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Home , External anal sphincter, Fauces (throat), Haustrum (anatomy), Internal anal sphincter, Taenia coli

The Digestive System Chapter 15

Food is vital for life because it is the source of energy that drives the chemical reactions occurring in every cell. Energy is needed for muscle contraction, conduction of impulses, and secretory and absorptive activities of many cells. Food, however, is not in a state suitable for immediate use as an energy source. The organs that mechanically and chemically break down food into usable molecules are collectively called the digestive system.

Contents: 1. Oral cavity

2.

3.

4.

5.

6.

Accessory glands/organs = contribute to digestion but food does not pass through.

1. Salivary glands 2. Pancreas 3. Liver 4. Gall bladder

Functions:

1. Ingestion – taking food/drink into the body

2. Digestion – mechanical and chemical breakdown of food

3. – movement of food through digestive system

4. Absorption – taking nutrients into bloodstream

5. Egestion – elimination of unwanted/ undigested foods from body

6. Sensory Reception – sense of taste (chemoreceptors)

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1. Oral Cavity = . INGESTION. Lined with stratified squamous. Function: protection from abrasion

vestibule = space between / and teeth

lips = = orbiculans oris muscle

cheeks = skeletal muscle = buccinators muscle

= boundary between oral cavity and oropharynx. Location: between posterior and tip of uvula.

A. tongue

A large, flexible muscular organ. Covered with stratified squamous. Protection from abrasion. –superior surface contains chemoreceptors (taste buds)

B. Teeth

Normally, 32 teeth in adults. Tooth socket = alveolus Each tooth held in place by periodontal ligaments

tooth formula = 2 1 2 3 2 1 2 3

2 2. Accessory Glands of the Oral Cavity - 3 pairs of salivary glands located external to oral cavity - each has a duct that carries saliva into mouth (exocrine gland) -ducted! - functions: 1) keep mouth moist 2) begin chemical digestion of food

A. - largest . Secretes watery saliva. When infected with virus à mumps http://www.youtube.com/watch?v=5mZBz746o2E

B. middle in size. Secretes both a watery and mucousy saliva http://www.youtube.com/watch?v=uY_W1oToNJA

C. – smallest in size. Secretes mucousy saliva.

3 3. Pharynx - common openings for the respiratory and digestive systems

A. Nasopharynx - only associated with the respiratory system

B. Oropharynx – Middle division of pharynx Boundaries: fauces (opening of mouth into pharynx)- tip of epiglottis Lined with stratified squamous Common area for air, food and drink

C. Laryngopharynx Inferior division of pharynx Boundaries: tip of epiglottis àtop of esophagus Lined with stratified squamous When , pulls epiglottis down to cover/protect airway.

Food/drink channeled into esophagus.

4. Esophagus

A long muscular tube extending from the pharynx to stomach.

Consists of both skeletal and smooth muscle. Located posterior to trachea and anterior to vertebral column. Lined with stratified squamous muscle at both ends Upper esophageal sphincter * skeletal muscle Lower esophageal sphincter *smooth muscle

5. Stomach http://www.youtube.com/watch?v=ZvudWuvMjtA

An expandable muscular sack. Has 3 layers of smooth muscle Lined with simple columnar

4 Wall of stomach contains several that secrete: a) HCL b) Digestive enzymes c) Mucus

1. Cardiac region

2. fundus (dome)

3. Body a) lesser curvature

b) greater curvature

4. pyloric region

5. pyloric sphincter (boundary between stomach and small intestine)

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6. Small intestine - has 3 subdivisions a relatively long muscular tube about 10 feet diameter 1-2 inches all 3 subdivisions lined with simple columnar Lacteals found in small intestine wall.

A.

About 1 foot long Shaped like a capital “C” Inner surface highly folded with villi and microvilli to increase surface area Receives digestive enzymes from liver and pancreas

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B.

About 3 feet long with many tightly folded curves = flexure Inner surface highly folded with villi and microvilli to increase surface area.

C.

About 6 feet long Has many flexures No obvious boundary between jejenum and ileum Inner surface highly folded with villi and microvilli to increase surface area.

