I. Organization and Function

A. Digestion: process of altering chemical and physical composition of food so that it can be absorbed by body cells.

B. Function: prepare for food for absorption and use by body cells.

C. Alimentary Canal: tube open at both ends running through ventral cavities of body.

D. Wall of gastrointestinal tract

1. mucosa: mucous lining.

2. submucosa: submucous coat of connective tissue containing blood vessels.

3. muscularis: muscular layer made of circular and longitudinal layers.

4. serosa: fibroserous layer.

II. Organs of the Digestive System

A. Mouth

1. Lips

2. Cheeks

3. Hard palate

4. Soft palate: soft arch-shaped muscle.

5. Tongue

a. regions

i. root

ii. tip

iii. body

b. papillae

i. circumvallate

ii. fungiform

iii. filiform

6. Salivary glands

a. parotids

i. location: in front and below the ear.

ii. serous saliva with enzymes but no mucus.

b. submandibulars

i. location: just below mandibular angle.

ii. serous and mucous secretions in saliva.

c. sublinguals

i. location: under mucosa of floor of mouth.

ii. mucous secretions in saliva.

d. buccal glands

i. location: mucosa lining cheeks and mouth.

7. Teeth

a. Structure

i. Crown

ii. Neck

iii. Root

b. Coverings

i. enamel

ii. cementin

iii. dentin

a. greatest proportion of the tooth shell.

b. contains pulp cavity.

1. connective tissue.

2. blood and lymph vessels.

3. sensory nerves.

c. Types of teeth

i. deciduous teeth

a. 20 teeth

b. eruption of first tooth usually at 6 months

c. shed between 6-13 years

ii. permanent teeth: 32 teeth

a. incisors: used for cutting.

b. canines: used for tearing.

c. premolars: used for grinding.

d. molars: used for grinding.

B. Pharynx

C. Esophagus

1. structure

a. collapsible tube approximately 25 cm long.

b. 2 Muscle layers

i. inner muscles: circular fibers.

ii. outer muscles: longitudinal fibers.

c. Muscle types

i. upper 1/3: striated muscle.

ii. middle 1/3: mixed striated and smooth muscle.

iii. lower 1/3: smooth muscle.

2. location

a. posterior to the trachea and heart.

b. extends to the stomach, piercing the diaphragm.

D. Stomach

1. structure

a. elongated pouch the size of a large sausage when empty. holds 1.0-1.5 L.

b. Stomach Wall

i. epithelial lining

a. rugae

b. gastric pits

c. gastric glands

1. chief cells

2. parietal cells

ii. gastric muscles

c. Divisions of stomach

i. fundus: elongated portion to the left and above the opening of the esophagus.

ii. body: central portion.

iii. pylorus: lowest portion.

d. Curves of stomach

i. lesser curvature: upper right surface.

ii. greater curvature: lower left surface.

f. Sphincter muscles

i. cardiac sphincter: opening of the esophagus into the stomach.

ii. pyloric sphincter: opening from the pyloric portion into the duodenum.

2. location

a. upper abdominal cavity

b. under liver and diaphragm

3. functions

a. food reservoir

b. secretes gastric juice

c. churns food

d. secretes intrinsic factor

e. some absorption

f. produces gastrin

g. destroys pathogenic bacteria.

E. Small Intestine

1. structure

a. Small Intestine Wall

i. villi containing an arteriole, a venule, and a lacteal.

ii. microvilli: brush border.

b. Divisions of the small intestine

i. duodenum

ii. jejunum

iii. ileum

2. function: digestion.

F. Large Intestine

1. structure

a. Divisions

i. Cecum

ii. Colon

a. Ascending colon

b. Transverse colon

c. Descending colon

d. Sigmoid colon

iii. Rectum

b. Large Intestine Wall

i. mucous glands

ii. muscles

a. Taeniae coli: longitudinal muscles grouped in tape like strips.

b. Haustra: pouches created by circular muscles grouped into rings.

2. function: absorption.

G. Vermiform appendix

1. structure: 8-10 cm tubular, wormlike extension.

2. location: behind cecum.

3. function: filled with lymph tissue for fighting infections.

III. Linings

A. Peritoneum

1. structure: membrane holding organs loosely in place.

a. parietal layer: lines walls of abdominal cavity.

b. visceral layer: fan-shaped projection of parietal peritoneum.

B. Mesentery: fan-shaped projection of parietal peritoneum from the lumbar region of the posterior abdominal wall.

C. Greater omentum: hangs loosely over intestines.

D. Lesser omentum

IV. Accessory Organs

A. Liver

1. structure

a. lobes

b. hepatic lobules

c. bile ducts

2. functions

a. detoxifies

b. secretes bile

c. metabolism of proteins, fats, and carbohydrates

d. stores iron, vitamins A, B₁₂, and D

e. produces plasma proteins

3. Bile

B. Pancreas

1. structure

a. exocrine tissue

b. endocrine tissue

i. pancreatic islets

ii. a and b cells

2. location: in the C-shaped curve of duodenum

3. functions

a. acinar cells secrete digestive enzymes

b. b cells secrete insulin for carbohydrate metabolism

c. a cells secrete glucagon for carbohydrate metabolism

V. Physiology of the Digestive System

A. Peristalsis

B. Regulation of Motility

C. Mechanical Digestion

1. Mastication: food broken up by chewing.

2. Deglutition: swallowing bolus.

D. Chemical Digestion

1. Carbohydrate Digestion

a. Polysaccharides: converted to disaccharides by amylases in saliva and pancreatic juices.

b. Dissacharides: converted to monosaccharides by sucrase, lactase, and maltase.

2. Protein Digestion

a. proteases: hydrolyze proteins.

b. gastrin contains pepsin.

c. pancreatic juice contains trypsin.

d. peptidases located in brush border.

3. Fat Digestion: emulsification is required due to insolubility of lipids.

a. bile emulsifies fats in the small intestine.

b. pancreatic lipase digests fats in small intestine

E. Control of digestive gland secretion

1. Salivary secretion

2. Gastric secretion

3. Pancreatic Secretion

4. Bile

F. Absorption

G. Elimination of residues of digestion

VI. Nutrition and Metabolism

A. Carbohydrates

1. dietary sources

2. metabolism

3. Control of glucose metabolism

B. Lipids

1. triglycerides; phospholipids; cholesterol

2. Lipoproteins travel in bloodstream

3. Essential fatty acids: unsaturated fatty acids that must be supplied by the body.

C. Proteins

1. amino acids

a. 12 amino acids can be synthesized by the body.

b. 8 essential amino acids must be obtained from the diet.

2. protein metabolism

D. Vitamins

1. organic molecules needed in small quantities for normal metabolism.

2. Fat soluble: A,D,E,K.

3. Water soluble: B, C.

E. Minerals

1. inorganic elements and salts

anatomy page