bartlett the chemi Learning,- LLC Energy exists in six basic forms: chemical, nuclear, cal energy from mac- NOT FOR SALE OR DISTRIBUTION Gaining the NOT FOR SALE OR DISTRIBUTION electrical, mechanical, thermal, and radiant. However, Performance Edge ronutrients is used the form of energy that humans and animals directly to make another rely upon for survival is chemical energy. Chemical ATP is the body's direct source high-energy chemi- energy is energy that of chemical energy for powering cal known as ATP. The chemical© Jonesenergy Energy& Bartlett that Learning,is stored LLC within muscle contractions© Jones and & otherBartlett energy Learning, stored LLCin the is released as the bonds holding bonds between bodily functions. chemical bonds of chemicalsNOT together FOR are SALEbroken. InOR DISTRIBUTIONatoms of molecules. NOT FOR SALE ORATP DISTRIBUTION is released when the human body the foods ingested When the bonds the bonds are broken and can be used by the cells to per- provide chemical energy to make between these form biological work, as shown in Figure 2.19 . ATP, which is the ultimate source of atoms are broken, ATP is an adenosine molecule with a chain of three © Joneschemical & Bartlett energy in Learning, the body. LLC energy is released © Jonesphosphate & Bartlett groups attached Learning, to it in LLC series (see Figure 2.20 ). and can be used to The energy used by the body is stored in the molecular NOT FORperform SALE work. OR On earth,DISTRIBUTION the primary source of chemical NOTbonds FOR between SALE the OR second DISTRIBUTION and third phosphate groups,

9781284103465_CH02_PASS05.indd 42 08/11/16 5:51 PM Chapter 2 Nutrients: Ingestion to Energy Metabolism 43

Formation of ATP requires energy from as well as between the first and second groups. When © Jones & Bartlettthe Learning, metabolic breakdown LLC of energy nutrients © Jones & Bartlett Learning, LLC the bonds between the second and third or first and NOT FOR SALE OR DISTRIBUTION NOT FORsecond SALE phosphate OR DISTRIBUTION groups are broken, energy is released. Energy Some of the released energy is used to perform work, and the remainder is lost as heat energy, which cannot be used by the body. When the bond to the third phos- © Jones & Bartlett Learning, LLCphate group is broken, ©the Jones resultant & Bartlettproducts Learning,formed LLC are an adenosine diphosphate (ADP) and an unattached NOT FOR SALE OR DISTRIBUTION NOT FORinorganic SALE ORphosphate DISTRIBUTION adenosine diphosphate (ADP) A group (P ) (see Figure ADP + P i i ATP chemical compound that contains 2.20). ADP still has two phosphate groups attached to some energy poten- © Jones & Bartlett Learning, LLC an adenosine© Jones molecule. & ADP,Bartlett when Learning,tial for use LLC by the phosphorylated, becomes ATP. body. If the last NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTIONphosphate group is adenosine monophosphate cleaved from the (AMP) A chemical compound that ADP, the result is contains a single phosphate group the formation of Energy attached to an adenosine molecule. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC adenosine monophosphate (AMP) NOT FOR SALE ORBreakdown DISTRIBUTION of ATP releases energy to power: NOT FOR SALE OR DISTRIBUTION and another P (see Figure 2.20). Muscle activity i Nerve transmission Although ATP is the direct source of energy for cel- Biosynthesis lular functioning, it is stored in very small quantities in All other energy-requiring processes the cells. For example, in muscle cells, ATP stores are so © Jones & Bartlett Learning, LLCsmall they can be depleted© Jones in as little & Bartlett as 3 seconds Learning, of LLC Figure 2.19 NOT FOR SALE OR DISTRIBUTIONmuscle activity. Despite theNOT fact FOR that ATP SALE is stored OR inDISTRIBUTION very The ADP–ATP cycle. When extracting energy from nutri- limited amounts, it is important to note that cells never ents, the formation of ATP from ADP + P captures energy. i completely deplete their ATP stores. Figure 2.21 shows Breaking a phosphate bond in ATP to form ADP + Pi ATP levels during an intense sprint lasting 14 seconds. releases energy for biosynthesis and work. Note that at the point of exhaustion, roughly 30% of the © Jones & Bartlett Learning, LLC muscle’s© ATP Jones still remains.& Bartlett Obviously, Learning, athletes LLC perform NOT FOR SALE OR DISTRIBUTION activitiesNOT that FORlast longer SALE than OR 3 DISTRIBUTIONseconds every day, so ATP: Adenosine Triphosphate Inorganic the body must have ways of replenishing ATP once it is phosphate used. In fact, every cell, particularly muscle cells, can group Adenosine Pi Pi Pi replenish any ATP that is used to keep the ATP fuel tank somewhat full. If ATP levels fall too low because the © Jones & Bartlett Learning,2 LLChigh-energy bonds © Jones & Bartlett Learning, LLC Full NOT FOR SALE OR DISTRIBUTION ATP and ADP are NOT FOR SALE OR DISTRIBUTION interconvertible.

ADP: Adenosine Diphosphate

l ATP ve Adenosine © PJonesi P i& Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 1 high-energy bond

AMP: Adenosine Monophosphate Cell Le Muscle CP

AMP is inter- © JonesAdenosine & BartlettPi Learning,convertible LLC © Jones & Bartlett Learning, LLC with both Empty NOT FOR SALENo high-energy OR DISTRIBUTIONADP and ATP. NOT FOR SALE OR DISTRIBUTION phosphate bonds Start Exhaustion

12 sec. all out sprint Figure 2.20 ATP, ADP, AMP, and high-energy phosphate bonds. Your Figure 2.21 © Jones &body Bartlett can readily Learning, use the energy LLC in high-energy phos- © JonesEffect & Bartlettof intense Learning,activity on ATP LLC levels in muscle. Even phate bonds. During metabolic reactions, phosphate when an activity results in exhaustion, ATP levels are not NOT FORbonds SALE form OR or breakDISTRIBUTION to capture or release energy. NOT FORtotally SALE depleted. OR DISTRIBUTION

