I. BASIC FUNCTIONS OF THE DIGESTIVE TRACT

A. Digestion—process of altering the physical state and chemical composition of food so that the body’s cells can use it

B. Absorption—process by which small digested molecules pass through the cells of the intestinal tract, entering the blood and lymph

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II. ANATOMY OF DIGESTIVE SYSTEMA. Components

1. Alimentary Canal• Mouth• Pharynx• Esophagus• Stomach• Small intestine• Large intestine

2. Accessory Organs• Salivary glands• Liver• Gallbladder• Pancreas

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Alimentary Canal

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B. Wall Structure of Alimentary Canal1. Alimentary canal is a muscular tube, 30 feet long, and

located in the ventral body cavity.2. Has the same four layers throughout:

a. Mucosa •Innermost layer

b. Submucosa• Loose CT with blood vessels, glands, lymph vessels,

and nerves c. Muscularis mucosa

• 2 layers of smooth muscle d. Serosa

• Outermost layer (visceral peritoneum) 5

Wall of the Alimentary Canal

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C. Movement of the tube2 Basic Movements:1. Mixing—mixes food with juices secreted by the mucosa

of the stomach2. Propelling movements—peristalsis (wavelike contractions

that force food along the digestive tube)

Mixing Peristalsis7

D. Oral Cavity

1. Mouth•Receives food•Prepares food for digestion (breaks food into small

particles and mixes it with saliva) 2. Tongue

•Mostly muscle•Anchored to midline of the floor of the mouth by the

frenulum•Covered with papillae which contain taste buds•Movement aids in mixing food and saliva and moving

food toward the rear of the mouth

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3. Palate• Forms roof of the mouth• Consist of hard anterior part (hard palate) and soft

posterior part (soft palate)• Uvula—cone-shaped projection that hangs down from

soft palate and pulls upward when swallowing to prevent food from entering the nasal cavity

4. Tonsils • Masses of lymphatic tissue• 3 tonsil masses:

a. palatineb. pharyngeal (adenoids)c. lingual

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Oral Cavity

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Tonsils

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5. Teeth• 2 sets

a. primary (deciduous)—20b. secondary (permanent)—32

• F(x): mastication (chewing)• 4 types of teeth:

a. incisors—front teeth for bitingb. canine—cone-shaped for tearing foodc. bicuspids—for grinding food particlesd. molars—for grinding food particles

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4 Types of Teeth

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• Consists of:a. crown—part above gumb. root—anchored to bone by cementum and periodontal

ligamentc. enamel—covers crown

--hardest substance in bodyd. dentin—under enamel

--like very hard bonee. pulp cavity—under dentin

--contains blood vessels, nerves, and CT

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Tooth

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E. Salivary Glands1. F(x):

•To secrete saliva which moisten food and begins carbohydrate digestion•Cleanses mouth and teeth•Dissolves food for taste

2. Consists of serous cells which produce amylase (enzyme that breaks down starch and glycogen) and mucous cells which secrete mucus for lubrication3. 3 major pairs of salivary glands

a. parotids—in front of and below each earb. submandibular—in floor of mouthc. sublingual—on floor of mouth under tongue

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Salivary Glands

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F. Pharynx1. Common to digestive and respiratory tracts2. Divided into 3 areas:

a. nasopharynx—passage for air during breathingb. oropharynx—passageway for food and airc. laryngopharynx—opens into larynx and

esophagus3. F(x):

• Swallowing (deglutition)-Voluntary but becomes involuntary as swallowing reflex is initiated-Involves chewing and bolus (ball of partially digested food) formation

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Pharynx

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G. Esophagus1. Collapsed tube about 10 inches long that connects pharynx and stomach2. Mucous glands keep it moist and lubricated

H. Stomach1. Anatomy

• “J” shaped pouch-like organ just under the diaphragm in the upper left portion of abdominal cavity

• Inner mucosa forms folds called rugae

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2. F(x):• Receive food• Mix food with gastric juice• Initiate protein digestion• Limited absorption• Transport partially digested food to small intestine

3. Divided into 4 regions:a. cardiac—near esophageal openingb. fundus—temporary storage areac. bodyd. pylorus—enters small intestine

