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Q What is that gut feeling inside you? A lot is going on in your stomach when you eat. For instance, epithelial cells, shown in this close-up, secrete four types of substances: stomach acid; a protective mucus that keeps the stomach from digesting itself; enzymes that break down many types of food; and hormones that control the process.

R E a d IN G T o o l b o x This reading tool can help you learn the material in the following pages.

USING LANGUAGE Your Turn Classification Organizing things into groups will show 1. Pizza, hamburger, and salad are members of the class their relationships to each other and to other things. food. List three additional members that could belong Grouping is called classification, and another word for in this class. group is class. For example, a hammer is a tool. A hammer 2. The class nutrient includes the members vitamin, is not the only type of tool. Saws, drills, and screwdrivers mineral, carbohydrate, protein, and lipid. Think of are also tools. Tool is the class and saw, drill, screwdriver, another class to which the members carbohydrate, and hammer are members of that class. protein, and lipid could belong.

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©Comstock Production Department/Alamy Images F Zinc Sodium Potassium Pho Magnesium Iodine Ir Calcium M IGURE on listed in cells and to build or repair tissues. Some of more the common minerals are stasis. amountsSmall of minerals and vitamins are to maintain needed also homeo- Minerals to people’sbeneficial than health are saturated fats. such or as cod salmon. In general, unsaturated fats are considered more ture and are found inplant oils, such as corn or olive oils, and insome fish, found inanimal products. Most unsaturated fats are liquid at room tempera- fattytheir acid chains. Saturated fats are solidat room temperature and are asclassified either saturated or unsaturated, depending on structure the of must obtain of all essential the fatty acids from you foods the eat. Fats are hooked to glycerol Your molecules. can make body some fatty acids, but you for neurons, and hormones. certain Fats consist of long chains of fatty acids Fats provide and energy key components membranes, incell myelin sheaths Fats Proteins, such shown as those in P eating avariety of plant or foods by combining plant and animal foods. minerals insweat, urine, and other waste products. You can replace by them sium help to maintain body’s the homeostasis. fluid You are constantly losing formation, muscle contraction, transmission. and nerve and Sodium potas- need. For example, red beans and together rice contain 20amino all acids. must eat combinations certain of to foods obtain amino the all acids they one essential amino acid. People do not who eat products, meat, or dairy eggs containeggs eight all essential amino acids. Most plant proteins lack at least acids, must come from you foods the eat. Foods such as meat, cheese, and amino acids it to needs build proteins. essential The amino other 8,called composed of chains of amino acids. Your can make body only 12of 20 the enzymes and many hormones that are for vital metabolism. cell Proteins are growth and repair of body’s the cells and tissues. Proteins make up also all in roteins sphorus e rals Minerals 1.3 F IGURE

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Vitamins Vitamins are organic molecules that work with enzymes to regulate cell functions, growth, and development. As shown in FIGURE 1.4, these nutrients are divided into fat-soluble vitamins and water-soluble vitamins. Fat-soluble vitamins dissolve in fatty acids. The fat-soluble vitamins A, D, E, and K can be stored in the body’s fatty tissues for future use. For this reason, taking high doses of these vitamins can actually create harmful, or toxic, levels in the body. Water-soluble vitamins dissolve in water. The water-soluble vitamin C and the B vitamins cannot be stored and are excreted in urine and feces. As a result, you need to eat foods rich in these nutrients to keep replenishing them. The National Academy of Sciences publishes recommended daily amounts of minerals and vitamins based on your age, gender, and level of activity. Apply Would a diet higher in protein or in complex carbohydrates give you more energy? Explain your answer. 9A

FIGURE 1.4 essential Vitamins Vitamin Sources Important for Fat-Soluble (Dissolves in Fat)

A (retinol) dark green, yellow, and orange vegetables, healthy skin, mucous membranes, vision fortified milk, fish and liver oils

D (calciferol) fortified dairy and whole grain products, bone and tooth formation, increase in calcium and egg yolks, fish and liver oils phosphorus absorption

E (tocopherol) vegetable oils, nuts, fish oils, meats, leafy prevention of cell damage green vegetables

K leafy green vegetables, egg yolks, liver; blood clotting and synthesis of clotting factors also made by intestinal bacteria Water-Soluble (Dissolves in Water)

B1 (thiamine) pork and red meats, whole grains, metabolism of carbohydrates dried beans and peas, eggs

B2 (riboflavin) dairy products, liver and organ meats, metabolism of carbohydrates and proteins, normal enriched whole grains growth in skin, lips, and mucous membranes

B3 (niacin) meats, dried peas and beans, whole grains metabolism of glucose, fats, and proteins

B6 (pyridoxine) meats, fish, peanuts, eggs, bran cereal metabolism of amino acids

B12 liver, meats, eggs, dairy products protein synthesis and red blood cell production

C (ascorbic acid) citrus fruits, berries, tomatoes, broccoli, antioxidant, maintenance of cartilage and bone, iron cabbage, potatoes, melons absorption, tissue repair, wound healing, healthy gums Pantothenic acid meats, dairy products, whole grains metabolism of glucose, fats, and proteins

Folic acid leafy green vegetables, liver, nuts, oranges, amino acid synthesis and metabolism, prevention of broccoli, peas, fortified cereals neural tube defects in fetuses

Biotin egg yolks, liver, soybeans metabolism of carbohydrates, proteins, and fats

Choline egg yolks, liver, whole grains production of phospholipids and neurotransmitters

930 Unit 9: Human Biology DO NOT EDIT--Changes must be made through “File info” CorrectionKey=A

MAIN IDEA Meeting nutritional needs supports good health.

