Stomach

The stomach is a muscular, hollow, dilated part of the digestive system which functions as an important organ of the digestive tract. It is involved in the second phase of digestion, following mastication (chewing).

In most vertebrates, the stomach is located between the esophagus and the small intestine. It secretes protein-digesting enzymes called proteases and strong acids to aid in food digestion, (sent to it via esophageal peristalsis) through smooth muscular contortions (called segmentation) before sending partially digested food (chyme) to the small intestines. 

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

Two sphincters keep the contents of the stomach contained. They are the esophageal sphincter (found in the cardiac region, not an anatomical sphincter) dividing the tract above, and the pyloric sphincter dividing the stomach from the small intestine.

The stomach is divided into four sections, beginning at the cardia, each of which has different cells and functions:

• The cardia is where the contents of the esophagus empty into the stomach. The cardia is defined as the region following the "z-line" of the gastroesophageal junction, the point at which the epithelium changes from stratified squamous to columnar. Near the cardia is the lower esophageal sphincter.

• The fundus is formed by the upper curvature of the organ.

• The body is the main, central region.

• The pylorus is the lower section of the organ that facilitates emptying the contents into the small intestine.

The lesser curvature of the stomach is supplied by the right gastric artery inferiorly, and the left gastric artery superiorly, which also supplies the cardiac region. The greater curvature is supplied by the right gastro-omental artery inferiorly and the left gastro-omental artery superiorly. The fundus of the stomach, and also the upper portion of the greater curvature, is supplied by the short gastric artery which arises from the splenic artery.