The stomach, which receives food from the esophagus, is located
in the upper left quadrant of the abdomen. The stomach is divided
into the fundic, cardiac, body, and pyloric regions. The lesser
and greater curvatures are on the right and left sides, respectively,
of the stomach.
Gastric Secretions
The mucosal lining of the stomach is simple columnar epithelium
with numerous tubular gastric glands. The gastric glands open to
the surface of the mucosa through tiny holes called gastric pits.
Four different types of cells make up the gastric glands:
- Mucous cells
- Parietal cells
- Chief cells
- Endocrine cells
The secretions of the exocrine gastric glands - composed of the
mucous, parietal, and chief cells - make up the gastric juice. The
products of the endocrine cells are secreted directly into the bloodstream
and are not a part of the gastric juice. The endocrine cells secrete
the hormone gastrin, which functions in the regulation of gastric
activity.
Regulation of Gastric Secretions
The regulation of gastric secretion is accomplished through neural
and hormonal mechanisms. Gastric juice is produced all the time
but the amount varies subject to the regulatory factors. Regulation
of gastric secretions may be divided into cephalic,
gastric, and intestinal phases. Thoughts and smells of food start
the cephalic phase of gastric secretion; the presence of food in
the stomach initiates the gastric phase; and the presence of acid
chyme
in the small intestine begins the intestinal phase.
Stomach Emptying
Relaxation of the pyloric sphincter allows chyme to pass from the
stomach into the small intestine. The rate of which this occurs
depends on the nature of the chyme and the receptivity of the small
intestine.
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