A balanced diet is important throughout your life, but particularly during CONNECT TO pre-teen and early teen years. During these years, you are growing and Cellular Respiration developing faster than at any other time since the first two years of your life. You read in Cells and Energy Your bone mass is increasing nearly 40 percent, you are gaining most of your about the different ways that adult body mass, and you are developing sexual characteristics. plant and animal cells obtain To fuel this growth spurt, your body requires considerably more nutrients energy. In nearly all plant and animal cells, mitochondria use and more energy in the form of Calories consumed, as shown in Figure 1.5. A molecules broken down by calorie, with a small c, is the amount of energy required to raise one gram of digestion to build ATP, the main water one degree Celsius. One Calorie (capital C) from food equals one power source for cells. kilocalorie, or 1000 calories. One gram of protein or carbohydrate yields four Calories, while one gram of fat yields nine Calories. Calories are not the whole story, however. The rapid changes in Figure 1.6 Your food choices your body require adequate amounts of all six nutrients. Dietary experts can help you consume high-quality recommend that most of your Calories come from eating whole grains, energy and nutrients at a time fruits, and vegetables, like those shown in Figure 1.6, which are rich in fiber, when your body needs them the most. vitamins, and minerals. Also, experts suggest drinking more low-fat milk or soy drinks and water, and fewer high-sugar soft drinks and juices. High-sugar foods provide Calories but little nutritional value. Dietary recommendations include eating more lean meats and fish, while cutting down on foods high in saturated fat. It is also important to find a balance between food and physical activity so that you use about as many Calories as you consume. The U.S. Department of Agriculture (USDA) website provides information on how to develop a balanced diet.

FIGURE 1.5 Growth and Energy Needs During rapid growth, the body requires significantly more energy.

males Females 10 4000 10 4000 10 4000 10 4000 Height gain 3500 Height gain 3500 Height gain 3500 Height gain 3500 8 (cm/year) 8 (cm/year) 8 (cm/year) 8 (cm/year) Required 3000 Required 3000 Required 3000 Required 3000 Calories/day Calories/day Calories/day Calories/day 6 2500 6 2500 6 2500 6 2500 2000 2000 2000 2000 4 1500 4 1500 4 1500 4 1500 1000 1000 1000 1000 2 2 2 2 Height gain (cm/year) Height gain (cm/year) Height gain (cm/year) Height gain (cm/year) Height gain 500 Calories/day Required 500 Calories/day Required 500 Calories/day Required 500 Calories/day Required 0 0 0 0 0 0 0 0 8 9 10 11 1312 14 15 171618 8 9 10 11 1312 14 15 171618 8 9 10 11 1312 14 15 171618 8 9 10 11 1312 14 15 171618 Age (years) Age (years) Age (years) Age (years)

Sources: Adapted from JM Tanner: Growth at Adolescence, ed.2, Oxford; Food and Nutri- Contrast What differences do you tion Board: Recommended Dietary Allowances, ed. 10, National Academy Press; Institute notice between the two charts? of Medicine, Food and Nutrition Board, Dietary Reference, National Academies Press. ©David Young-Wolff/PhotoEdit ©David

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Figure 1.7 Reading a Food Label The information on a food label, such as the one in Figure 1.7, can help you make good choices and Macaroni and Cheese compare the values of different foods. The label shown here is from a box of macaroni and cheese.

1 Know serving size. 1 Serving size and number This measurement varies from one product to another. In this case, 2 Check Calories and one serving equals one cup. Notice that this Calories from fat per serving. container holds two servings. 2 Calories and Calories from fat The numbers 3 Limit these listed on the label are for one serving only. If nutrients. you eat both servings, you are actually getting 500 Calories, nearly half from fat. 4 Get enough of these nutrients. 3 Nutrients to limit Americans usually consume too much saturated fat, trans fat, cholesterol, and sodium. Trans fat is a type of fat that can cause cell damage. A diet high in these nutrients is linked to obesity, which affects more and more Americans of all ages. Footnote explains Too much sodium can raise blood pressure by % Daily Values causing the body to retain water. 4 Nutrients to target Americans need to consume enough of these nutrients each day. Notice

Source: U.S. Food and Drug Administration that this product is low in vitamins and minerals, except for calcium, and has no dietary fiber. The wheat used in the macaroni has been processed until there is no fiber left. Web As information on the label suggests, if you eat this product, you will also HMDScience.com need to eat whole grains, vegetables, and fruits during the day to obtain the

GO ONLINE nutrients that are missing from this food. Obesity Analyze What nutritional advantages do unprocessed foods offer over processed foods?

Self-check Online HMDScience.com 32.1 Formative Assessment GO ONLINE Reviewing Main Ideas Critical thinking CONNECT TO 1. What six types of nutrients must you 3. Apply Explain why vegans—people Cellular Respiration consume to stay healthy? Give two who eat no animal products—must 5. All cells need ATP to power examples of how nutrients help to take care to include all the essential their metabolic processes. maintain homeostasis. 9A amino acids in their diet. Explain why eating carbohy- 2. What information besides the 4. Contrast How do the functions of drates is so important to the number of Calories can help you vitamins and minerals differ from process of cellular respiration. make good food choices? the functions of proteins and carbohydrates? 9A

