Unit 9 B – Lower Digestive System
I. Stomach
a. Primary Organ / Chemical Digestion
i. Lies in upper part of abdominal cavity just under the diaphragm.
ii. Pouchlike structure which is able to expand.
iii. Food enters stomach through cardiac sphincter (muscular structure which keeps food from reentering esophagus).
iv. Food mixes with gastric juice (HCL acid) to form semisolid mixture called chyme.
b. Three divisions of stomach
i. Fundus – Enlarged portion to left of and above opening of esophagus.
ii. Body – Central portion of stomach.
iii. Pylorus – Lower, narrow portion which joins first part of small intestine.
1. Pyloric sphincter – Muscle which closes off opening to small intestine.
2. Rugae – Folds in stomach when stomach is empty.
II. Small Intestine
a. Primary Organ / Chemical and Physical Digestion
b. Smaller in diameter but longer than large intestine.
c. 3 Sections
i. Duodenum
ii. Jejunum
iii. Ileum
1. Contains smooth muscle that contract to cause peristalsis.
2. Lining is made up of mucous membranes which contain intestinal glands for secretion of digestive juices.
3. Villi – Fingerlike projections which absorb sugars and amino acids.
III. Liver and Gallbladder
a. Accessory organs / Chemical Digestion
i. Produces (liver) and stores (gallbladder) bile.
ii. Bile is secreted into ducts which emulsifies (breaks down) fat in chyme.
iii. Fats in chyme stimulate production of cholecystokinin (CCK) which cause contraction of gallbladder and bile flow into duodenum.
IV. Pancreas
a. Accessory Organ / Chemical Digestion
i. Lies behind stomach in C-shape created by duodenum.
ii. Contains pancreatic juice which digests most major foods.
iii. Contains sodium bicarbonate (alkaline solution) which neutralizes HCL acid in gastric juice as it enters intestines.
V. Large Intestine
a. Primary Organ / Physical Digestion
i. Forms lower portion of digestive tract.
ii. Undigested food material enters through ileocecal valve.
iii. Water and salts have been absorbed and is waste is called feces.
iv. Bacteria are added to release Vitamin K and B-complex.
v. Normal passage takes between 3-10 hours.
vi. Any faster and water is not resorbed – Diarrhea
vii. Any slower and too much water is resorbed – Constipation
b. In order in which waste passes
i. Cecum
ii. Ascending Colon
iii. Transverse Colon
iv. Descending Colon
v. Sigmoid Colon
vi. Rectum
vii. Anal Canal
VI. Appendix
a. Wormlike tubular organ which has no digestive function but contains lymphatic tissue.
b. Attached to cecum.c. Inflammation results in appendicitis.
VII. Peritoneum
a. Large, moist sheet of membrane that lines abdominal cavity.
b. 2 Layers and a Space
i. Parietal Peritoneum – Lines the cavity
ii. Visceral Peritoneum – Covers the organs
iii. Peritoneal Space – Area between layers.
VIII. Extensions of Digestive System
a. Mesentery – Anchors small intestine to posterior abdominal wall.
b. Greater omentum – Pouchlike extension of vicseral peritoneum covering lower stomach, duodenum, and transverse colon.
IX. Digestion
a. Mechanical / Physical
i. Mastication, Swallowing, Peristalsis, and Defecation
b. Chemical
i. Catalysis by enzymes in saliva and gastric, pancreatic, and intestinal juices.
X. Carbohydrate Digestion
a. Body’s primary source of energy.
i. Done by enzymes in small intestine and pancreas.
ii. Amylase changes starch to maltose.
iii. Intestinal enzymes (maltase, sucrase, and lactase) converts maltose, sucrose, and lactose to glucose.
XI. Fat Digestion
a. Body’s second source of energy.
b. Done in duodenum by bile.
c. Pancreatic lipase splits fat molecules into fatty acids and glycerol.
XII. Protein Digestion
a. Body’s last source of energy.
b. Done in stomach.
c. Renin and pepsin in gastric juice break down protein into amino acids.
XIII. Absorption
a. Food (glucose, amino acids, fatty acids, and glycerol) move through mucous membranes of small intestine into blood and lymph.
XIV. Metabolism
a. Body’s delivery and use or storage by body cells.