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I.
II.
III.
IV.
Body systems used in digestion and absorption
A. From cells to organ systems
Circulatory system
A. Portal circulation
B. Lymphatic circulation
Regulatory (control) systems
A. Hormonal system
B. Nervous system
The anatomy and physiology of digestion
A. The flow of digestion
1. Mouth
a. Saliva
b. Mucus: lubricate
c.
Enzymes: carbohydrates
d. Chewing: break up, increase surface area
e. Tongue aids chewing
f. Taste receptors
2. Esophagus
a. Epiglottis
b. Trachea
3. Stomach
a. Four-cup holding tank
b. Secretes acid
c.
Secretes enzymes
d. Churns and mixes food
e. Holds food for two to four hours
4. Small intestine (about 10 feet)
a. Duodenum, first 10 inches
b. Jejunum, next four feet
c.
Ileum, last five feet
d. Most digestion is completed in the jejunum
e. Most digestive enzymes from intestine cells and
pancreas
f. Muscular contraction move and mix food
g.
Meal remains 3 to 10 hours
5. Large intestine: Colon
a. 3 1/2 feet long
b. Five sections: cecum, ascending, transverse,
descending, and sigmoid
c.
Some digestion of leftover plant fibers
d. Little other digestion
e. Food remnants and wastes stay for about 24 to 72
hours
6. Rectum and anus
7. Accessory organs
a. Liver produces bile
V.
VI.
b. Gallbladder stores bile
8. Pancreas provides enzymes and other products
B. GI tract control valves: sphincters
1. Located throughout the intestinal tract
2. Respond to inputs from nerves, hormones, hormone-like
compounds and pressure around them
3. Upper and lower esophageal sphincters
4. Pyloric sphincter
a. Base of the stomach
b. Allows stomach contents to enter intestine a few
milliliters (1 tsp) at a time
5. Ileocecal sphincter
a. End of small intestine
b. Prevents contents of large intestine from re-entering
small intestine
6. Two anal sphincters
C.
GI tract propulsion: peristalsis
1. Caused by circular and lengthwise muscle contraction
2. Occurs in esophagus, stomach, small intestine
3. Colon has occasional mass movements
D.
Digestive enzymes
1. Definition of function
2. Most made by pancreas and small intestine
3. Sensitive to pH, temperature, and types of vitamins and
minerals
4. Specific to types of substrate
A closer look at the digestive process
A. Key digestive processes in the stomach
1. Hormone-producing cells are released in response to
thinking about or chewing food
2. Stomach cells produce acid and enzymes
3. Mucus lining protects stomach from acid
4. Chyme is formed
B. Key digestive processes in the small intestine
1. Chyme triggers the release of bicarbonate
2. Bicarbonate neutralizes acid
3. Ulcer formation; intestine lacks mucus layer
4. Pancreas releases enzymes
5. Gallbladder releases bile
Small intestine: Site for most nutrient absorption
A. Absorbs 95% of energy received from carbohydrate, protein, fat,
and alcohol
B. Large surface area promotes nutrient absorption
C.
Villi trap foodstuffs to enhance absorption
D.
Constant renewal of intestinal lining
E.
VII.
VIII.
IX.
Various hormones and other substances participate in the digestive
process
F.
Types and means of absorption
1. Absorptive cells
2. Absorption mechanisms
a. Passive absorption
b. Active absorption
The large intestine completes absorption
A. 5% of carbohydrate, protein, and fat escapes absorption
B. Some water is present; absorbed in upper half of large intestine
C.
Sodium and potassium are absorbed in the upper half of large
intestine
D.
Small amounts of undigested starches are absorbed
E. Feces formed in last third of large intestine
F.
Insufficient enzyme production or incomplete digestion can cause
abdominal discomfort
Excretory system
A. Kidneys, digestive tract, skin, and lungs remove wastes for the
body
B. Excess water-soluble nutrients and other substances are filtered
and excreted
Storage systems
A. Fat - adipose (fat) tissue
B. Carbohydrate - blood, muscle, and liver
C.
Protein - blood
D.
Vitamins and minerals - liver
1. Supplements such as Vitamins A and D can cause harmful
side effects