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32.2 Digestive System

9C, 10A, 10C key concept the digestive system breaks down food into simpler molecules. VOCABULARY MAIN IDEAS digestion Several digestive organs work together to break down food. digestive system Digestion begins in the mouth and continues in the stomach. sphincter Digestion is completed in part of the small intestine. esophagus peristalsis stomach Connect to Your World chyme What would you do to help advance scientific understanding? In June 1822, Alexis St. small intestine Martin was shot in the stomach and treated by William Beaumont, an Army surgeon. bile The 19-year-old St. Martin recovered, but the bullet wound left a small hole in his stomach. Beaumont covered the hole and persuaded St. Martin to let him observe 9C identify and investigate the digestive process by tying foods to a string, dropping them into the stomach the role of enzymes; 10A describe hole, and retrieving them at different times to see how quickly different foods were the interactions that occur among systems that perform the functions digested. Over ten years, the experiments yielded a wealth of information about the of regulation, nutrient absorption, reproduction, and defense from digestive process. St. Martin married, had children, and lived to the age of 76. injury or illness in animals; 10C analyze the levels of organization in biological systems and relate the levels to each other and to the MAIN IDEA 9C, 10A, 10C whole system Several digestive organs work together to break down food. Digestion is the process by which the large complex molecules in food are broken down into smaller molecules that can be used by the body. The digestive system is a collection of organs that breaks down food into energy that can be used in cells. It is like a factory that takes things apart instead of putting them together. The major organs of this “disassembly line” include the mouth mouth, esophagus, stomach, pancreas, liver, gallbladder, large and small esophagus intestines, rectum, and anus, as shown in Figure 2.1. Rings of muscle, called liver sphincters (SFIHNGK-tuhrs), separate one section from another. The open- ing and closing of these sphincters and the contractions of smooth muscle in stomach the walls of the organs keep food moving in one direction. gallbladder Digestion takes place through the interactions of enzymes, stomach acid, pancreas hormones, bile from the liver, and a network of nerves and muscles through- large out the digestive system. Each organ contributes to breaking food down. For intestine instance, in the mouth, salivary glands secrete an enzyme that helps to digest small starches. The stomach releases enzymes that break down proteins. intestine Once digestion is complete, nutrients are absorbed by the body and trans- rectum/anus ported by the circulatory system and lymphatic system to all the cells. Finally, undigested materials are eliminated as liquid and solid wastes. The entire Figure 2.1 The major digestive process—from food entering the mouth to wastes leaving the body—takes organs are separated by sphincters, about 24 to 33 hours per meal. which help keep food moving in one direction. Predict What might happen if the digestive sections were not divided by sphincters?

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MAIN IDEA 9C Digestion begins in the mouth and continues in the stomach. You may have heard someone telling their children, “Chew your food—don’t just gulp it!” This is actually good advice, because the first step in breaking down food is mechanical and chemical digestion in the mouth.

esophagus Digestion in the Mouth You unwrap the sandwich you brought for lunch and bring it up to your mouth. Mechanical digestion begins the moment you bite into the sandwich and start chewing. Your teeth shred and grind the food into smaller pieces. muscles Your tongue keeps the pieces positioned between your teeth. Chemical contract digestion, on the other hand, involves the action of enzymes. As you chew your food, the salivary glands release saliva that moistens the food and muscles relax contains an enzyme called amylase (AM-uh-lays). Amylase begins the breakdown of complex starch molecules into sugars. Once food has been chewed and mixed with saliva, the tongue pushes it to food the back of the mouth. As you swallow, the food moves into the esophagus (ih-SAHF-uh-guhs), a tube that connects the mouth to the stomach. Food is kept moving down the esophagus by the action of peristalsis, as FIGURE 2.2 shows. Peristalsis (pehr-ih-STAWL-sihs) is the rhythmic, involuntary stomach contraction of the smooth muscles in the walls of digestive organs. Digestion in the Stomach The next stop for your thoroughly chewed sandwich is the stomach. The stomach is a muscular sac that can stretch to nearly twice its original size and Figure 2.2 As food enters the holds up to 2 liters (2 qt) of food. The stomach continues the digestion that esophagus, muscles behind the food contract, pushing it forward, began in the mouth. Proteins are digested in the stomach and small intestine, while the muscles in front of the but fats and sugars are digested only in the small intestine. Major enzymes food relax. This rhythmic squeez- and their functions in the digestive system are listed in FIGURE 2.3. ing, called peristalsis, keeps food moving in one direction. The walls of the stomach contain three layers of smooth muscle that contract about every 20 seconds. This churning action breaks food into even smaller pieces and mixes the food with the stomach’s digestive juices.

FIGURE 2.3 Major Digestive Enzymes Enzyme Digestive organ Function Salivary amylase mouth breaks down starches into simpler sugars Pepsin stomach breaks down proteins

Maltase, lactase, sucrase small intestine breaks down sugars into simpler molecules

Peptidase breaks down proteins into amino acids

Trypsin small intestine, pancreas continues breakdown of proteins

Amylase continues breakdown of starches

Lipase aids in breaking down fats

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As FIGURE 2.4 summarizes, chemical digestion occurs along with the CONNECT TO churning of mechanical digestion. The stomach lining secretes gastric juice Chemistry containing hydrochloric acid (HCl) and the digestive enzyme pepsin. Gastric Hydrochloric acid (HCl) is so juice is acidic enough to kill most bacteria found on food and to break the strong that it can dissolve an iron bonds between protein molecules. Pepsin also breaks some chemical bonds nail in a matter of hours. To between the amino acids in proteins. Digestive juices and enzymes turn your protect your stomach lining, specialized epithelial cells secrete partly digested sandwich into a semi-liquid mixture called chyme (kym). bicarbonate, a base substance. The stomach empties as peristaltic actions push the chyme against the Bicarbonate neutralizes the acid to keep it from burning through sphincter that separates the stomach from the small intestine. With each your stomach lining. contraction, the sphincter opens slightly, and chyme squirts into the small intestine, where digestion continues. It takes from two to six hours to empty the stomach after a meal. Once the stomach is empty, the production of gastric juice stops. What keeps the stomach from digesting itself? First, pepsin is active only when there is food to digest. Second, the stomach secretes a layer of mucus to protect itself from its own acidic environment. Even so, cells in the stomach lining are replaced every few days to maintain the protective layer of mucus. Apply If you ate a meal of spaghetti and meatballs, where would chemical digestion of the pasta and meat begin?