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activity is so intense that the muscle cells cannot make possesses a nucleus © Jones & Bartlett Learning, LLC © Jones & BartlettGaining the Learning, LLC ATP fast enough, protective mechanisms kick in that in that contains the Performance Edge NOT FORturn cause SALE fatigue OR .DISTRIBUTION Fatigue is a noted decrease in perfor- NOT FOR SALE OR DISTRIBUTIONgenetic information mance level, which slows down or even stops the activity Poor nutrition can directly affect ATP needed for making and thus protects production and thus decrease sport the enzymes and fatigue A physical condition the cell’s ATP levels. performance. cellular structures marked by the point in time at © JonesPoor & Bartlett nutrition Learning, can LLC © Jonesrequired & Bartlett for ATPLearning, LLC which the work output or perfor- directly affect ATP production. mance cannot be maintained.NOT FORproduction SALE OR and DISTRIBUTION thus To further explain ATP NOTformation, FOR aSALE basic ORunder DISTRIBUTION- decrease sport per- standing of bioenergetics is necessary. Bioenergetics is formance. As a result, there must be a way for cells to the study of how make or replenish ATP once it has been used. bioenergetics The study of energy energy is captured, © Jones & Bartlett Learning, LLC transfer within© a Jones biological &system. Bartletttransferred, Learning, and/orLLC utilized within bio- NOT FOR SALE OR DISTRIBUTION logical systems.NOT Because FOR thisSALE book OR deals DISTRIBUTION with sports, the How do cells make ATP? specific biologic system we will discuss in this chapter is To metabolize the energy nutrients, and in the process muscle. To rebuild ATP, unattached phosphates must be make ATP, the cells must possess the right metabolic reattached to AMP or ADP to re-form ATP. The process of © Jonesequipment. & Bartlett Although Learning, there are LLC many different types of © Jonesresynthesizing & Bartlett ATP requiresLearning, energy LLC in and of itself, and NOT FORcells thatSALE make OR up DISTRIBUTION the body, they all have similarities. NOTthis FOR is where SALE the OR energy DISTRIBUTION trapped in the bonds of foods Figure 2.22 provides the names and functions of many (i.e., macronutrients) comes into play. Using the analogy of the parts of typi- of a real-life factory, each of the muscle cells in the human cell membrane The membrane cal cells. For exam- body possesses what can be called a metabolic factory. that makes up the outer boundary ple, all cells have a These metabolic fac- of a cell and separates the internal© Jones cell & Bartlettmembrane Learning, that LLCmetabolic factory The cellular© Jonestories & are Bartlett responsible Learning, LLC contents of the cell from theNOT exter- FORencloses SALE ORthe DISTRIBUTIONcon- enzymes, organelles, and metabolicNOT FORfor manufacturing SALE OR DISTRIBUTION nal substances. tents of the cell, pathways responsible for the pro- the cells’ ultimate known as the cyto- duction of energy within the cells. energy source, ATP cytoplasm The interior of the cell. plasm. The Figure (see Figure 2.23 ). It includes the fluid and organelles 2.22 cell membrane Continuing with the metabolic factory analogy, inside that are© enclosed Jones within & Bartlett the cell Learning,serves as LLCa barrier the factory is© an Jones ATP pool & (i.e.,Bartlett the cell’s Learning, inventory ofLLC read- membrane. NOT FOR SALE OR DISTRIBUTIONthat regulates or NOT FOR SALE ORily DISTRIBUTION available energy). prevents the influx ATP pool The muscle cell’s inven- Whenever a cell of substances into or out of the cytoplasm. The watery tory of readily available ATP. needs quick energy, it component of the cytoplasm that fills much of the inte- does not need to wait rior of the cell is known as the cytosol. Dissolved in the for the metabolic factory to produce ATP because ATP is © Jonescytosol & Bartlett are enzymes, Learning, which are LLC proteins responsible for © Jonesalready &there Bartlett ready toLearning, be used. However, LLC the inventory of accelerating each ATP is very small and must be maintained above a certain NOT FORcytosol SALEThe watery OR DISTRIBUTIONor fluid part of step in the meta- NOTcritical FOR level, SALE because OR ifDISTRIBUTION the cell runs out of ATP, it can no the cytoplasm. bolic pathways longer function and dies. Fortunately, cells have three dif- responsible for gen- ferent energy systems (see Figure 2.23), each capable of organelles Specialized structures erating ATP. In addi- providing ATP and preventing depletion of the ATP pool. found inside cells that perform© Jones tion, & Bartlett within Learning, the The LLC following section discusses© Jones each energy & Bartlett system Learning, in LLC specific functions. For example, cytoplasm there are greater detail. the mitochondria are organellesNOT FORcellular SALE structures OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION responsible for the aerobic produc- known as organ- tion of energy for the cell. elles that perform specific functions. What are the three energy systems? mitochondrion A specialized cel- © Jones & Bartlett Learning,The organelle LLC of © Jones & Bartlett TheLearning, three energyLLC lular organelle responsible for the most importance in phosphagen system The energy NOT FOR SALE OR DISTRIBUTION NOT FOR SALE ORsystems DISTRIBUTION that func- aerobic production of ATP within regard to the pro- system composed of the high- tion within the the cell. duction of ATP is the energy phosphates ATP and creatine metabolic factories mitochondrion. The phosphate. It is also known as the of muscle cells to mitochondrion is sometimes more descriptively called immediate energy system. Of the prevent ATP deple- © Jonesthe &“aerobic Bartlett powerhouse Learning, of theLLC cell” because many of © Jonesthree energy& Bartlett systems, Learning,it is capable LLCtion are the phos- the metabolic pathways responsible for the aerobic pro- of producing ATP at the fastest rate. phagen system, NOT FORduction SALE of ATP OR are DISTRIBUTION found inside. Finally, each cell NOT FOR SALE OR DISTRIBUTION

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Organelles Nucleus © Jones &Endoplasmic Bartlett reticulumLearning, (ER) LLC • Contains genetic© Jones information & inBartlett the DNA Learning, LLC NOT FOR •SALE An extensive OR membrane DISTRIBUTION system extending of chromosomes.NOT FOR SALE OR DISTRIBUTION from the nuclear membrane. • Site of RNA synthesis—RNA needed • Rough ER: The outer membrane surface for protein synthesis. contains ribosomes. • Enclosed in a double-layered membrane. • Smooth ER: Devoid of ribosomes, the site of lipid synthesis. Cytoplasm Golgi apparatus © Jones & Bartlett • Enclosed Learning, in the cell LLC membrane and © Jones & Bartlett Learning, LLC • A system of stacked membrane-encased separated from the nucleus by the discs. NOT FOR SALE OR nuclear DISTRIBUTION membrane. NOT FOR SALE OR DISTRIBUTION • The site of extensive modification, sorting, • Filled with particles and organelles that and packaging of compounds for transport. are dispersed in a clear semiliquid fluid Lysosome called cytosol. • Vesicle containing enzymes that digest Cytosol intracellular materials and recycle the • The semifluid inside the cell membrane. components.© Jones & Bartlett Learning, LLC • Site of glycolysis and fatty acid synthesis.© Jones & Bartlett Learning, LLC Mitochondrion • ContainsNOT two FOR highly SALEspecialized OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION membranes, an outer membrane and a Cell Membrane highly folded inner membrane. Membranes are • A double-layered sheet, made up of lipid separated by narrow intermembrane space. and protein, that encases the cell. Inner membrane encloses space called • Controls the passage of substances in mitochondrial matrix. and out of the cell. © Jones &• OfBartlettten called theLearning, power plant of LLC the cell. • Contains receptors© Jones for hormones & Bartlett and Learning, LLC NOT FOR SALE Site where OR most DISTRIBUTION of the energy other regulatoryNOT compounds. FOR SALE OR DISTRIBUTION from carbohydrate, protein, and fat is captured in ATP (adenosine triphosphate). • About 2,000 mitochondria in a cell. Ribosome • Site of protein synthesis. © Jones & Bartlett Learning, LLC © Jones & BartlettCarbohydrate Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE ORchain DISTRIBUTION Golgi apparatus

Outer membrane Free Ribosomes Mitochondrion Inner membrane © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Mitochondrial Protein NOT FOR SALEmatrix OR DISTRIBUTIONCytosol NOT FOR SALE OR DISTRIBUTION

Nucleus

Lysosome Ribosome © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Intermembrane space Rough endoplasmic Smooth endoplasmic Mitochondrion Cell membrane reticulum reticulum © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Figure 2.22 Component parts of a NOTtypical FOR cell. SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC the anaerobic sys- how much (i.e., their anaerobic system (anaerobic aerobic system The energy sys- NOT FOR SALE OR DISTRIBUTIONtem, and the aerobic NOT FOR SALE OR DISTRIBUTIONcapacity to make glycolysis) The energy system that tem that relies upon the presence system (see Figure ATP) and how quickly has the capability to generate ATP in of oxygen to make ATP. Of the three 2.23). These three (i.e., their rate of ATP the absence of oxygen. The anaero- energy systems, it is the slowest at energy systems have production) they can bic system results in the formation producing ATP but has an almost different properties produce ATP (see © Jones & ofBartlett ATP and lactate. Learning, LLC © Jonesunending & Bartlett capacity Learning, to make ATP. LLC when it comes to Table 2.1 ). NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

9781284103465_CH02_PASS05.indd 45 08/11/16 5:51 PM 46 Section 1 The Basics of Sports Nutrition

Lactate © Jones & Bartlett Learning,BLOOD LLCMacronutrients O2 © Jones & BartlettCO 2Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE ORH2O DISTRIBUTION H+

MUSCLE CELL Macronutrient stores © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC

NOT FOR SALE ORO DISTRIBUTION2 NOT FOR SALE OR DISTRIBUTION

CO2 H2O H+ INPUT Lactate Aerobic © Jones & Bartlett Learning, LLC Energy System © Jones & Bartlett Learning, LLC Macronutrients OUTPUT NOT FOR SALE OR DISTRIBUTIONProteins NOT FOR SALE OR DISTRIBUTION Fats Anaerobic ATP Carbs Energy System Pool ATP

Phosphagen Energy System © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Figure 2.23 Metabolic factory analogy of energy metabolism.

