The stomach is the widest part of the digestive tract, located in the upper left part of the abdomen. It is the part of the digestive system that connects the esophagus to the small intestine. It lies below the diaphragm, in front of the spleen and pancreas, and partially behind the liver. The general anatomy of the stomach can be divided into four parts, which are the cardia, the fundus, the body, and the pyloric region. It is often shaped like a capital J, but its exact shape varies among people and the amount of stomach contents it contains.
The stomach is connected to the esophagus at the esophageal canal, which lies near the heart. For this reason, the region nearby is called the cardia, or the cardiac part. The fundus lies to the left of the cardia and slightly above it, underneath the diaphragm. The region called the body is the largest and lies in the middle of the stomach.
In the anatomy of the stomach, the pyloric part is further divided into the pyloric antrum, canal, and sphincter. This region channels partially digested stomach connects, called chyme, into the small intestine. The pyloric antrum is the widest part of this region, which narrows into the canal. The pyloric sphincter is a round muscle that, when it contracts, directs the passage of chyme into the small intestine.
The outer anatomy of the stomach shows two curving portions. The inward-curving portion on the left is called the lesser curvature. The outward-curving part is known as the greater curvature. The stomach has the ability to expand greatly and may be able to hold up to a gallon (4 liters) in some people. The muscular wall of the stomach works to further break down its contents and expose food surfaces to the secretions that digest food.
One feature of the cellular anatomy of the stomach is a layer of tissue containing goblet cells. These cells produce a mucus lining that protects the stomach from it own secretions, which would otherwise break it down. The goblet cells themselves cannot survive long in the stomach, and are replaced every few days or so.
Special cells that produce the stomach juices are also part of the microscopic anatomy of the stomach. Parietal cells are responsible for producing hydrochloric acid (HCl). The very acidic nature of stomach contents is mostly due to HCl. Another type of cell, called chief cells, secretes an enzyme that helps break down proteins.