FIGURE 2.4 Mechanical and Chemical Digestion The digestive organs use mechanical and chemical digestion to break food down into simple molecules.

Mouth Mechanical Chemical Chewing shreds and Salivary amylase grinds food into breaks down starches smaller particles. into simple sugars.

stomach Mechanical Chemical Smooth muscle contrac- HCl and pepsin break tions churn food to break down proteins. it down and mix it with digestive juices.

small intestine Mechanical Chemical Muscular contractions Enzymes, bile, and break down and mix food hormones finish with digestive enzymes, digestion of proteins, bile, and hormones. sugars, and fats.

CRITICAL Do you think a high-carbohydrate or a high-protein VIEWING meal would be digested more quickly? Explain.

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MAIN IDEA 9C Digestion is completed in part of the small intestine. The remaining carbohydrates, proteins, and fats from your sandwich are Figure 2.5 The liver and digested in the duodenum (doo-uh-DEE-nuhm), the section of small pancreas help digest fats, carbo- intestine closest to the stomach. The small intestine is a long, narrow tube hydrates, and proteins in the small in which most digestion takes place. Smooth muscle contractions churn the intestine. The liver secretes bile through the gallbladder, and the food, and chemical digestion further breaks down the complex molecules. pancreas secretes an alkaline fluid As shown in FIGURE 2.5, enzymes and hormones from the pancreas, liver, and and digestive enzymes. gallbladder flow through ducts into the duodenum to help complete the digestive process. liver The pancreas is a small gland located behind the stomach. When chyme first enters the small intestine, the pancreas releases an alkaline bile stomach fluid to help neutralize the acid and stop the action of pepsin. The chyme pancreas also releases enzymes to break down starches further into bile simple sugars. For example, lactase is an intestinal enzyme that breaks enzymes down lactose, a sugar found in milk. The pancreas also produces an pancreas enzyme called lipase that splits fat into fatty acids and smaller molecules. gallbladder The liver, which filters blood, is also a digestive organ. It produces a chemical substance called bile that helps to digest fats. Bile is stored in duodenum a smaller organ, the gallbladder. When bile is needed to digest fats, it is released through ducts that empty into the duodenum. The bile breaks down large globules of fat into smaller droplets for further digestion. Proteins entering the small intestine have already been broken down by the action of pepsin and gastric juice into smaller chains of amino acids. In the duodenum, enzymes finish the process by breaking these chains into individual amino acids. By the time chyme has passed through the duodenum, food has been broken down into small molecules. Section 3 describes how these molecules are absorbed by the body. Apply How would the pancreas and liver help to digest ice cream?

Self-check Online HMDScience.com 32.2 Formative Assessment GO ONLINE Reviewing Main Ideas Critical thinking CONNECT TO 1. What is the main function of the 4. Infer Some people cannot consume Cell Structure digestive system? dairy products, such as milk, without 6. The cells of the stomach 2. Give an example of mechanical and their stomach becoming upset. lining produce a great deal of chemical digestion in the mouth and Explain. mucus. If you were to view in the stomach. 9C 5. Predict If a person has his or her such a cell under a micro- gallbladder removed, what changes in scope, what type of organ- 3. What organs help to continue diet should be made? Why? elle would you expect digestion in the small intestine? to see in abundance?

936 Unit 9: Human Biology DO NOT EDIT--Changes must be made through “File info” CorrectionKey=A G Online!

Eating and Excreting

Web BIOLOGY BIOLOGY Run the Digestive System Obesity Kidney Structure The Move a snack from the Obesity is on the rise, but is the nephron is the functional mouth through the large answer as simple as “eat less and unit of the kidney. Explore intestine and get as much exercise more”? Examine the causes how blood is filtered as it nourishment out of the and health risks of obesity, and learn passes through the long and food as possible. how people can take control of their winding renal tubes of the weight. nephron. ©Getty Images Royalty Free

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Specialized Structures for Absorption As you look over the diagram in FIGURE 3.1, notice that the lining of the small R E A D I N G TO OLB ox intestine is ridged and folded. These structures increase the surface area and TAKING NOTES slow the passage of material through the intestine. Slower motion allows more Use a main idea and supporting time for nutrients to be absorbed. The folds of the lining are covered with detail diagram to help you villi. Villi (VIHL-eye) are small fingerlike projections, covered with epithelial remember the facts about cells, that absorb nutrients. absorption.

In turn, every epithelial cell on the villi has thousands of tiny projections absorption occurs in called microvilli that add even more surface area to absorb nutrients. Each small intestine microvillus is smaller than the period at the end of this sentence. The photo- folds, villi, microvilli graph in the diagram shows microvilli covering the epithelial cells like a increase surface dense carpet. area, absorption Absorption of Different Nutrients As digestion is completed, nutrients are absorbed in each of the three parts of the small intestine: the duodenum, the jejunum, and the ileum. Together, these parts measure about 6 meters (about 20 ft) long. Villi in each of the three sections absorb different nutrients. Duodenum Most simple sugars, amino acids, and minerals such as calcium CONNECT TO and iron are absorbed by villi in the duodenum. These nutrients diffuse into the circulatory system and are carried to the liver. Cell Structure As you read in Cell Structure Jejunum The villi in the jejunum (juh-JOO-nuhm) absorb glucose along with and Function, plant cell walls some amino acids, vitamin C, most B vitamins, and some water. These nutri- are made of cellulose, or fiber. These tough cell walls cannot ents diffuse into the circulatory system to be distributed throughout the body. be broken down or absorbed Ileum The villi in the ileum (IHL-ee-uhm) absorb fat-soluble vitamins and in the small intestine. Instead, fiber moves through the small vitamin B12, fatty acids, cholesterol, and some water. The nutrients empty into intestine to the large intestine. lymph and blood vessels and are distributed to the cells.