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Stomach

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4. Mucosa is thick with many gastric glands.5. Gastric glands contain 3 types of secretory cells:

a. goblet cells—secrete mucusb. chief cells—secrete digestive enzyme-

pepsinogen (inactive form of pepsin which digest proteins)

c. parietal cells—secrete hydrochloric acid (HCl) and intrinsic factor

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Gastric Gland (Lining of Stomach)

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6. F(x) of gastric gland secretions:a. mucus—protectionb. HCl—converts pepsinogen to pepsin c. intrinsic factor—aids in absorption of vitamin B12 in small intestine7. Regulation of Gastric Secretion

• Under nerve and hormone control• Gastrin (stomach hormone) increases release of gastric juices

8. Substances absorbed in stomach:• water• glucose• alcohol• aspirin• lipid-soluble drugs

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9. Mixing and Emptying of Stomach• Mixing produces chyme (semisolid paste) and

peristalsis moves it to the pylorus• Rate of emptying depends on the type of food present• Liquids pass through rapidly• Solids remain until well mixed with gastric juices• Fatty food remains the longest• Carbohydrates pass through the fastest

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PANCREAS

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A. Structure1.Elongated, flattened organ2.Extends horizontally across the posterior abdominal wall in

the C-shaped curve of the duodenum 3.Pancreatic secretions enter the duodenum(small intestine)

through the pancreatic duct4. Heterocrine Gland (endocrine and exocrine)5. Exocrine Component functions in digestion•Pancreatic acinar cells

-make up most of the pancreas-produce pancreatic juice

Pancreas

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LIVER

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A. Structure1. Macroscopic• Reddish-brown in color • Enclosed in a fibrous capsule• Well supplied with blood vessels• Located in the upper right side of the abdominal cavity

inferior to the diaphragm• Divided into 2 lobes (large right lobe and smaller left lobe)

2. Microscopic• Each lobe is separated into many tiny hepatic lobules

(functional unit of liver)• Each lobule has many hepatic (cuboidal) cells radiating

outward from a central vein

Liver

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Functions of the Liver1.Carries out the metabolism of carbohydrates, lipids,

and proteins2.Storage•Stores glycogen (animal starch), iron, blood, and

vitamins A, D, B12

3. Blood filtering•Removal of damaged red blood cells and foreign substances

III. GALLBLADDER

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A. Structure1. Pear-shaped sac on the inferior surface of the liver2. Lined with epithelial cells 3. Wall contains a strong, muscular layer 4. Connects to cystic duct which joins with the common

hepatic duct to form the common bile duct which empties into the duodenum

B. Functions1. Store bile2. Concentrate bile by reabsorbing water3. Release bile into small intestine

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Gallstones1. Crystals formed from cholesterol in bile2. Can block bile flow, cause pain, and result removal of gallbladder

SMALL INTESTINE

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A. Structure1. Tubular organ about 20 feet long2. Joins the stomach at the pyloric sphincter3. Joins the large intestine at the ileocecal junction4. 3 Divisions:•duodenum~10 inches long and 2 in. in diameter (fixed)•jejunum~8 feet long•ileum~12 feet long

5. Jejunum and ileum are suspended by the mesentery (tissue containing blood vessels, nerves, and lymphatic vessels that supply the intestinal wall)

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Functions of the Small Intestine1. Completes digestion2. Absorbs products of digestion3. Receives secretions from pancreas and liver 4. Transports residues to large intestine

V. LARGE INTESTINE

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A. Structure1. 5 feet long2. 4 Divisions of Large Intestine

a. CecumFirst 2-3 inchesBlind pouch to which is attached the vermiform appendix (lymphatic tissue which has no digestive function)

Opening between ileum and cecum controlled by ileocecal valve

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b. Colon (4 parts)Ascending (right side)Transverse (longest part)Descending (left side)Sigmoid (S-shaped)

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c. RectumFrom colon to anal canal

d. Anal CanalLast 1-2 inches of large intestineAnus

-opening on distal end of anal canal-controlled by 2 sphincter muscles:

internal anal sphincter--involuntaryexternal anal sphincter--voluntary

Large Intestine

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B. Functions of the Large Intestine1. secrete mucus2. reabsorb water and electrolytes3. store and eliminate waste

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C. Feces1. Solid waste2. Undigested or unabsorbed

material3. 75% water4. Color due to bile pigments5. Odor from bacterial activity