Page 8 - 86 human physiology part-2

The Gastrointestinal System

intestine. From these plexuses fibrils are distributed to the muscular tissue and the mucous
membrane.

Disorders of the Stomach

Disorders of the stomach are common. There can be a lot of different causes with a variety of
symptoms. The strength of the inner lining of the stomach needs a careful balance of acid and mucus. If
there is not enough mucus in the stomach, ulcers, abdominal pain, indigestion, heartburn, nausea and
vomiting could all be caused by the extra acid.

Erosions, ulcers, and tumors can cause bleeding. When blood is in the stomach it starts the
digestive process and turns black. When this happens, the person can have black stool or vomit. Some
ulcers can bleed very slowly so the person won't recognize the loss of blood. Over time, the iron in
your body will run out, which in turn, will cause anemia.

There isn't a known diet to prevent against getting ulcers. A balanced, healthy diet is always
recommended. Smoking can also be a cause of problems in the stomach. Tobacco increases acid
production and damages the lining of the stomach. It is not a proven fact that stress alone can cause an
ulcer.

Histology of the human stomach

Like the other parts of the gastrointestinal tract, the stomach walls are made of a number of layers.

From the inside to the outside, the first main layer is the mucosa. This consists of an epithelium,
the lamina propria underneath, and a thin bit of smooth muscle called the muscularis mucosa.

The submucosa lies under this and consists of fibrous connective tissue, separating the mucosa
from the next layer, the muscularis externa. The muscularis in the stomach differs from that of other GI
organs in that it has three layers of muscle instead of two. Under these muscle layers is the adventitia,
layers of connective tissue continuous with the omenta.

The epithelium of the stomach forms deep pits, called fundic or oxyntic glands. Different types of
cells are at different locations down the pits. The cells at the base of these pits are chief cells,
responsible for production of pepsinogen, an inactive precursor of pepsin, which degrades proteins. The
secretion of pepsinogen prevents self-digestion of the stomach cells.

Further up the pits, parietal cells produce gastric acid and a vital substance, intrinsic factor. The
function of gastric acid is two fold 1) it kills most of the bacteria in food, stimulates hunger, and
activates pepsinogen into pepsin, and 2) denatures the complex protein molecule as a precursor to
protein digestion through enzyme action in the stomach and small intestines. Near the top of the pits,
closest to the contents of the stomach, there are mucous-producing cells called goblet cells that help
protect the stomach from self-digestion.

The muscularis externa is made up of three layers of smooth muscle. The innermost layer is
obliquely-oriented: this is not seen in other parts of the digestive system: this layer is responsible for
creating the motion that churns and physically breaks down the food. The next layers are the square and
then the longitudinal, which are present as in other parts of the GI tract. The pyloric antrum which has
thicker skin cells in its walls and performs more forceful contractions than the fundus. The pylorus is

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