QU I CK L AB Modeling 3E Villi in the Small Intestine In this lab, you will design a model of the villi in the lining of the small intestine. Materials • 4 large paper cups Problem How can you model the function of villi in the small intestine? • water • 8 paper towels Procedure • timer 1. Use a paper cup, water, and paper towel to make a model of the villi in the lining of the small intestine. 2. Make three new models that are different. To do this, change one material to determine which model most effectively shows the action of the villi. 3. Determine which of your models most effectively models the villi. Analyze and conclude 1. Summarize Explain how this experiment models the action of the villi in the small intestine. 2. Apply Write a definition to describe how you measured each model’s effectiveness. 3. Analyze Which model was most effective? How do you know?

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32.4 Excretory System

10A, 10C key concept the excretory system removes wastes and helps maintain homeostasis. VOCABULARY MAIN IDEAS excretory system The excretory system eliminates nonsolid wastes from the body. kidney The kidneys help to maintain homeostasis by filtering the blood. ureter Nephrons clean the blood and produce urine. urinary bladder Injury and disease can damage kidney functions. nephron glomerulus dialysis Connect to Your World In 1943, Dutch physician Willem Kolff, who treated kidney patients, constructed the 10A describe the first machine to filter the blood of patients whose kidneys had temporarily stopped interactions that occur among functioning. Kolff circulated their blood through synthetic sausage skins submerged systems that perform the functions of regulation, nutrient absorption, in a saltwater bath. The high concentration of salt in the water drew metabolic reproduction, and defense from wastes out of the blood through tiny pores in the synthetic skins. The filtered blood injury or illness in animals and 10C analyze the levels of was then returned to the patients. However, Kolff’s machine worked well only for organization in biological systems people with temporary kidney failure. Today, modern kidney machines can help and relate the levels to each other and to the whole system people even when their kidneys have permanently failed.

Main Idea 10C The excretory system eliminates nonsolid wastes from the body. If the digestive system is like a disassembly and distribution line, the excretory system is a like a group of waste treatment and disposal facilities. The skin excretory system is the body system that eliminates nonsolid wastes through lungs sweat, urine, and exhalation to help maintain homeostasis in the body. The

waste products include toxic materials, excess water, salts, CO2, urea, minerals, and vitamins. The main organs of this system are the skin, lungs, kidneys, ureters, urinary bladder, and urethra, as shown in FIGURE 4.1.

The lungs remove excess CO2 and some water vapor through exhalation.

kidneys This action maintains the balance of O2 and CO2 in your blood. Sweat glands in the skin release excess water and salts. Sweat not only removes wastes but also cools the body to maintain a stable internal temperature. ureters The kidneys are organs that eliminate wastes by filtering and cleaning the blood to produce urine. The urine moves through the ureter, the bladder, and urinary bladder the urethra. The ureter (yu-REE-tuhr) is a tube that carries urine from each urethra kidney to the bladder. The urinary bladder is a saclike organ that can store up to half a liter (over 2 cups) of urine at one time. The urine is released through Figure 4.1 The excretory a single tube, the urethra, into the outside environment. system not only excretes nonsolid wastes but also maintains Connect When you are exercising, what organs of the excretory system are the body’s homeostasis. eliminating wastes? 10C

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MAIN IDEA 10A The kidneys help to maintain homeostasis by filtering the blood. The kidneys are among the main organs responsible for maintaining fluid and chemical balances in your body within the limits that support life. One quarter of your blood supply passes through your kidneys every minute. Once the blood is filtered, cleaned, and chemically balanced by the kidneys, it is returned to the circulatory system. Structure of the Kidneys cortex Your kidneys are a pair of bean-shaped organs, each about the size of your fist. They are located on the right and left sides of the lower back. Each kidney weighs about as much as a baseball. medulla Most people are born with two kidneys. However, if one is damaged or must be removed, you can still live comfortably renal with only one kidney. artery The main parts of the kidney are illustrated in FIGURE 4.2. Each kidney has an inner layer, called the medulla, and an outer layer, called the cortex. The cortex is packed with nephrons, which extend through the cortex and partly into the medulla. A nephron (NEHF-rahn) is renal the individual filtering unit of the kidney. Each of your vein kidneys contains about 1 million nephrons. A large volume of blood continually enters the kidneys ureter through the renal artery and exits through the renal vein. The (to bladder) word renal means “relating to the kidneys.” The function of the kidneys is largely controlled by how much water and how many salts and other materials are concentrated in the blood. Hormones released in response to these concentrations help to regulate kidney function. Figure 4.2 The bean-shaped kidneys are the main blood Kidneys and Homeostasis filtration and chemical balancing The kidneys have three basic functions in maintaining homeostasis. organs in the body. The cortex • They remove waste products from the blood, such as those produced from and medulla layers contain over 1 million nephrons, which are the digestion and cell respiration. kidneys’ main filtering units. • They help to maintain electrolyte, pH, and fluid balances in the body. • They release hormones that help to keep bones healthy, to produce red blood cells, and to regulate blood pressure. What if the kidneys fail to work properly? Waste products quickly build up in the blood, causing serious disruptions in homeostasis in many organ systems. For example, imbalances in electrolytes such as sodium and potassium could disrupt the rhythm of the heart, causing the organ to fail. A buildup of toxic substances such as ammonium salts in the blood can impair the functioning of neurons in the brain. Someone with this condition would quickly become confused and disoriented. Infer What might be one reason why so many nephrons are needed in the kidneys?