What are the characteristics© Jones of the& Bartlett phosphagen Learning, metabolicLLC pathways to start© producing Jones &energy. Bartlett Because Learning, LLC system? NOT FOR SALE OR DISTRIBUTIONthese pathways are lengthy, NOTthere wouldFOR SALEbe a lag ORperiod DISTRIBUTION The phosphagen system is the simplest of the three before the increased production of ATP would be available. energy systems and consists of the ATP pool itself and The phosphagen system serves as an energy buffer that several other high-energy phosphates already present fills the immediate need for ATP until the other two inside the cells that can provide energy almost as quickly energy systems with higher capacities for generating ATP as ATP. The© Jones phosphagen & Bartlett system Learning, is also known LLC as the © Jones & Bartlettcan Learning, ramp up LLC their immediateNOT energy FOR system SALE because OR DISTRIBUTIONit is capable of provid- creatine phosphateNOT FOR (CP) ASALE high- ORproduction DISTRIBUTION of ATP. ing energy instanta- energy phosphate stored inside The high-energy immediate energy system The neously. For example, muscle cells. phosphates that energy system composed of the when athletes burst make up the phos- high-energy phosphates ATP and from the starting phosphocreatine A high-energy phagen energy sys- © Jonescreatine & Bartlett phosphate; Learning, as a result it isLLC blocks in a race, there © Jonesphosphate & Bartlett stored inside Learning, muscle LLCtem are the cell’s also known as the phosphagen sys- cells. It is also known as creatine NOT FOR SALE OR DISTRIBUTIONmust be an immedi- NOT FOR SALE OR DISTRIBUTIONstores of ATP (i.e., the tem. Of the three energy systems, it ate source of energy phosphate. ATP pool) and is capable of producing ATP at the available to enable another high-energy fastest rate. them to go from no molecule, called creatine phosphate (CP) or, alternatively, movement to maxi- phosphocreatine. mum speed in fractions of© a second.Jones If & ATP Bartlett was not readilyLearning, LLCCP is a high-energy phosphate© Jones that & inBartlett a one-step Learning, LLC available at the start of theNOT race, FOR then theSALE athlete’s OR DISTRIBUTIONmus- metabolic reaction can give itsNOT phosphate FOR SALE group toOR ADP DISTRIBUTION cles would have to wait for the anaerobic and aerobic to rebuild another ATP (see Figure 2.24 ). This metabolic

Table 2.1

Comparison© Jones of Characteristics & Bartlett of the Learning, Three Energy LLC Systems © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Energy system Energy system complexity Maximal rate of ATP Capacity to make ATP Lag time to increased production ATP production Phosphagen Low; one-step process Very fast Very limited None; instantaneous Anaerobic Moderate; 12-step process Fast; runs a close second Limited Seconds © JonesAerobic & Bartlett Learning,Very high; LLC many processes and Very slow;© distant Jones third & Bartlett Unlimited Learning, LLCMinutes NOT FOR SALE OR DISTRIBUTIONsteps NOT FOR SALE OR DISTRIBUTION

9781284103465_CH02_PASS05.indd 46 08/11/16 5:51 PM Chapter 2 Nutrients: Ingestion to Energy Metabolism 47

Creatine © Jones & phosphateBartlett Learning, LLCCreatine Pi © Jones & Bartlett Learning, LLC Aerobic Energy System NOT FOR SALE OR DISTRIBUTION + NOT FOR SALE OR DISTRIBUTION ATP Anaerobic Energy System Energy pool

Phosphagen System ADP © Jones & Bartlett Learning,ATP LLC © Jones & Bartlett Learning, LLC Powerful Short Burst Activity NOT FOR SALE OR DISTRIBUTION (e.g., shotNOT put, jump, FOR pitch) SALE OR DISTRIBUTION

Figure 2.24 Aerobic Energy System The ATP–CP energy system. To maintain relatively con- ATP stant ATP levels during the first few seconds of a high- Anaerobic Energy System intensity© Jones activity, & creatine Bartlett phosphate Learning, releases LLC energy and © Jones & Bartlett Learning,pool LLC its phosphateNOT FOR (Pi) toSALE regenerate OR DISTRIBUTIONATP from ADP. NOTPhosphagen FOR SALESystem OR DISTRIBUTION

Short Sprint or Activity reaction is accelerated by the enzyme creatine kinase.3 The (10 seconds of intense, all-out activity) ATP pool and the one-step creatine kinase reaction that © Jones & Bartlett Learning, LLC © Jones & BartlettAerobic Learning, Energy System LLC comprise the phos- NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION creatine kinase The enzyme that phagen energy sys- ATP Anaerobic Energy System catalyzes the reaction transferring tem give it the pool phosphate from creatine phos- highest rate of pro- Phosphagen System phate to adenosine diphosphate to duction of ATP of the make ATP. © Jones & Bartlettthree energy Learning, systems LLC © Jones & Bartlett Learning, LLC and enable it to pro- Long Sprint or Activity (1 to 3 minutes of all-out activity) vide instantaneous energyNOT to FOR the cells. SALE Its high OR rate DISTRIBUTION of ATP NOT FOR SALE OR DISTRIBUTION production makes the phosphagen energy system the one Aerobic Energy System most relied upon when energy is needed quickly during ATP very fast, powerful muscle contractions (see Figure 2.25 ). Anaerobic Energy System pool Although© Jones the & phosphagen Bartlett Learning, system can LLC supply ATP at © Jones & Bartlett Learning, LLC very high rates, it has a limited capacity to generate ATP. Phosphagen System Specifically,NOT FOR the phosphagen SALE OR system DISTRIBUTION would only be able NOT FOR SALE OR DISTRIBUTION to provide energy for 5 to 15 seconds, depending on the Long Duration, Non-Steady-State Activity intensity of the activity.4 As a result, it needs assistance (4 to 6 minutes, all-out activity) from the other energy systems. Aerobic Energy System © Jones &What Bartlett are the Learning, characteristics LLC of the anaerobic © Jones & Bartlett Learning, LLC ATP NOT FOR SALE OR DISTRIBUTION NOT FOR SALEAnaerobic OR DISTRIBUTION Energy System and aerobic energy systems? pool As mentioned earlier, unlike the phosphagen system, which is basically an inventory of readily available high- Phosphagen System energy phosphates within cells, the anaerobic and aerobic energy systems must© Jones generate & ATP Bartlett via more Learning, complex LLC Long Duration, Steady-State© Jones Aerobic & Bartlett Activity Learning, LLC cellular processing (see Table 2.1). As a result, there is a (30 minutes of continuous activity) slight lapse in time beforeNOT the FOR aerobic SALE and anaerobicOR DISTRIBUTION sys- NOT FOR SALE OR DISTRIBUTION tems can ramp up and begin contributing ATP when an Figure 2.25 The three energy systems work together to meet the activity begins or changes in intensity. Compared to the energy demands of any level of physical activity. Width of phosphagen system, the anaerobic energy system is not arrow along with gray shading denote degree and source quite as fast at producing ATP, but it has a slightly higher © Jones & Bartlett Learning, LLC of energy© contribution.Jones & Bartlett Learning, LLC capacity to make more ATP. In contrast, the aerobic energy NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION system has an unlimited capacity to make ATP and far How do the energy systems work together exceeds the phosphagen and anaerobic systems in this characteristic. However, because it is a complex system, to supply ATP during sport performance? its rate of ATP production is much slower than the other During sports, the energy requirement of muscle is © Jones &two. Bartlett In short, Learning, each energy LLC system has different charac©- Jonesrelated & Bartlett to the intensity Learning, and LLCduration of the activity. In teristics that help to satisfy our body’s energy needs no other words, slow movements do not require ATP to be NOT FORmatter SALE what OR the DISTRIBUTION activity. NOT FORsupplied SALE as rapidly OR DISTRIBUTION as more powerful, fast movements do.

