Short notes on the structure and function of stomach
The dilated portion of the alimentary canal situated between the oesophagus and the beginning of the small intestine is called the stomach. It is a muscular distensible organ and its shape and size varies. It is about 30 cms long and 15 cms wide. There are four regions in the stomach. These are the cardiac region, fundus, body and the pyloric region. The cardiac region is situated at the upper end of the stomach. The oesophagus opens into this. This opening is called the cardiac orifice.
This is guarded by the cardiac sphincter muscles which prevent the regurgitation (moving back) of the food into the oesophagus. The fundus is the dome like upper part of the stomach and it projects above the cardiac orifice.
The main part of the stomach is called the body and at its lower ends it narrows into the pyloric region. The pyloric region connects itself to the small intestine through the pyloric aparture and is guarded by a valve called the pyloric sphincter. This regulates the movement of the food into the intestine.
Structurally the wall of the stomach is made up of four layers of tissue. These are
1. An outer covering of the serous membrane (the peritoneum)
2. A muscle layer which inturn is made up of three layers of visceral muscle fibres namely longitudinal, circular and oblique.
3. A sub mucous layer consisting of loose areolar tissue carrying blood vessels, lymphatics and nerves.
4. The mucous membrane constituting the inner most layers is thick and smooth having a velvety surface when the stomach is full. When the stomach is empty the mucous membrane is thrown into a number of irregular folds or rugae. These folds open up at the entry of the food and allow the stomach to expand to accommodate a large quantity of food.
The mucous membrane of the stomach contains a number of minute depressions called gastric pits. Embedded in these gastric pits are found a number of glands which secret the gastric juice. There are three types of gastric glands. These are
1. The peptic cells that produce zymogen
2. The oxyntic cells that secret HCL and
3. Mucous cells which add mucous.
The three secretions together form an acidic gastric juice with a pH of 2. The gastric juice is discharged into the stomach. It contains water, salts, mucin, hydrochloric acid, pepsin, rennin and gastric lipase. It has been estimated that on an average about two to three litres of gastric juice is secreted per day.