Chapter 32: Digestive and Excretory Systems 943 CorrectionKey=B DO NOT EDIT--Changes mustbemadethrough “File info” 944

through capillary walls. the glomerulus, molecules diffuse to areas oflower concentration. In from areas of higherconcentration into andoutofcell membranes Function You read inCell Structure and C published in1873. book onhumananatomy, He identifiedtheloop inhis physician FriedrichG.J.Henle. named after theGerman structure inthenephron, was identified thisstructure in1831. surgeon andanatomist who William Bowman, aBritish capsule was namedafter Sir identified them.Bowman’s after thescientists whofirst At times,structures are named VOCABULARY ell Unit 9:HumanBiolog CO The READI NN M loop ofHenl that materials diffuse embra EC N T

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arteriole, avenule, of and capillaries atangledball that is known as the proteins, and platelets—stays blood. inthe Anything large too to move out of capillaries—such the cells, plasma as blood capsule. Urea is awaste product produced by breakdown the of proteins. of capillaries the and into Bowman’s electrolytes, and urea are pushed out as water, amino acids, salts, glucose, under pressure, such molecules small each nephron. is blood the Because movesthen into glomerulus the of itneys, flows into arterioles the and capsule. cup-shaped Bowman’s structure called glomerulusEach is tucked into a removed one to time reduce final volume the of urine. and is concentrated loop inthe of Henle. The loop of Henle is where water is pH ofwithin normal blood the limits. Filtrate moves out of Bowman’s capsule Removal of some of ions these helps to maintain homeostasis by keeping the filtrate.in the materials These include ions such as potassium and hydrogen. Urine is made up of water, urea, excess salts, and other materials that remain Finally, waste the products that are not reabsorbed are excreted urine. inthe Excretion Materials of and (Na sodium Thisblood. process ensures that nutrients such as water, amino acids, glucose, percent is excreted as urine. What happens to other the 99percent? process about 180liters of day, (47.6gal) filtrate every yet only about 1 The materials inBowman’s capsule are filtrate. the called The nephrons Materials of Reabsorption glomerulus As shown in Filtration to Finally, blood. the remaining the waste products are excreted urine. inthe into nephron. the Next, some of materials these are reabsorbed and returned and excretion. First, water and other materials move out of capillaries the and The nephrons inathree-step clean blood the process: filtration, reabsorption, and Na and produce less urine. urine. If you little too drink water, nephrons the reabsorb will more and fluid much water, nephrons the reabsorb will less of and fluid the produce more ephrons clean bloodproduce urine. the and ephrons M ai When Mos n I + t of filtrate the is reabsorbed into capillaries the and returns to the de helps to maintain your balance. fluid For example, ifyou too drink the blood enters blood the kid the a (gloh-MEHR-yuh-luhs). FIGURE 4.3, + ) are made available to body. the The reabsorption of water each nephron is supplied through with blood an - VISUAL VOCAB Glomerulus, Latin glomus, whichmeans “ball.” capillaries, isaword based onthe colored SEM;magnification 700 atangled ball of 3

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FIGURE 4.3 Structures and Functions of the Nephron Biology HMDScience.com The nephron filters the blood and produces urine through a three-step process. GO ONLINE Kidney Structure 1 glomerulus Filtration Water, electrolytes, amino acids, glucose, urea, and other small molecules diffuse out of the blood, creating the filtrate.

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3 Excretion In the loop of Henle, water can be reabsorbed one final time to reduce the volume of urine. The remaining urine flows into a collecting duct that leads to the ureter.

CRITICAL What might be one reason that the rest of the nephron VIEWING is so long compared with the glomerulus?

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plants possible. children made theorgan trans- matches between mother and José Alvarez. Theclose tissue ofaliverand part from herson, her daughter, Proscia, Rosario (center) received akidney from F igure Unit 9:HumanBiolog 4.4

Maria Alvarez y Injury and diseaseInjury can damage kidney functions. ca Apply

containing about 95percent water and 5percent waste products. urgethe to urinate. In ahealthy person,is urine aclear, pale-yellow fluid of walls inthe bladder the to signals brain, send the nerves full, and you get about 1liter (16oz) of before urine it must emptied. be When bladder the is kidney failurekidney are transplant akidney or of use the dialysis. and nephrons the ability their lose to The filter blood. only the treatments for morethem porous. As aresult, many too substances pass through walls, the pressureblood can damage glomerulus inthe walls and capillary the make damage to nephrons. The presence of much too or blood inthe high glucose by an infection, diabetes pressure and blood high are more often causes the of any Although function. kidney your damaged can kidneys be inan accident or You can live comfortably with one healthy kidney, but you cannot live without and, ifso, of that types the drugs may involved. be urine. test Aurine is one way to determine aperson is whether abusing drugs, aretaken broken down liver, inthe filtered by and kidneys, the excreted in the largetoo through glomerulus. the to diffuse Also, any that drugs aperson has have damaged been by an infection or injury. Ordinarily, substances these are thaturine contains sugar, protein, or may blood indicate that nephrons the contenturine but for also materials that should not there. be For example, sample of as part aroutine examination. The doctor is checking for normal When you go for aphysical checkup, doctor the may ask you for aurine Urine th psule: red blood cells, cells, blood red psule: M rough ureter the and intobladder. urinary the The adult bladder can hold ai The moves then urine into ducts. From collecting the there it flows