= a sphincter muscle *boundary between small & large intestines.

7 7. Large Intestine - has 4 subdivisions

A relatively short muscular tube About 5 feet long Diameter = 6 cm (3 inches) First 3 subdivisions lined with simple columnar. Exception: .

A.

A blind pouch or sack Function: storehouse of intestinal bacteria

Appendix attached

B. Colon * has 4 subdivisions* (see diagram)

1.

8 2. 3. 4.

3 long thin bands of smooth muscle along entire length of colon When contract, causes the colon to pleat. Each pleat = . Haustra (pl)

C.

A short muscular tube about 4-5 inches long Located with in pelvic cavity Function: temporary storage of prior to egestion.

D. Anal canal

A short muscular tube about 1-2inches long. Lined with stratified squamous. Protection from abrasion. Two sphincter muscles 1) *smooth muscle ( involuntary) 2) *skeletal muscle (potty training)

9 3) Anal canal ends at opening to external environment – .

8. Accessory organs of the digestive system A. Liver

The largest internal organ of body Dozens of important physiologic functions Two major lobes (left and right) Two minor lobes (caudate and quadrate Major digestive function: produces and secretes bile Bile travels through common hepatic duct àcommon bile ductà duodenum

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B. Gall bladder

A small sac on inferior side of liver Functions: 1. temporary storage of bile overproduced by liver 2. concentration of bile while being stored. When needed, bile is released through cystic duct (unites with common hepatic duct) into duodenum

C. Pancreas

A long slender organ with a bumpy surface Located within C-shape of duodenum Two major junctions: 1. Endocrine – production of insulin and glucagon 2. Exocrine – produces several digestive enzymes. Enzymes travel through pancreatic duct into duodenum.

Quiz #1

11 9. Digestion of Ingested Food - 2 methods of digestion:

mechanical digestion =

Physically breaking large pieces of food into many smaller pieces Increases surface area

chemical digestion =

Breaking chemical bonds within food particles

Proteins à amino acids

Carbohydrates à glucose

10. DIGESTION: Oral cavity, pharynx, and esophagus

Mechanical digestion begins when teeth grind food into smaller pieces (mastication)

Chemical digestion begins when salivary glands secrete saliva, which contains salivary amylase

Begins chemical breakdown of carbohydrates Glands in tongue secrete tiny amount of enzyme lipase to begin chemical digestion of lipids

Food is pressed into a loose ball by tongue (bolus)

12 11. Swallowing A. voluntary stage Bolus is pushed by tongue posteriorly through fauces into oropharynx. Bolus hits uvula, which is a “trip-wire” to initiate involuntary stage

B. involuntary stage - *reflex

Once in oropharynx, bolus is moved inferiorly through the rest of pharynx by a series of smooth muscles that encircle pharynx (pharyngeal constrictor muscles)

Epiglottis is pulled down to protect airway Bolus pass through upper esophageal sphincter Peristalsis moves bolus down esophagus Bolus passes through lower esophageal sphincter into stomach

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14 12. DIGESTION: Stomach A. mechanical digestion

Smooth muscle in stomach wall contracts to push bolus back and forth in churning motion (mixing waves) Similar to swishing mouthwash!

= Liquified food in stomach. Has thin watery consistency

B. chemical digestion

Salivay amylase and lingual lipase still working but soon inactivated by stomach acid

1) HCl – denatures proteins (breaks 3-D structure

2) pepsin – digests proteins – small polypeptides

3) gastric lipase – digests fats/lipids àtriglycerides

4) mucus – protects stomach itself from being digested!

13. ABSORPTION: Stomach

Small amount of water absorbed Most all alcohol absorbed

14. Liver

Produces about 1 liter of bile /day Function: breaks large globs of fat into many smaller globs of fat (emulsification) A form of mechanical digestion which increases surface area so lipase can work more efficiently. Bile sent through a common hepatic duct àcommon bile ductà duodenum

15 Excess bile rerouted into gall bladder for storage.

15. Pancreas Secretes a combination of digestive enzymes called: pancreatic juice

Pancreatic juice sent through pancreatic duct into duodenum It is basic so it neutralizes stomach acid.