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© JonesAs discussed & Bartlett earlier, Learning, the existing LLC ATP pool in muscle cells © Jonesand anaerobic & Bartlett systems Learning, would have LLC to help fill the slight is very small. Therefore, it is imperative that the three energy deficit. However, the energetic demand placed on NOT FORenergy SALE systems OR work DISTRIBUTION together to maintain ATP levels. NOTthe FOR phosphagen SALE ORand DISTRIBUTIONanaerobic systems would be rela- Remember, muscle cells never run out of ATP. Thus, if tively low, and the runner could maintain this increased an activity is so intense and burns ATP so quickly that pace for approximately a mile or two before fatigue sets the three energy systems cannot supply ATP fast enough in. However, if the marathoner decided to sprint as fast as to prevent ATP depletion,© fatigueJones ensues & Bartlett (Figure Learning, 2.21). possible,LLC then the all-out sprint© Jones would require& Bartlett ATP to Learning, be LLC Fatigue causes a decrease in the level of activity, result- supplied at rates well above the aerobic system’s ability ing in a lower energy demand,NOT therebyFOR SALE giving theOR energy DISTRIBUTION to supply it. In this scenarioNOT the muscles FOR SALE would haveOR DISTRIBUTIONto systems a chance to begin replenishing the level of ATP. rely much more heavily on the other two energy systems, To prevent fatigue and maintain ATP levels above and exhaustion would set in much more quickly. If the the threshold for fatigue, the energy systems must work marathoner timed the final sprint just right, sprint speed together, ©taking Jones advantage & Bartlett of their Learning, unique characteristics LLC could be maintained© Jones for &approximately Bartlett Learning, 200 meters LLC before to meet the metabolic demands for ATP. Of the three energy the muscles’ ATP stores fell to critically low levels. Recall systems, NOTthe muscle FOR cells SALE rely predominantlyOR DISTRIBUTION on the aero- that when ATPNOT levels FOR get lowSALE exhaustion OR DISTRIBUTION sets in (see Fig- bic system because of its unending ability to make ATP. If ure 2.21). Sprinting places a huge demand on the phos- the energy requirements of an activity are low enough for phagen and anaerobic energy systems, and, as a result, the aerobic energy system to meet the energy demands, regular sprint training causes muscles to adapt. The mus- © Jonesexercise & Bartlett can be continued Learning, for a LLC long duration. This results © Jonescles increase & Bartlett their stores Learning, of ATP andLLC CP. In addition, the NOT FORin a conditionSALE OR called DISTRIBUTION steady state exercise, where the NOTmuscle FOR cells SALE make OR more DISTRIBUTION enzymes such as creatine kinase energy demands are and others associated with anaerobic metabolism. The steady state exercise Any level being met primarily end result is a sprint athlete who can maintain his or or intensity of physical activity in by the aerobic system her maximum running speed for fractions of a second which the energy demand for ATP (see Figure 2.25e). The longer than the competition and thus perhaps win the is met by the aerobic production© Jones more & Bartlett highly trainedLearning, race.LLC Creatine monohydrate ©is aJones dietary supplement& Bartlett thatLearning, LLC of ATP. NOT FORthe SALE aerobic OR energy DISTRIBUTION NOT FORincreases SALE the OR levels DISTRIBUTION system, the faster a creatine monohydrate A dietary of CP in the muscle, person can move while remaining in a steady state. supplement that can help improve and thus is a popular Endurance athletes train every day to challenge and an athlete's anaerobic strength and item with sprint and improve the aerobic systems of their muscle cells. Their power by increasing levels of cre- power athletes.5 Cre- muscles ©respond Jones to & the Bartlett daily demands Learning, by increasingLLC atine phosphate© Jones in muscles. & Bartlettatine Learning, monohydrate LLC the cellularNOT organelles FOR SALE where ORaerobic DISTRIBUTION production of ATP NOT FOR SALE ORbolsters DISTRIBUTION the immedi- occurs: the mitochondria. As mentioned earlier, increas- ate energy system’s ability to supply ATP, thus delaying ing the number and size of mitochondria enables the fatigue in high-intensity activities.6,7 cell to greatly increase the speed with which it makes Athletes with energy needs somewhere between ATP. Because ATP can be supplied much more rapidly, the those of the sprinter and those of the marathoner rely © Jonesspeed & ofBartlett the activity Learning, can be performed LLC more quickly while © Joneson the three& Bartlett energy Learning,systems working LLC together. The reli- the athlete remains in a steady state. This is why highly ance on each of the systems depends on the nature of NOT FORtrained SALE marathoners OR DISTRIBUTION can run 26.2 miles at speeds that NOTthe FOR sport. SALE In other OR words, DISTRIBUTION there exists an energy con- untrained persons could not run for even 1 mile without tinuum (see Figure 2.26 ). The energy required for various fatiguing. sports activities When the energy needs of the muscle cannot be energy continuum A continuum falls at different of activity levels spanning from low- met by the aerobic system,© Jones the other & twoBartlett systems Learning, are LLC © Jonespoints & Bartlettalong this Learning, LLC needed to supplement the deficiency in ATP. If the activ- est to maximum, with all points in energy continuum. ity is just slightly above NOTthe ability FOR of SALE the aerobic OR DISTRIBUTION sys- between requiring slightly increasNOT- FORFor example,SALE OR anDISTRIBUTION tem to supply ATP, then the amount supplemented by ing rates of energy production. athlete who runs the other two systems is low, and the activity can be the mile moves at continued for quite a while before fatigue sets in (see speeds somewhere between those of the sprinter and Figure 2.25d).© Jones As the & intensity Bartlett of Learning, the activity LLCincreases, those of the© marathoner Jones & Bartlett(see Figure Learning, 2.25d). The LLC inten- the ability to produce energy through the aerobic path- sity of the miler’s run is higher than that which can be ways decreases,NOT FOR and thereforeSALE OR the DISTRIBUTION reliance on the other provided byNOT the aerobic FOR SALEsystem ORbut not DISTRIBUTION so intense that two systems increases, causing fatigue to ensue more it puts a huge demand on the phosphagen system. In quickly. For example, if a marathoner decided to increase this case the anaerobic system plays a larger role in her running speed to something faster than her normal working with the aerobic system to provide the needed © Jonesrace & pace, Bartlett the demand Learning, for ATP LLC production would go up. © JonesATP. The & bottomBartlett line Learning, is that any LLC activity relies on the If the increase in speed was slightly above the aerobic optimal blending of energy production by the three NOT FORsystem’s SALE ability OR to DISTRIBUTION supply ATP, then the phosphagen NOTenergy FOR systems SALE (seeOR FigureDISTRIBUTION 2.26).

9781284103465_CH02_PASS05.indd 48 08/11/16 5:51 PM Chapter 2 Nutrients: Ingestion to Energy Metabolism 49

100 100 © Jones & Bartlett Learning, LLC © JonesWhat & Bartlett metabolic Learning, pathways LLC are involved Phosphagen NOT FORwith SALE the energy OR DISTRIBUTION systems? NOT FOR SALE OR DISTRIBUTIONsystem The phosphagen system does not involve any metabolic Aerobic pathways because its function is based on already exist- system ing stores of high-energy phosphates. The cellular processing required to make ATP anaerobically or aerobically 1 ©23 Jones & Bartlett4 Learning, LLCoccurs via metabolic pathways© Jones. Metabolic & Bartlett pathways Learning, can LLC NOT FOR SALE OR DISTRIBUTION NOT FORbe SALE anabolic OR DISTRIBUTIONpath- metabolic pathways Sequentially ways, which require Anaerobic

rcent ATP Supplied ATP rcent energy and result system organized metabolic reactions that Pe are catalyzed by enzymes and result in the formation of more complex mol- © Jones & Bartlett Learning, LLC in the formation© Jones or breakdown& Bartlett of Learning, LLC chemicals within the body. ecules, or catabolic NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTIONpathways, which anabolic pathway A metabolic release energy and 0 0 pathway that requires energy and result in the break- Low ModerateHighVery High results in the formation of more down of molecules Exercise Intensity complex molecules. (see Figure 2.27 ). The © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC anaerobic and aero- NOT FORFigure SALE 2.26 OR DISTRIBUTION NOT FORcatabolic SALE pathway OR DISTRIBUTIONA metabolic bic metabolic path- ATP contribution of the three energy systems to maximally pathway that degrades complex ways are catabolic. sustained activities of very short, high-intensity exercise, compounds into simpler ones and In short, anaerobic such as the shot put (i.e., right margin of graph), to low- in the process gives off energy. and aerobic meta- intensity maximally sustained exercise lasting longer than bolic pathways are 3 minutes, such as running© Jones a marathon & Bartlett (i.e., left Learning,margin). LLC © Jones & Bartlett Learning, LLC sequential steps in which foods (i.e., carbohydrates, fats, Note: The longer the duration of ”maximally sustained NOT FOR SALE OR DISTRIBUTIONand proteins) are brokenNOT down FOR (see SALETables 2.2 OR and DISTRIBUTION 2.3 ). activity,” the lower the exercise intensity. Area 4 spans from In other words, these metabolic pathways are assembly fractions of a second to 30 seconds, area 3 spans from 30 lines in reverse (i.e., disassembly lines). Instead of build- seconds to 1.5 minutes, area 2 spans from 1.5 minutes to 3 ing something in a stepwise systematic fashion, meta- minutes, and area 1 is for time longer than 3 minutes. © Jones & Bartlett Learning, LLC bolic pathways© Jones slowly & Bartlett break apart Learning, food molecules LLC in an NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

Catabolic Reactions

NOT FOR SALE OR DISTRIBUTION Glucose GlycerolNOT FattyFOR acids SALEAmino OR acids DISTRIBUTION

Energy Energy Energy Energy

Aanbolic Reactions © Jones & Bartlett Learning,Glucose++ GlucoseLLC Glycerol Fatty acids Amino© Jones acid+ Amino & acidBartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Energy Energy Energy

