April 18, 2007

The Human Stomach


the stomach is a bean-shaped hollow muscular organ of the gastrointestinal tract involved in the second phase of digestion, following mastication. The word stomach is derived from the Latin stomachus, which derives from the Greek word stomachos (στόμαχος). The words gastro- and gastric (meaning related to the stomach) are both derived from the Greek word gaster (γαστήρ).

The stomach is usually a highly acidic environment due to gastric acid production and secretion which produces a luminal pH range usually between 1 and 4 depending on the species, food intake, drug use, and other factors. Such an environment is able to break down large molecules (such as from food) to smaller ones so that they can eventually be absorbed from the small intestine. The stomach can produce and secrete about 2 to 3 liters of gastric acid per day.

Pepsinogen is secreted by chief cells and turns into pepsin under low pH conditions and is a necessity in protein digestion.

Absorption of vitamin B12 from the small intestine is dependent on conjugation to a glycoprotein called intrinsic factor which is produced by parietal cells of the stomach.

Other functions include absorbing water, some ions, and some lipid soluble compounds such as alcohol, aspirin, and caffeine.

The stomach lies between the esophagus and the duodenum (the first part of the small intestine). It is on the left side of the abdominal cavity. The top of the stomach lies against the diaphragm. Lying beneath the stomach is the pancreas, and the greater omentum which hangs from the greater curvature.

Two smooth muscle valves, or sphincters, keep the contents of the stomach contained. They are the Cardiac or esophageal sphincter dividing the tract above, and the Pyloric sphincter dividing the stomach from the small intestine.

The stomach is surrounded by parasympathetic (stimulant) and orthosympathetic (inhibitor) peluxes (anterior gastric, posterior, superior and inferior, celiac and myenteric), which regulate both the secretory activity and the motor activity of the muscles.

In humans, the stomach has a volume of about 50 mL when empty. After a meal, it generally expands to hold about 1 litre of food, but it can actually expand to hold as much as 4 litres. When drinking milk it can expand to just under 6 pints, or 3.4 litres. The human stomach has more nerve endings than the human brain.

The stomach is divided into four sections, each of which has different cells and functions. The sections are:

Cardia where the contents of the esophagus empty into the stomach.
Fundus formed by the upper curvature of the organ.
Body or corpus the main, central region.
Pylorus or antrum the lower section of the organ that facilitates emptying the contents into the small intestine.

Adapted from: Wikipedia