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
SYSTEM
A. 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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4
B. Wall Structure of Alimentary Canal
1. 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)
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Wall of the Alimentary Canal
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C. Movement of the tube
2 Basic Movements:
1. Mixing—mixes food with juices secreted by the mucosa
of the stomach
2. Propelling movements—peristalsis (wavelike contractions
that force food along the digestive tube)
Mixing
Peristalsis
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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. palatine
b. 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)—20
b. secondary (permanent)—32
• F(x): mastication (chewing)
• 4 types of teeth:
a. incisors—front teeth for biting
b. canine—cone-shaped for tearing food
c. bicuspids—for grinding food particles
d. molars—for grinding food particles
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4 Types of Teeth
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• Consists of:
a. crown—part above gum
b. root—anchored to bone by cementum and periodontal
ligament
c. enamel—covers crown
--hardest substance in body
d. dentin—under enamel
--like very hard bone
e. pulp cavity—under dentin
--contains blood vessels, nerves, and CT
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Tooth
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E. Salivary Glands
1. 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 lubrication
3. 3 major pairs of salivary glands
a. parotids—in front of and below each ear
b. submandibular—in floor of mouth
c. sublingual—on floor of mouth under tongue
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Salivary Glands
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F. Pharynx
1. Common to digestive and respiratory tracts
2. Divided into 3 areas:
a. nasopharynx—passage for air during breathing
b. oropharynx—passageway for food and air
c. laryngopharynx—opens into larynx and esophagus
3. 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. Esophagus
1. Collapsed tube about 10 inches long that connects
pharynx and stomach
2. Mucous glands keep it moist and lubricated
H. Stomach
1. 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 opening
b. fundus—temporary storage area
c. body
d. 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 mucus
b. chief cells—secrete digestive enzymepepsinogen (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—protection
b. HCl—converts pepsinogen to pepsin
c. intrinsic factor—aids in absorption of vitamin B12 in
small intestine
7. 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
A. Structure
1. Elongated, flattened organ
2. 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 duct
4. Heterocrine Gland (endocrine and exocrine)
5. Exocrine Component functions in digestion
• Pancreatic acinar cells
-make up most of the pancreas
-produce pancreatic juice
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Pancreas
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LIVER
A. Structure
1. 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
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Liver
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Functions of the Liver
1. Carries out the metabolism of carbohydrates, lipids, and
proteins
2. Storage
• Stores glycogen (animal starch), iron, blood, and
vitamins A, D, B12
3. Blood filtering
•Removal of damaged red blood cells and foreign
substances
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III. GALLBLADDER
A. Structure
1. Pear-shaped sac on the inferior surface of the liver
2. 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. Functions
1. Store bile
2. Concentrate bile by reabsorbing water
3. Release bile into small intestine
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Gallstones
1. Crystals formed from cholesterol in bile
2. Can block bile flow, cause pain, and result removal of
gallbladder
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SMALL INTESTINE
A. Structure
1. Tubular organ about 20 feet long
2. Joins the stomach at the pyloric sphincter
3. Joins the large intestine at the ileocecal junction
4. 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 Intestine
1. Completes digestion
2. Absorbs products of digestion
3. Receives secretions from pancreas and liver
4. Transports residues to large intestine
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V. LARGE INTESTINE
A. Structure
1.
2.
5 feet long
4 Divisions of Large Intestine
a. Cecum
 First
2-3 inches
 Blind 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. Rectum
 From
colon to anal canal
d. Anal Canal
 Last
1-2 inches of large intestine
 Anus
-opening on distal end of anal canal
-controlled by 2 sphincter muscles:
internal anal sphincter-involuntary
external anal sphincter-voluntary
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Large Intestine
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B. Functions of the Large Intestine
1.
2.
3.
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secrete mucus
reabsorb water and electrolytes
store and eliminate waste
C. Feces
1.
2.
3.
4.
5.
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Solid waste
Undigested or unabsorbed material
75% water
Color due to bile pigments
Odor from bacterial activity