694
UNIT FIVE
5. Mixing and emptying actions
a. As the stomach f
lls, its wall stretches, but its
internal pressure remains unchanged.
b. Mixing movements aid in producing chyme;
peristaltic waves move chyme into the pylorus.
c. The muscular wall oF the pylorus regulates chyme
movement into the small intestine.
d. The rate oF emptying depends on the fl
uidity oF the
chyme and the type oF Food present.
e. The upper part oF the small intestine f
lls, and
an enterogastric refl
ex inhibits peristalsis in the
stomach.
F. Vomiting results From a complex refl
ex that has
many stimuli.
17.7
PANCREAS (PAGE 671)
The pancreas is closely associated with the duodenum.
1. Structure oF the pancreas
a. It produces pancreatic juice secreted into a
pancreatic duct.
b. The pancreatic duct leads to the duodenum.
2. Pancreatic juice
a. Pancreatic juice contains enzymes that can split
carbohydrates, proteins, Fats, and nucleic acids.
b. Pancreatic juice has a high bicarbonate ion
concentration that helps neutralize chyme and
causes the intestinal contents to be alkaline.
3. Regulation oF pancreatic secretion
a. Secretin From the duodenum stimulates the release oF
pancreatic juice that contains Few digestive enzymes
but has a high bicarbonate ion concentration.
b. Cholecystokinin From the intestinal wall stimulates
the release oF pancreatic juice that has a high
concentration oF digestive enzymes.
17.8
LIVER (PAGE 673)
The liver is located in the upper-right quadrant oF the
abdominal cavity.
1. Liver structure
a. The liver is a highly vascular organ, enclosed in a
f
brous capsule, and divided into lobes.
b. Each lobe consists oF hepatic lobules, the
Functional units oF the liver.
c. Bile From the lobules is carried by bile ductules
to hepatic ducts that unite to Form the common
hepatic duct.
2. Liver Functions
a. The liver has many Functions. It metabolizes
carbohydrates, lipids, and proteins; stores some
substances; f
lters blood; destroys toxins; and
secretes bile.
b. Bile is the only liver secretion that directly aFFects
digestion.
3. Composition oF bile
a. Bile contains bile salts, bile pigments, cholesterol,
and electrolytes.
b. Only the bile salts have digestive Functions.
c. Bile pigments are products oF red blood cell
breakdown.
2. Major salivary glands
a. The parotid glands are the largest, and they secrete
saliva rich in amylase.
b. The submandibular glands in the fl
oor oF the
mouth produce viscous saliva.
c. The sublingual glands in the fl
oor oF the mouth
primarily secrete mucus.
17.5
PHARYNX AND ESOPHAGUS (PAGE 661)
The pharynx and esophagus serve as passageways.
1. Structure oF the pharynx
a. The pharynx is divided into a nasopharynx,
oropharynx, and laryngopharynx.
b. The muscular walls oF the pharynx contain f
bers
in circular and longitudinal groups.
2. Swallowing mechanism
a. Swallowing occurs in three stages.
(1) ±ood is mixed with saliva and Forced into the
pharynx.
(2) Involuntary refl
ex actions move the Food into
the esophagus.
(3) Peristalsis transports Food to the stomach.
b. Swallowing refl
exes momentarily inhibit breathing.
3. Esophagus
a. The esophagus passes through the mediastinum
and penetrates the diaphragm.
b. Circular muscle f
bers at the distal end oF the
esophagus help prevent regurgitation oF Food From
the stomach.
17.6
STOMACH (PAGE 665)
The stomach receives Food, mixes it with gastric juice,
carries on a limited amount oF absorption, and moves
Food into the small intestine.
1. Parts oF the stomach
a. The stomach is divided into the cardia, Fundus,
body, and pylorus.
b. The lower esophageal sphincter serves as a valve
between the esophagus and the stomach.
c. The pyloric sphincter serves as a valve between
the stomach and the small intestine.
2. Gastric secretions
a. Gastric glands secrete gastric juice.
b. Gastric juice contains pepsin(begins digestion oF
proteins), hydrochloric acid, lipase, and intrinsic
Factor.
3. Regulation oF gastric secretions
a. Parasympathetic impulses and the hormone gastrin
enhance gastric secretion.
b. The three stages oF gastric secretion are the
cephalic, gastric, and intestinal phases.
c. The presence oF Food in the small intestine refl
exly
inhibits gastric secretions.
4. Gastric absorption
a. The stomach is not well adapted For absorption.
b. A Few substances such as water and other small
molecules are absorbed through the stomach wall.
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