Glycogen Triglyceride Protein

© Jones &Figure Bartlett 2.27 Learning, LLC © Jones & Bartlett Learning, LLC Catabolism and anabolism. Catabolic reactions break down molecules and release energy and other products. Anabolic NOT FORreactions SALE consumeOR DISTRIBUTION energy as they assemble complex molecules.NOT FOR SALE OR DISTRIBUTION

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Unlike the phosphagen system, which at its longest is © JonesTable & Bartlett2.2 Learning, LLC © Jones & Bartlett Learning, LLC one step, the anaerobic system involves a metabolic path- NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Metabolic Pathways Associated with the Three Energy way (i.e., glycolysis) of 12 steps. Because it is lengthier and Systems more complex than the phosphagen system, it is a little slower to adapt to changes in activity level. However, it Phosphagen Anaerobic Aerobic is much faster to adapt than the aerobic energy system, Metabolic None Glycolysis Beta-oxidation which is the slowest of the three systems. The anaerobic pathways © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC energy system is a major contributor to intense (i.e., maxi- NOT FORGlycolysis SALE OR DISTRIBUTIONmal effort) activities that lastNOT from FOR 1 to 3SALE minutes OR (see DISTRIBUTION Deamination Figure 2.25c). During these activities, oxygen availability Citric acid cycle is limited because of the intense muscle contractions that Electron transport chain close off blood vessels and limit delivery of oxygen, at © Jones & Bartlett Learning, LLC least in large© enough Jones quantities & Bartlett to completely Learning, meet LLC the energy demands of the activity. NOT FOR SALE OR DISTRIBUTION AlthoughNOT the anaerobicFOR SALE system’s OR rateDISTRIBUTION of production Table 2.3 of ATP is fairly high, its capacity for making ATP is limited (see Table 2.1). During intense exercise, hydrogen ions are Energy Nutrients and the Sequence of the Aerobic released and accumulate in the muscle cells due to the Metabolic Pathways That Metabolize Them for Energy © Jones & Bartlett Learning, LLC © Jonesrapid breakdown & Bartlett of ATP. Learning, The buildup LLC of hydrogen ions and Carbohydrates Fats Proteins NOT FOR SALE OR DISTRIBUTION NOTthe FOR acidic SALE condition OR itDISTRIBUTION causes interferes with the activ- Glycolysis 1 ity of key glycolytic enzymes and mechanisms of muscle Beta-oxidation 1 contraction thus causing fatigue. To experience the fatigue Deamination 1 caused by hydrogen ion build-up, one only needs to run around an outdoor track as fast as possible. The burning Citric acid cycle 2 2 2 feeling experienced in the muscles is caused by the acidic Electron transport chain © Jones3 & Bartlett3 Learning, 3 LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTIONcondition that results from hydrogenNOT FOR ion build-up.SALE OR DISTRIBUTION Compared to the other energy systems, the aerobic system is the slowest at producing ATP, but it has an organized stepwise order. This helps the cells to cap- unlimited ability to make ATP. The aerobic system pro- ture as much energy as possible from foods to make ATP. vides the fuel for resting metabolic needs. It also is the Although© there Jones is some & Bartlett commonality Learning, in the LLCmetabolic energy system© Jonesmost relied & Bartlettupon for longer Learning, duration, LLC con- pathways required to break down carbohydrates, fats, NOT FOR SALE OR DISTRIBUTION tinuous activitiesNOT thatFOR can SALE be performed OR DISTRIBUTION for minutes to and proteins, there are a couple pathways that are unique hours. The aerobic energy system is also the longest and depending on the energy nutrient being processed and/or most complex of the three energy systems (see Table 2.1). the availability of oxygen. It involves five different metabolic pathways (see Table The anaerobic energy system (see Figure 2.28 ), involves 2.2). The metabolic pathways involved depend on the one metabolic pathway called anaerobic glycolysis. The © Jones & Bartlett Learning, LLC © Joneschemical & Bartlettstructure Learning,of the food moleculeLLC being broken only macronutrient that can be broken down via glycol- down (see Table 2.3 and Figure 2.29 ). The end products of NOT FORysis is SALE carbohydrates. OR DISTRIBUTION Glycolysis is unique in that it can NOTthe FOR aerobic SALE energy OR system DISTRIBUTION are ATP, carbon dioxide, and be part of both the water. It should be noted that carbon dioxide and water glycolysis A metabolic pathway anaerobic and aero- are the very same molecules used by plants to make car- that is responsible for the break- bic energy systems. bohydrates, along with fats and proteins. In short, plants down of glucose. It is unique in that When adequate © Jones & Bartlett Learning,use LLC carbon dioxide from the ©air, Jones water from & Bartlett the soil, andLearning, LLC it can function with or without the amounts of oxygen light energy from the sun to make the energy nutrients. presence of oxygen. NOT FORare SALE not available OR DISTRIBUTION and During aerobic metabolism ourNOT cells FOR break SALE the foods OR back DISTRIBUTION energy is needed, the down to their constituent parts of carbon dioxide and end product of glycolysis (i.e., pyruvate) is converted to water, thus releasing the chemical energy in the foods lactate (see Figure 2.28). This last step or reaction enables (see Figure 2.28) and using it to make ATP. The carbon glycolysis to continue producing ATP without the need © Jones & Bartlett Learning, LLC dioxide and© water Jones released & Bartlett from the Learning, body can thenLLC be for oxygen, which is why it is called the anaerobic energy reused by plants to make more energy nutrients, thus NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION system. Anaerobic means without oxygen. Alternatively, completing the ongoing energy cycle. if oxygen is present, anaerobic A term used to describe then pyruvate is not What pathways are associated with the aerobic a condition in which oxygen is not converted to lactate. breakdown of carbohydrates? present. Instead, it is metabo- The first metabolic pathway carbohydrates must pass © Jones & Bartlett Learning, LLC lized in other meta- © Jonesthrough & is theBartlett glycolytic Learning, pathway (see LLC Figure 2.28). When suf- NOT FORbolic pathwaysSALE OR that DISTRIBUTION are associated with the aerobic energy NOTficient FOR oxygen SALE is present, OR DISTRIBUTION pyruvate, which is the end product systems discussed in the following section. of glycolysis, is converted to acetyl coenzyme A (acetyl CoA)

9781284103465_CH02_PASS05.indd 50 08/11/16 5:51 PM Chapter 2 Nutrients: Ingestion to Energy Metabolism 51

ATP ay © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTIONADP One w NOT FOR SALE OR DISTRIBUTION

NOT FOR SALE OR DISTRIBUTIONADP One w NOT FOR SALE OR DISTRIBUTION

H+ + NADH NADH + H+

ADP ADP

ATP ATP © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

ATPAOne w One w TP NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

Lactate Lactate Pyruvate Pyruvate

Figure 2.28 Anaerobic glycolysis. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION (see Figure 2.30 ) rather from the molecules pyruvate The end product of than converted to nicotinamide adenine dinucle- as they pass through. glycolysis. lactate as during otide (NAD) One of two electron The stripped hydro- anaerobic metabo- carriers that is responsible for shut- gens are picked up by citric© acidJones cycle &One Bartlett of the major Learning, LLC © Jones & Bartlett Learning, LLC lism. The acetyl CoA tling hydrogens from one metabolic special carrier mol- metabolic pathways of the aerobic NOT FOR SALE OR DISTRIBUTIONthen enters into the step or NOTpathway FOR to another. SALE OR DISTRIBUTIONecules known as nic- energy system. It is also known as citric acid cycle (see otinamide adenine the Krebs cycle or the tricarboxylic Figure 2.31 ), which is flavin adenine dinucleotide dinucleotide (NAD) acid cycle. Its main role is to strip a series of reactions (FAD) One of two electron carri- and flavin adenine hydrogens from compounds pass- that occur inside of ers that is responsible for shuttling dinucleotide (FAD). © Jones & ingBartlett through it.Learning, LLC © Jones & Bartlett Learning, LLC the mitochondria hydrogens from one metabolic step NAD and FAD com- NOT FOR SALE OR DISTRIBUTION of the cell. The priNOT- FORor pathwaySALE to OR another. DISTRIBUTIONbine with the stripped mary purpose of the citric acid cycle is to strip hydrogens hydrogens to form