n I Which of the following substances would you find mainly in Bowman’s in mainly you would find substances following the of Which T de esting a As described in As described K football. Any injury to one the fatal. could be kidney generally avoid heavy contact such sports, as hockey, wrestling, or or from ordinary cuts recipient and Both bruises. and donor must more be personthe will vulnerable to infections from other people organ. possibilitynew the the rejects body the means This also that immunethe system for rest the of his or her life to guard against tions, however. The recipient have will that to drugs take suppress patient the function, can live afairly normal life. from someone is who not related. to begins kidney Once new the patient’s more accept kidney new the will body easily than akidney or child. The tissues of people both are similar enough that the can receive from akidney acloserelative, such as asibling, parent, idney Bot h the recipienth the and donor the must live with some restric- T ransplant N a + , glucose, plasma proteins, water, or amino acids? water, amino or proteins, plasma , glucose, F igure 4.4, apatient transplant akidney needs who

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Kidney Dialysis FIGURE 4.5 Dialysis Process If a kidney donor is not available or the patient cannot have surgery, dialysis can The basic unit of a dialysis A trap prevents air bubbles from save the person’s life. Dialysis is a treat- machine filters wastes entering patient’s blood before it ment in which a patient’s blood is cleaned from the blood. is returned to the body. and chemically balanced through a filter and mechanical process. The blood is then bubble trap returned to the patient’s body. Clean dialysis The main unit of a dialysis machine, as fluid flows in. shown in FIGURE 4.5, acts like the glomer- roller dialysis unit ulus. Blood moves from a vein in the arm pump into the filtering unit. The tubing in the unit is porous, like the capillary walls, A pump pushes blood through which allows waste materials to diffuse into dialysis unit. Waste materials the dialysis fluid. The fluid is continually diffuse out of the replaced to carry wastes out of the unit. The blood, through membranes, and into the Used dialysis chemical makeup of the fluid is as close to dialysis fluid. fluid flows normal blood as possible. The process out. takes 3 to 5 hours and is done three times Analyze Why does the dialysis fluid need to be a week in the hospital or with a smaller continually replaced? dialysis machine in a patient’s home. A few patients may prefer not to use a dialysis machine. Instead, they may be given peritoneal (pehr-ih-tuhn-EE-uhl) dialysis, in which the lining of the patient’s abdomen acts as a blood filter. Dialysis fluid is pumped through tubing into the abdomen. Waste products and excess fluid move from the bloodstream into the dialysis solution. The waste-filled fluid is drained from the abdomen and replaced several times until the blood is cleaned and chemically balanced. Summarize Explain why people without kidney function would need to have dialysis at least three times a week.

Self-check Online HMDScience.com 32.4 Formative Assessment GO ONLINE Reviewing Main Ideas Critical thinking CONNECT TO 1. How do the main organs of the 5. Apply When kidney function is Respiration excretory system get rid of wastes? impaired, the pH level in the blood is 7. Compare the alveoli in the 2. Give two examples of how kidneys disrupted. How would this loss of lungs to the nephrons in the help to maintain homeostasis. homeostasis affect the body’s cells? kidneys. List the ways in 10A 10A, 10C which their structures and 6. Explain Briefly explain the following functions may be similar. 3. Describe the main structures of the 10C nephron and their functions. sentence: “Filtration of the blood is relatively nonselective, but reabsorp- 4. Explain how dialysis is similar to the tion of materials is selective.” way the kidneys filter the blood.

Chapter 32: Digestive and Excretory Systems 947 CorrectionKey=A DO NOT EDIT--Changes mustbemadethrough “File info” Unit 948

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CHAPTER 32 G N I D A E R

separating digestive sections.” to describe mightbe“ring sphincter ofmuscle that describes For itsmeaning. example, phrase ashort For each vocabulary term below, write phrase ashort Keep ItShort

food into asemiliquid substance called chyme.” might write, “Digestive juices inyour stomach turn example, for theterms stomach andchyme,you clearly show how theterms are connected. For For e V R 32.2 32.1 vo Chapter 10. 8. 9. 11. 6. 4. 2. 5. ocabulary Connections 3. 1. 7. eviewing

glomerulus nephron Calorie vitamin small int digestion, bile ureter absorp meaning relates to theprocess ofdialysis. meaning “to break uporto dissolve.” Explain how this The term di relates to what chyme is. esophagus, perist meaning “juic The term chymecomes from theGreek word khumos ,

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function? How doesdiabet Describe thesteps involved inthisprocess. The nephrons filter thebl homeostasis. examples ofhow thissystem helps thebodymaintain List themainorgans ofthee Explain themainpurpos drates, proteins, andfats take place? which organs doesthechemical digestion ofcarbohy- The main functions of thekidneyThe mainfunctions diet affec What are thetwo of thecolon? mainfunctions How can functions. functions. the structure ofthekidney helps itcarry outthese andchemicalfluid balances inthebody. Explain how sources ofenergy for thebody? maintain homeostasis. Whichnutrientsare themain process? in chemical digestion. List thesixtypesofnutrientsbodyneedst from thesma How are thenutrients from digested foods transported duodenum. What dig Describe how thedigestion offood iscompleted inthe ca What isthedifference between mechanical andchemi- import Explain whymeetingnutritional needsisparticularly l digestion? Give three examples ofenzymesinvolved HMDScience.com Interact ant duringpre-teen andteen years. t the functions ofthis organ?t thefunctions