A. pancreatic amylase – continues carbohydrate digestion

B. trypsin – continues protein digestion

C. pancreatic lipase – continues lipid digestion

16. DIGESTION: Small intestine chyme passes through pyloric sphincter into small intestine

A. mechanical digestion - 2 processes:

Peristalisis – pushes chyme through entire small intestine

Segmentation – swishing chyme back and forth in short segments of intestine

Both forms of mechanical digestion increase chances of substrate mixing with enzymes.

B. chemical digestion

Digestive enzymes from liver, gall bladder and pancreas are delivered into duodenum

Most all-remaining chemical digestion occurs in duodenum

1. amylase (carbohydrates) à glucose

16 2. pepsin and trypsin (proteins) à amino acids 3. lipase and bile (lipids) à glycerol and fatty acids

17. ABSORPTION: small intestine Most all-remaining absorption of nutrients occurs in jejunum and ileum -Villi and microvilli increase surface area to maximize absorptive process -absorption occurs via passive passive transport: simple diffusion & osmosis and active transport- facilitated diffusion

18. DIGESTION: Large intestine

What remains of chyme passes through ileocecal valve àlarge intestine Material solidifies to form feces.

A. mechanical digestion Contraction of causes haustra to appear. Haustra mixes feces with intestinal bacteria (E-coli)

B. chemical digestion

Final bit of chemical digestion is done by E-coli. These bacteria use any remaining sugar as their food source. Waste products of bacteria: methane gas and hydrogen sulfide Bacteria also produce helpful metabolites for the human body (vitamins K, B6, Folic Acid) – the release of gas

19. ABSORPTION: large intestine

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*Most all-remaining water absorption occurs here

If too much water is absorbed by body the feces become dry (constipation If too little water is absorbed by body the feces become too wet - diarrhea

20. Egestion from large intestine

Feces now solid or semi-solid in consistency Consists of 1. undigested food (cellulose) 2. dead intestinal lining cells 3. dead E-coli 4. Water 5. Ions Egestion accomplished via reflex

1. peristalsis pushes feces into rectum, where it stretches wall of rectum (stimulus) 2. internal anal sphincter relaxes 3. if person is ready, voluntary relaxation of external anal sphincter 4. peristalsis pushes feces out of body through anus.

21. Disorders of the digestive system A. peptic ulcer

An open sore or lesion in the lining of stomach or duodenum Caused by: too much stomach acid, stress, poor diet or bacterial infection Symptoms: indigestion, stomach pain, internal bleeding, vomiting Treatment: modify diet, stress reduction, antacids, and antibiotics http://mdmercy.com/centers-of-excellence/digestive-health-and-liver-disease/conditions-we-treat/stomach-and- intestinal-disorders/peptic-ulcer-disease?sc_lang=en http://www.youtube.com/watch?v=SWMWsOXlBwE

B. Dysentery

18 The egestion of large amounts of loose, watery feces Much more severe than simple diarrhea Feces passes too quickly through large intestine such that normal water absorption cannot occur Can lead to dehydration àdeath Causes: bacteria in water, unsanitary conditions Treatments: improve sanitary conditions of water supply, antibiotics http://education-portal.com/academy/lesson/entamoeba-histolytica-amoebic-dysentery-causes-symptoms-treatment.html#lesson

C. colorectal cancer

Colorectal cancer is 2nd leading cancer death of men/women Cancer can affect all parts of digestive system but colon and rectum are particularly susceptible. Symptoms: pain and/or bleeding during egestion Change in bowel habits Treatment: surgery. Detection is easy with a colonoscopy (50 years – or earlier if family history) http://myfox8.com/2014/02/24/march-is-colorectal-cancer-awareness-month/

D.

Enlarged and infected that line the rectum and anal canal Passage of feces can rub the inner wall and expose these superficial blood vessels BV’s can leak blood or even burst open Symptoms: itching, burning sensation, pain Treatment: ointments, suppositories, surgical removal. http://www.youtube.com/watch?v=rVxVnZDsRHw

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