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FATS CARBOHYDRATES PROTEINS The hydrogen transfer molecules associated with the © Jones & Bartlett Learning, LLC © Joneselectron & transport Bartlett chain Learning, are located LLC on the inner mem- NOT FOR SALE OR DISTRIBUTION NOTbrane FOR of theSALE mitochondria. OR DISTRIBUTION The transfer of hydrogens down Fatty acids Glucose Amino acids the ETC begins once the hydrogen carriers NADH and FADH release their hydrogens to the ETC (see Figure 2.32). The Glycolysis resulting NAD and FAD are available to cycle back to the citric acid cycle to pick up more hydrogens. The hydrogens Beta © Jones & DeaminationBartlett Learning, LLC © Jones & Bartlett Learning, LLC oxidation Pyruvate dumped into the ETC are transferred from one transfer NOT FOR SALE OR DISTRIBUTIONmolecule to another. In the processNOT FOR of hydrogen SALE transfer, OR DISTRIBUTION energy is given off and captured in the form of ATP. The e– final acceptor molecule for the hydrogens being passed Acetyl CoA down the ETC is oxygen, which results in the formation of © Jones & Bartlett Learning, LLC water (see Figure© Jones 2.32). The & Bartlett ETC is the Learning, metabolic pathway LLC that generates the most ATP during aerobic metabolism. NOT FOR SALECitric OR DISTRIBUTION The problemNOT is that FOR the ETC SALE is the finalOR pathwayDISTRIBUTION in aerobic e– acid metabolism, and as a result, it takes time for ATP formation cycle to increase in response to exercise or activity. The citric acid cycle and the electron transport chain © Jones & Bartlett Learning, LLC © Jonesare aerobic & Bartlett pathways Learning, that are common LLC to all three energy Electron transport chain nutrients. As already noted, both of these metabolic path- NOT FOR SALE OR DISTRIBUTION NOTways FOR are SALEfound in OR the DISTRIBUTION mitochondria of the cells. For this reason, mitochondria are called “aerobic powerhouses” of ATP the cells. Endurance-type training challenges these metabolic pathways to produce energy more rapidly. The cells © Jones & Bartlett Learning, adaptLLC to endurance training© by Jones increasing & Bartlett the size andLearning, LLC Figure 2.29 number of mitochondria, allowing for greater production Aerobic metabolism of theNOT macronutrients. FOR SALE OR DISTRIBUTIONof ATP aerobically.8 This is oneNOT of the FOR reasons SALE why ORendur DISTRIBUTION- ance athletes can perform at higher intensities for a lon- NADH and FADH, ger duration than untrained persons. electron transport chain respectively. The (ETC) The© final Jones metabolic & Bartlettpathway Learning,attached hydrogensLLC © Jones & Bartlett Learning, LLC What pathways are associated with the aerobic of the aerobicNOT energy FOR system. SALE It isOR DISTRIBUTIONare transported to the NOT FOR SALE OR DISTRIBUTION responsible for transferring hydrogens final aerobic pathway, breakdown of fats and proteins? from one chemical to another and in the electron trans- Fats and proteins cannot be metabolized via glycolysis the process making ATP and water. port chain (ETC) (see and therefore must pass through other pathways before Figure 2.32 ). entering into the citric acid cycle and ETC (see Figure 2.29). © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC

NOT FOR SALE OR DISTRIBUTIONGlucose NOT FOR SALE OR DISTRIBUTION

Pyruvate Lactate When limited oxygen is available, pyruvate is Acetyl CoA e– shunted to form lactate. Citric

e cycle

c t NOTr FOR SALE OR DISTRIBUTION Lactate NOT FOR SALE OR DISTRIBUTION o n

tr an Pyruvate sport chain NAD+

e– e– Coenzyme A + © Jones & Bartlett Learning, LLCH + NADH One way © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION When oxygen is readily available To electron CO2 and energy is needed, pyruvate is transport chain CoA converted to acetyl CoA. Acetyl CoA © JonesFigure & Bartlett2.30 Learning, LLC © Jones & Bartlett Learning, LLC NOT FORPyruvate SALE to acetyl OR CoA.DISTRIBUTION When oxygen is readily available, eachNOT pyruvate FOR formedSALE from OR glucoseDISTRIBUTION yields one acetyl CoA and one NADH.

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Oxaloacetate e– e– e– + e– NADH + H Citric © Jones & Bartlett Learning,Citrate (citric LLCacid) © Jones– & Bartlett Learning, LLC e acid NOT FOR SALE OR DISTRIBUTION NOT FOR SALEcycle OR DISTRIBUTION

+ E l NAD e c

t r o n

tr an sp ort chain Citric acid cycle NAD+ CO2 © Jones & Bartlett Learning, LLC e©– eJones– & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOTNADH +FOR H+ SALE OR DISTRIBUTION

CO2 e– e– NAD+ FADH2 e– e– © Jones & Bartlett Learning, LLC © JonesNADH & +Bartlett H+ Learning, LLC FAD NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION GTP GDP + Pi

To electron transport chain To electron transport chain © PJonesi + ADP & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC ATP NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Figure 2.31 The citric acid cycle. This circular pathway conserves carbons as it accepts one acetyl CoA and yields two CO2, three NADH, one FADH2, and one guanosine triphosphate (GTP), a high-energy compound that can be readily converted to ATP. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Fats mustNOT first FOR be SALEmetabolized OR DISTRIBUTIONvia beta-oxidation, which the ETCNOT to produce FOR SALEATP (see OR Figure DISTRIBUTION 2.29). However, it is a cyclical pathway that is found within the confines of should be noted that proteins are not normally a major the mitochondria. source of energy (they provide less than 10% of energy for beta-oxidation The first meta- Each pass of a fatty exercise) unless energy expenditure is high and/or car- bolic pathway of fat metabolism, acid through beta- bohydrate intake is low.9 © Jones & whichBartlett cleaves Learning, off two carbon LLC mol- oxidation cleaves ©off Jones &When Bartlett diets areLearning, low in carbohydrates LLC or when an ath- NOT FOR SALEecules each OR time DISTRIBUTION a fatty acid chain two carbon fragNOT- FORlete isSALE involved OR in DISTRIBUTION training that depletes carbohydrate cycles through it. ments from the end stores, the body must get its carbohydrates from some- of the fatty acids. where else. It does so by converting proteins in the body Each pass also results in the formation of an NADH and to carbohydrates in a process known as gluconeogenesis an FADH. The two carbon fragments are converted to ace- (see Figure 2.34 ). Dur- tyl CoA, which then enters© Jones the citric & Bartlett acid cycle Learning, and ulti- LLCgluconeogenesis The formation© Jones ing& Bartlett gluconeogenesis, Learning, LLC mately the ETC. TheNOT NADH FOR and SALE FADH transferOR DISTRIBUTION their of glucose from noncarbohydrateNOT FORproteins SALE areOR broken DISTRIBUTION hydrogens to the ETC for use in ATP production. sources such as proteins. down into amino Proteins contain nitrogen components in their acids, transported to molecular structure. These nitrogen-containing compo- the liver, and con- nents cannot be used by the body and thus must first be Gaining the verted to the car- cleaved© Jones from the & protein Bartlett before Learning, it can be metabolized LLC for © PerformanceJones & Bartlett Edge Learning,bohydrate LLC glucose, energy.NOT The FOR process SALE in which OR the DISTRIBUTION nitrogen group is cleaved NOT FOR SALE OR DISTRIBUTIONwhich can then be from proteins is called deamination (see Figure 2.33 ). Carbohydrates spare muscle pro- used for energy by Once the nitrogen is tein by decreasing the body's reli- the body tissues. ance on gluconeogenesis to make deamination The metabolic path- removed, the Unfortunately for its own carbohydrates. way that is responsible for removing remaining carbon the athlete, most of © Jones & theBartlett nitrogen Learning,or amine group LLC from molecule can pass© Jones & Bartlett Learning, LLC the proteins used in NOT FOR SALEthe carbon OR structure DISTRIBUTION of amino acids. through the citricNOT FORgluconeogenesis SALE OR comeDISTRIBUTION from muscle.10 This is one reason acid cycle and then why carbohydrate intake is so important to the athlete.