32.4 M ll intestinell to thebody’s cells? A 10C

I es orhighblood pressure affect kidney dialysis glomerulus nephron urinary bladder ur kidney excretory system N i ve Review eter Chapter 32: Digestive andExcretory Systems I 10C estive organs are involved inthis DEA e ofthedigestive system. In ood andproduce urine. S 9C xcretory system. Give two s are to maintain 9A 10C o 10A

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Critical Thinking 23. Analyze A deficiency in calcium can cause spasms in the Analyzing Data Identify Outliers calf muscles at night. A woman complains to her doctor To educate young people about diet and health, a local about this problem, yet she gets plenty of calcium in her hospital offered glucose testing so teenagers could learn diet. The doctor wants to check her kidney functions. more about how their bodies were functioning. Testing Why would he suspect a problem with her kidneys? was done one to two hours after each meal so that the 24. Infer A gastric ulcer is a type of sore that appears in the food was digested and nutrients were absorbed into the stomach lining. The ulcer can be caused by infection or body. In a healthy person, glucose levels should be by overuse of products like aspirin or ibuprofen. How 80–120 mg/dL of blood before a meal and less than might a gastric ulcer affect a person’s ability to digest 180 mg/dL after food is digested. The graph below food in the stomach? shows the results for one teenager. Use the graph to answer the next two questions. 25. Infer A teenager wants to build muscle so he can compete better on the wrestling team. He decides to Glucose Levels eat a diet of mostly meat and fruit juices. Within a week, he is constipated. What probably happened, and how 200 B = Breakfast L L = Lunch can the problem be corrected? D = Dinner B L D L D B D Interpreting Visuals 150 B L D D B B L Molecules move across a membrane by means of active or passive transport. In active transport, molecules can 100 be pumped across a membrane into areas of higher or (mg/dL) levels Glucose Day 1 Day 2 Day 3 Day 4 Day 5 lower concentration. In passive transport, molecules can move only from an area of higher concentration to Testing times at meals an area of lower concentration. Use the following diagram to answer the next three questions.

membrane 29. Analyze What is the typical glucose range for this teenager after meals? Which point is the outlier in this outside nephron tubule inside nephron tubule data set?

Na+ 30. Evaluate What are some possible explanations for the + Na active outlier data? How should the scientists proceed? transport

H2O Making Connections 31. Blog a Snack-Food Challenge More companies are H O passive 2 offering alternative, “healthier” snack foods, such as transport protein bars or fruit strips. Your challenge: Use your knowledge of food labels to compare the nutritional information on these products with other snack foods 26. Analyze Look at the concentrations of Na+ ions and such as candy bars and potato chips. Write a blog entry + H2O in the diagram. Can more Na ions move out of the on your findings, including each product’s nutritional tubule? Explain your answer. content, its cost, and where you can buy it. 27. Infer The membrane can change to let more or less 32. Synthesize The photo on the chapter opener shows water through. If a person were dehydrated, how might the specialized cells in the lining of the stomach. Use the membrane change? Explain. what you know about the digestive process and the digestive tract to explain why the processes that occur 28. Evaluate If the body contains too much fluid, which in the stomach could not occur anywhere else. way would H2O molecules move across the membrane? 10C Explain your answer.

950 Unit 9: Human Biology Biology End-of-Course Exam Practice

Record your answers on a separate piece of paper. 10C MULTIPLE CHOICE 4 Chemical digestion occurs throughout the digestive tract. The stomach releases pepsin, the 2E liver and gallbladder release bile, the salivary 1 glands release amylase, and the pancreas releases an alkaline fluid. Together, these processes are an Ef fect of Diet on Weight Loss and Heart Disease example of — No Prescribed Type of Diet Diet Diet A Diet B A the release of unnecessary chemicals Weight Loss 4% 6% 5% B coordinated function within an organ system Heart disease 7% 15% 8% reduction C a positive feedback loop between organs Dropout rate 0% 50% 35% D a negative feedback loop between organs

Scientists studying the effects of two different 10A, 10C diets monitored three groups of people for one 5 Lungs are part of both the respiratory system and year. The first group was not asked to change the the excretory system. In their function as way they ate. The second group followed Diet A. excretory organs, the lungs help remove which The third group followed Diet B. The first group waste products from your body? was asked not to change their diets in the study A oxygen and water vapor because — B oxygen and carbon dioxide A scientists knew that people would drop out C carbon dioxide and water vapor B scientists knew this group would lose weight D water vapor only C the group acted as a control for the study D the group acted as a model for the study THINK THROUGH THE QUESTION Think about what is present in the air that is not 3E, 10C required by the respiratory system, and therefore 2 A student made a simple model to demonstrate would be removed by the excretory system. digestion. A plastic bag and mallet were used to represent the chewing action of teeth in the mouth. A deflated balloon that could be twisted to churn food represented the stomach. 10A, 11A Pantyhose that could be squeezed and stretched 6 Which of these terms best completes the concept were used as a small intestine. One limitation of map below? this model is that —

A it does not include chemical digestion kidneys B it does not include mechanical digestion maintain remove release C the order of the organs is incorrect D model parts are each made of the same thing balance ?? hormones of from that regulate 10A, 10C 3 In order for cells of the body to receive nutrients electrolytes pH ﬂuids blood blood pressure from the food that we eat, digestion must be followed by — A nutrients A excretion B water B fluid retention C waste products C respiration D red blood cells D absorption

Chapter 32: Digestive and Excretory Systems 951