CHAPTER 6-THE DIGESTIVE SYSTEM
I. THREE MAJOR FUNCTIONS OF THE DIGESTIVE SYSTEM
A. Digestion-the process of breaking down food into smaller pieces for absorption.
1. Mechanical digestion-processes that rip and tear food into smaller pieces.
2. Chemical digestion-the use of enzymes, chemicals and hormones to breakdown
food materials.
B. Absorption-the movement of food materials into the bloodstream.
C. Elimination-the removal of wastes materials.
II. THE ALIMENTARY CANAL-includes the organs that form a tube for the passage of food.
A. The alimentary canal begins at the mouth and passes through the following structures to
the anus: pharynx, esophagus, stomach, small intestine, large intestine.
B. Accessory Digestive Structures-organs that play a role in digestion but they are not located
directly along the alimentary canal.
III. THE MAJOR STRUCTURES THAT FORM THE ALIMENTARY CANAL
A. The Mouth-involved in ingesting food. Muscles of the cheeks and the tongue aid in
positioning food in the mouth.
1. Processes that occur in the mouth include: mastication (chewing) and deglutition
(swallowing).
2. The hard palate-front, hard portion of the roof of the mouth. Covered by rugae.
3. The soft palate-posterior portion of the roof of the mouth. Contains the uvula which
prevents food from moving into the nasopharynx during swallowing.
4. Salivary glands-empty into the mouth. These produce enzymes (such as amylase) that
begin the process of chemical digestion.
5. The Teeth-covered by hard enamel. These rip and tear food into pieces (mastication).
a. The inner structural material of the tooth is known as the dentin. Inside of the
dentin is the pulp which contains blood vessels and nerves.
6. The Tongue-positions food for chewing and is involved in swallowing (deglutition).
B. The Pharynx-the throat. Connects to the esophagus (food tube).
1. Epiglottis-small flap that forces food into the esophagus, away from the trachea.
C. The Esophagus-tube that connects to the stomach.
1. Esophageal sphincter-small muscle between the esophagus and stomach that prevents
reflux.
D. The Stomach-organ located in the abdominal cavity that receives food from the esophagus.
1. The stomach is made up of 4 regions: the cardiac region, the fundus, the body and
the pyloric region.
2. The stomach is the primary site for chemical digestion. The stomach secretes a
number of enzymes (including pepsin) and hydrochloric acid to breakdown food.
3. In the stomach, food is converted into a semisolid material known as chyme.
4. Rugae-folds in the inner wall of the stomach. These stretch as the stomach fills.
5. Pyloric Sphincter-muscle that separates the stomach and the duodenum of the small
intestine. This muscle also regulates the flow of chyme from the stomach to the
duodenum.
6. Food and chyme are pushed out of the stomach by a type of smooth muscle
contraction known as Peristalsis. Peristalsis continues into the small intestine
and large intestine.
E. The Small Intestine-is involved in completing digestion and this structure is the primary site
for nutrient and mineral absorption.
1. 3 Regions of the Small Intestine:
a. The Duodenum-attaches to the stomach at the pyloric sphincter. This portion
of the small intestine is about 10 inches long.
b. The Jejunum-site where digestion continues. This region is 8 feet long.
c. The Ileum-connects to the large intestine. This section is 12 feet long.
2. Internal Structure of the Small Intestine
a. Villi-fingerlike projections that absorb nutrients.
F. The Large Intestine-serves as a passageway for waste materials. Is about 5 feet long.
1. Parts of the Large Intestine:
a. Cecum-small pouch near the ileocecal valve (point of connection between
the small and large intestine.
1. Vermiform appendix-near cecum, is composed of lymphatic tissue.
It has no real function.
b. The Colon-which includes the ascending colon, transverse colon, descending
colon and sigmoid colon.
2. The large intestine carries wastes products from digestion to the rectum which
empties into the anus prior to defecation.
3. Bacterial flora-bacteria (e-coli) live in the large intestine. These bacteria breakdown
small particles that enter the large intestine. The bacteria release Vitamin K and
methane.
IV. ACCESSORY STRUCTURES OF DIGESTION
A. The Liver-organ located in the right, upper quadrant of the abdominal cavity. It weighs
about three pounds. The liver is the largest glandular structure in the body.
1. The Hepatic Portal Blood System-blood vessels that bring nutrient rich blood from
the small intestine to the liver. The liver removes nutrients from this blood and
prepares them for use in the body.
2. The liver also produces bile which is helpful in digesting fat molecules.
3. Additional functions of the liver include:
a. Maintaining normal sugar levels in the body.
b. Storing vitamins for the body.
c. Converting sugar into glycogen (stored energy).
B. The Gallbladder-located under the liver. The gallbladder is a small bag that stores bile.
1. This bile is released into the small intestine where it aids in fat digestion.
2. The gallbladder releases bile through the Cystic Duct. This duct combines with the
Hepatic Duct of the liver to form the Common Bile Duct. The Common Bile Duct
empties into the duodenum of the small intestine.
C. The Pancreas-produces a number of enzymes into the small intestine. These enzymes aid in
chemical digestion in the small intestine. The enzymes empty into the duodenum via the
Pancreatic Duct.
V. COMBINING FORMS/SUFFIXES/PREFIXES-pages 131-134.
VI. PATHOLOGY
A. Peptic Ulcer Disease
B. Ulcerative colitis
C. Hernia
D. Intestinal Obstruction
E. Hemorrhoids
F. Hepatitis
G. Divertiuclosis
VII. DISEASES/CONDITIONS-pages 140-149.
VIII. PHARMACOLOGY-page 150.