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Outer mitochondrial © Jones & Bartlettmembrane Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

Cytosol © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALEOuter OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION mitochondrial membrane

Inner Electron transport chain mitochondrial e– e– e– e– membrane

– – – – © Jones &e Bartlette Learning,e e LLC ADP + Pi © Jones & Bartlett Learning, LLC + NOT FOR NADHSALE+ OR H FADHDISTRIBUTION2 NOT FOR SALE OR DISTRIBUTION 1 ATP ⁄2O2 H2O

NAD+ FAD Oxygen accepts the energy-depleted electrons and reacts with hydrogen © Jones & Bartlett Learning,Mitochondrial LLC matrix to form water. © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Figure 2.32 Electron transport chain. This pathway produces most of the ATP available from glucose, as well as fats and amino acids. Mitochondrial NADH delivers pairs of high-energy electrons to the beginning of the chain. Each of these NADH molecules ultimately produces 2.5 ATP. The pairs of high-energy electrons from FADH2 enter this pathway farther along, so one © JonesFADH2 & Bartlettproduces 1.5Learning, ATP. LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION If carbohydrate intake R Food for Thought 2.2 O is adequate to meet energy demands and Understanding Bioenergetics HNCOC H © Jones & Bartlett Learning,carbohydrate LLC stores In this© Jonesexercise, &your Bartlett knowledge Learning, LLC H H are replenished after NOT FOR SALE OR DISTRIBUTION of howNOT the FOR energy SALE systems ORwork DISTRIBUTION training, then pro- together to supply ATP during The liver converts teins do not need activity will be challenged. the amino group to be converted to to ammonia and R then to urea. carbohydrates, and O © Jones & Bartlett Learning, LLC muscle protein© Jones is & Bartlett Learning, LLC O COC H spared. The relation- Food for Thought 2.3 NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION ship between carbo- You Are the Nutrition Coach The structure of the remaining hydrate intake and carbon skeleton determines where Apply the concepts from this it can enter the energy-producing protein breakdown pathways. for energy is a criti- chapter to several case studies. © Jones & Bartlett Learning, LLC © Jonescal concept & Bartlett to under -Learning, LLC Figure 2.33 stand. Put in other words, adequate carbohydrates in the NOT FORDeamination. SALE ORA deamination DISTRIBUTION reaction strips the amino NOTdiet FOR spare SALE muscle OR protein. DISTRIBUTION group from an amino acid.

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NADH + H+ ADP © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOTATP FOR SALE OR DISTRIBUTION

Lactate Pyruvate Some amino acids

GDP © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE ORGTP DISTRIBUTIONATP NOT FOR SALE OR DISTRIBUTION

ADP Acetyl CoA CoA

Citric acid cycle © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FORSome SALE amino acids OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

Figure 2.34 Gluconeogenesis. Liver and kidney cells make glucose from pyruvate by way of oxaloacetate. Gluconeogenesis is not the © Jones &reverse Bartlett of glycolysis. Learning, Although LLC these pathways share many© Jones reactions, & albeitBartlett in the Learning, reverse direction, LLC gluconeogenesis NOT FORmust SALE detour OR around DISTRIBUTION the irreversible steps in glycolysis. NOT FOR SALE OR DISTRIBUTION

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nn The digestive system is basically a long, internal- responsible for the entrance and exit of fats from the ized tube that passes© through Jones the & body.Bartlett Foods Learning, enter LLCadipocytes. © Jones & Bartlett Learning, LLC via the mouth and exit from the anus. Substances nn Fatty acids in the blood are transported into muscle in the digestive systemNOT have FOR not SALEentered OR the DISTRIBUTIONbody cells via facilitated diffusion,NOT whereasFOR SALE triglycerides OR DISTRIBUTION until they are absorbed across the intestinal wall. in bloodborne chylomicrons are acted upon by lipo- nn The anatomy of the digestive system includes the protein lipase in the capillaries found in muscle. mouth, esophagus, stomach, small intestine, and Lipoprotein lipase breaks down the triglycerides into large© intestine. Jones &Associated Bartlett Learning,structures, LLCincluding fatty acids,© Jones which are& Bartlett then transported Learning, across LLC the the salivary glands, pancreas, liver, and gallblad- muscle cell membrane. Once inside the muscle cells, der, secreteNOT FOR enzymes SALE and ORbile DISTRIBUTIONsalts that help in the the fats NOTcan be FOR stored SALE or used OR for energy.DISTRIBUTION digestive process. nn During digestion, dietary proteins are broken into nn Digestion of carbohydrates begins in the mouth as their basic building blocks, known as amino acids. a result of the mechanical process of mastication nn Digestion of proteins begins in the mouth via mas- © Jones &and Bartlett the enzymatic Learning, actions LLC of salivary amylase. How- © Jonestication & Bartlett and continues Learning, in the LLC stomach where they ever, the majority of digestion occurs in the small are denatured by hydrochloric acid. Once they leave NOT FORintestine, SALE ORwhere DISTRIBUTION the foodstuffs are subjected to the NOT FORthe stomach,SALE OR protease DISTRIBUTION enzymes in the small intes- actions of various pancreatic and intestinal enzymes. tine continue to break the proteins into single amino nn During digestion, carbohydrates are broken down acids or small chains of two or three amino acids. into their component parts, monosaccharides (i.e., nn The small digested protein remnants are absorbed via simple sugars). © Jones & Bartlett Learning, LLCfacilitated diffusion or active© Jones transport & Bartlett in the small Learning, LLC nn Absorption of monosaccharides occurs in the small intestine. Once inside the intestinal cells, any exist- intestine via facilitatedNOT diffusion FOR or SALE active ORtransport, DISTRIBUTION ing chains of amino acidsNOT are brokenFOR SALE up into OR single DISTRIBUTION depending on the type of sugar. amino acids and then released into the bloodstream. nn Once the bloodborne simple sugars reach the cells nn When ingested amino acids make it into the blood- of the liver, those that are not in the form of glucose stream, they become part of the body’s amino acid (e.g., ©fructose) Jones are & convertedBartlett Learning,to glucose. The LLC glucose pool. The© amino Jones acid & poolBartlett also includes Learning, amino LLC acids can then be stored as glycogen in the liver cells or found in other tissues, primarily skeletal muscle releasedNOT back FOR into SALE the bloodstream OR DISTRIBUTION to be used for and theNOT liver. TheFOR blood, SALE with OR its DISTRIBUTION circulating levels energy or stored by other cells of the body. of amino acids, makes up the central part of the nn Digestion of dietary fats begins in the mouth via amino acid pool, which remains in equilibrium with mastication and the enzymatic actions of salivary the other compartments. This helps to maintain the © Jones &lipase. Bartlett The digestive Learning, process LLC continues in the stom- © Jonesblood’s & Bartlett levels of Learning, amino acids, LLC thereby serving as a ach through muscle actions of the stomach wall and constant and readily available source of amino acids NOT FORthe SALE enzymatic OR DISTRIBUTIONactions of gastric lipase. However, the NOT FORfor the SALE body. OR DISTRIBUTION majority of fat digestion occurs in the small intes- nn Amino acid absorption from the bloodstream into tine, where various lipases act on the dietary fats the cells of the body tissues occurs through facili- (i.e., triglycerides), breaking them into free fatty tated diffusion. Once inside, the amino acids can acids and monoglycerides.© Jones & Bartlett Learning, LLCbe used to make needed© proteins Jones through& Bartlett the pro Learning,- LLC nn Absorption of fats also occurs in the small intes- cesses of transcription and translation. Genes in the tine. The short- and NOTmedium-chain FOR SALE fatty ORacids DISTRIBUTION are nucleus are transcribed NOTto form FOR mRNA. SALE The ORmRNA DISTRIBUTION absorbed via passive diffusion and enter directly leaves the nucleus and is translated by ribosomes, into the bloodstream. Long-chain fatty acids and which attach the amino acids together to form the monoglycerides are wrapped by bile salts to form specific protein required. micelles© Jones and carried & Bartlett to the Learning,intestinal wall, LLC where nn Minerals,© vitamins,Jones & and Bartlett water Learning,do not need LLC to be the fats are released from the micelles and absorbed broken down into smaller units via digestion to be via passiveNOT FOR diffusion. SALE The OR absorbed DISTRIBUTION fats from the absorbedNOT into theFOR body. SALE OR DISTRIBUTION micelles are resynthesized into triglycerides and nn Digestion of food releases minerals and vitamins, packaged into chylomicrons. The chylomicrons are thereby making them available for absorption. Most released from the cells and enter into the circulatory vitamins and minerals are absorbed in the small © Jones &system Bartlett via the Learning, lymph. LLC © Jonesintestine. & Bartlett The exceptionsLearning, are LLC sodium, potassium, nn Lipoprotein lipase, which is located on capil- chloride, and some vitamin K, which are all absorbed NOT FORlary SALE walls OR and DISTRIBUTION inside adipocytes, is the enzyme NOT FORin the SALE large intestine. OR DISTRIBUTION

