Page 7 - 86 human physiology part-2

Chapter 12

Stomach

The stomach lies between the esophagus and the first part of the small intestine (the duodenum). It
is on the left side of the abdominal cavity; the fundus of the stomach lying against the diaphragm.
Lying beneath the stomach is the pancreas. The greater omentum hangs from the greater curvature. A
mucous membrane lines the stomach which contains glands that secrete gastric juices. When food is
mixed and churned with gastric juices it forms a semi-liquid substance called chyme, which then,
through peristalsis, is pushed to the stomach and on to the small intestine.

The stomach is divided into four sections, each of which has different cells and functions. The
sections are: 1) Cardiac region, where the contents of the esophagus empty into the stomach, 2)
Fundus, formed by the upper curvature of the organ, 3) Body, the main central region, and 4) Pylorus
or atrium, the lower section of the organ that facilitates emptying the contents into the small intestine.
Two smooth muscle valves, or sphincters, keep the contents of the stomach contained. They are the: 1)
Cardiac or esophageal sphincter, dividing the tract above, and 2) Pyloric sphincter, dividing the
stomach from the small intestine. The gastric juice, which is in the stomach, is highly acidic with a pH
of 1-3. Gastric acid may cause or compound damage to the stomach wall or its layer of mucus, causing
a peptic ulcer. On the inside of the stomach there are folds of skin call the gastric rugae. Gastric rugae
make the stomach very extendable, especially after a very big meal.

Gastric Glands

There are many different gastric glands and they secret many different chemicals. Parietal cells
secrete hydrochloric acid; chief cells secrete pepsinogen; goblet cells secrete mucus; argentaffin cells
secrete serotonin and histamine; and G cells secrete the hormone gastrin.

Vessels and nerves

Arteries: The arteries supplying the stomach are the left gastric, the right gastric and right
gastroepiploic branches of the hepatic, and the left gastroepiploic and short gastric branches of
the lineal. They supply the muscular coat, ramify in the submucous coat, and are finally
distributed to the mucous membrane.

Capillaries: The arteries break up at the base of the gastric tubules into a plexus of fine
capillaries, which run upward between the tubules, anatomizing with each other, and ending in a
plexus of larger capillaries, which surround the mouths of the tubes, and also form hexagonal
meshes around the ducts.

Veins: From these the veins arise, and pursue a straight course downward, between the tubules,
to the submucous tissue; they end either in the lineal and superior mesenteric veins, or directly in
the portal vein.

Lymphatics: The lymphatics are numerous: They consist of a superficial and a deep set, and pass
to the lymph glands found along the two curvatures of the organ.

Nerves: The nerves are the terminal branches of the right and left urethra and other parts, the
former being distributed upon the back, and the latter upon the front part of the organ. A great
number of branches from the celiac plexus of the sympathetic are also distributed to it. Nerve
plexuses are found in the submucous coat and between the layers of the muscular coat as in the

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