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© Jones n&n BartlettWithout knowledgeLearning, of LLC the three energy systems and© Jones &from Bartlett rest toLearning, maximal LLCphysical movements, the how they work together to supply energy during three energy systems work together to maintain the NOT FOR SALEspecific OR sports DISTRIBUTION activities, the sports nutrition profesNOT- FOR ATPSALE levels. OR ATP DISTRIBUTION levels are never depleted in cells; sional is severely disadvantaged with regard to cre- if the energy systems cannot keep up with energy ating an individualized dietary plan. demand, fatigue occurs. The decrease in perfor- nn Energy is an entity that is better explained or defined mance caused by fatigue lowers energy demand and than shown because© Jones it has no& shape,Bartlett no describableLearning, LLC enables the energy ©systems Jones to & prevent Bartlett ATP Learning, deple- LLC features, and no physical mass. Energy enables ath- tion. NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION letes to perform physical work and is measured in nn To metabolize the energy nutrients and in the pro- kilocalories (kcals). All cellular and bodily functions cess make ATP, the cells must possess enzymes that require energy. The sum total of all the energy (i.e., sequentially break down the energy nutrients and in total daily calories) required by the body to power cel- the process capture energy in the form of ATP. The lular© Jones processes & andBartlett activities Learning, is known asLLC metabolism. enzymes© Jones for the & phosphagen Bartlett Learning, and anaerobic LLC systems nn Energy exists in six basic forms: chemical, nuclear, lie within the cytoplasm of the cell. The majority electrical,NOT FOR mechanical, SALE OR thermal, DISTRIBUTION and radiant. How- of enzymesNOT FOR and SALEmolecular OR compounds DISTRIBUTION important ever, the form of energy that humans and animals to the aerobic system are found within specialized directly rely upon for survival is chemical energy. organelles known as mitochondria. As a result, mito- nn The macronutrients—carbohydrates, fats, and pro- chondria are sometimes referred to as the “aerobic © Jones & Bartlettteins—are Learning, also known LLC as the energy nutrients. The© Jones &powerhouses” Bartlett Learning, of cells. LLC n NOT FOR SALEenergy OR trapped DISTRIBUTION in the bonds of macronutrientsNOT FORn CarbohydratesSALE OR DISTRIBUTION can be metabolized for energy both is used to make a high-energy compound known aerobically and anaerobically. In fact, carbohydrates as adenosine triphosphate (ATP). ATP is the body’s are the only macronutrient that can be metabolized direct source of energy for all biological work. The for energy via the anaerobic system. Fats and pro- role of the cellular metabolic factory is to release the teins can be metabolized only via the aerobic sys- chemical energy ©stored Jones in the& Bartlettmacronutrients Learning, and LLC tem. This is just one© reason Jones why & carbohydratesBartlett Learning, are LLC use it to make ATP.NOT FOR SALE OR DISTRIBUTIONso important to athletes.NOT FOR SALE OR DISTRIBUTION nn Energy metabolism or bioenergetics is the study of nn The aerobic energy system is composed of five met- how energy is captured, transferred, and/or utilized abolic pathways, three of which are unique to each within biological systems. The three energy systems energy nutrient. Carbohydrates are metabolized via responsible for production of ATP are the phosphagen, glycolysis, then the citric acid cycle, followed by the anaerobic,© Jones and & aerobicBartlett systems. Learning, Each of LLC these systems electron© Jones transport & Bartlett chain. Fats Learning, must go through LLC beta- hasNOT unique FOR characteristics, SALE OR DISTRIBUTIONbut they work together to oxidation,NOT FORthen theSALE citric OR acid DISTRIBUTION cycle, and finally the supply the specific ATP needs of the athlete. electron transport chain. Proteins, which are not nn The three energy systems are constantly working usually a major energy source, are first deaminated together to maintain the small ATP pools that exist and then metabolized via the citric acid cycle and in cells. Anywhere along the energy continuum, the electron transport chain. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Study Questions 1. What are the various anatomical components of the 8. What is energy? What are the various forms of digestive system? energy? Which form is most important to human 2. What are some of the similarities in the digestive physiology? processing of carbohydrates,© Jones &fats, Bartlett and proteins? Learning, How LLC9. What are the macron©utrients? Jones What & Bartlett role do they Learning, play LLC does digestion differNOT among FOR them? SALE OR DISTRIBUTIONwith regard to supplyingNOT the FOR body SALE with energy? OR DISTRIBUTION 3. What are the four processes of cellular absorption? 10. What are the three energy systems? What are their 4. Digestion breaks the macronutrients into their con- characteristics with regard to rate of production and stituent parts so that they can be absorbed. What are capacity to make energy? the constituent parts of each macronutrient? 11. What cellular organelle is called the “aerobic power- 5. What© Jones is the & differenceBartlett Learning,between a micelleLLC and a house”© Jones of the cell? & Bartlett Explain why. Learning, LLC chylomicron?NOT FOR SALE OR DISTRIBUTION 12. An eliteNOT marathoner FOR SALE is at OR mile DISTRIBUTION 17 in the race and bio- 6. What are the possible fates of the sugars, fats, and energetically in steady state. What energy systems amino acids released into the bloodstream during the are contributing to the athlete’s energy needs? Which digestion of foods? energy system is the major contributor? 7. How do cells make proteins? Where are the instruc- 13. What energy system is the major contributor of ATP © Jones & Bartletttions for proteinLearning, synthesis LLC found, and what processes© Jones &during Bartlett a discus Learning, throw? LLC NOT FOR SALEare involved OR DISTRIBUTION in making proteins? NOT FOR SALE OR DISTRIBUTION

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© Jones14. An& Bartlett athlete is Learning, running an LLC800-meter race in a track © Jones16. Which & Bartlett energy sy Learning,stem is also LLC called the “immediate meet. What energy systems are contributing to the energy system”? What high-energy compounds make NOT FORathlete’s SALE energyOR DISTRIBUTION needs? Which energy system is the NOT FORup this SALE system? OR DISTRIBUTION major contributor of ATP? 17. Which compounds are known as hydrogen carriers 15. What metabolic pathways are required to aero- and play a big role in transferring hydrogen ions to bically metabolize fats? Can fats be metabolized the electron transport chain? anaerobically? © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION References 1. Jones PJH. Lipids, sterols, and their metabolites. In: 7. Casey A, Constantin-Teodosiu D, Howell S, Hultman Shils ME, Olson JA, Shike M, Ross AC, eds. Modern E, Greenhaff PL. Creatine ingestion favorably affects Nutrition© Jones in Health & andBartlett Disease Learning,. 9th ed. Philadelphia, LLC performance© Jones and muscle & Bartlett metabolism Learning, during LLC maxi- PA: LippincottNOT FOR Williams SALE and OR Wilkins; DISTRIBUTION 1999:67–94. mal exerciseNOT in FOR humans. SALE Am OR J Physiol DISTRIBUTION. 1996;271(1 Pt 2. Guyton A. Textbook of Medical Physiology. 9th ed. Phila- 1):E31–E37. delphia, PA: WB Saunders; 1996. 8. Bizeau ME, Willis WT, Hazel JR. Differential responses 3. Brooks GA, Fahey TD, Baldwin KM. Exercise Physiology: to endurance training in subsarcolemmal and Human Bioenergetics and Its Applications. 4th ed. Boston, intermyo-fibrillar mitochrondria. J Appl. Physiol. © Jones &MA: Bartlett McGraw-Hill; Learning, 2005:31–42. LLC © Jones1988;85(4):1279–1284. & Bartlett Learning, LLC NOT FOR4. McArdle SALE WDOR, KatchDISTRIBUTION FI, Katch VL. Exercise Physiology: NOT9. FORWhite SALE TP, Brooks OR DISTRIBUTIONGA. [U-14C] glucose, alanine, and Nutrition, Energy, and Human Performance. 7th ed. Philadel- leucine oxidation in rats at rest and two intensities phia, PA: Lippincott Williams and Wilkins; 2001:134–161. of running. Am J Physiol. 1981;240:E155–E165. 5. Harris RC, Soderlund K, Hultman E. Elevation of 10. Paul GL, Gautsch TA, Layman DK. Amino acid and creatine in resting and exercised muscle of nor- protein metabolism during exercise and recovery. mal subjects by creatine© Jones supplementation. & Bartlett Clin Learning, Sci. LLCIn: Wolinsky I, ed. Nutrition© Jonesin Exercise & and Bartlett Sport. Boca Learning, LLC 1992;83(3):367–374. NOT FOR SALE OR DISTRIBUTIONRaton, FL: CRC Press; 1998.NOT FOR SALE OR DISTRIBUTION 6. Earnest CP, Beckham S, Whyte BO, Almada AL. Effect of acute creatine ingestion on anaerobic performance. Med Sci Sports Exerc. 1998;30(suppl):141. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

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