Stomach

What is the Stomach?

The stomach is the storage organ of the body. It is a dilated portion of the alimentary system. It is a strong hollow sac beginning, where the esophagus ends and ending in the small intestine. When fully stretched the stomach can measure 25 cm. and can hold 1.5 litres of food.

Where is the stomach situated?
The stomach is situated in the upper part of the abdomen, extending from below the left ribs into the region below the breastbone, reaching up to the navel. The abdominal muscles, the left lung and a part of liver cover the stomach from the front. Behind the stomach is placed the diaphragm, left kidney, spleen, pancreas and a part of the large intestine.

How can we describe the stomach?
The stomach is roughly J shaped and has two openings. The point where the esophagus ends into the stomach is called as the cardiac orifice or the lower esophageal sphincter. The point where the stomach gives way to the small intestine is called as the pyloric orifice.

The stomach itself can be divided into:

• The fundus : This is the dome shaped projection of the stomach upwards and to the left of the cardiac orifice. The fundus usually contains gas produced by digestion of food in the stomach.
• The body : It extends from the cardiac orifice to the pylorus. It contains a lot of acid secreting cells called gastric cells.
• The pylorus : It is the most tubular part of the stomach that ends in the pyloric sphincter, which is a thickening of the muscular layers of the stomach. The pylorus opens into that part of the small intestine called the duodenum.

The stomach is lined by various coats. The innermost coat is the mucus membrane. It is thick and many blood vessels traverse through it. It is thrown into numerous folds called rugae or gastric pits, which increase the surface area of the stomach. The gastric glands, which secrete acid, are present in the folds of the rugae. The muscular layer is placed next consisting of lengthwise-arranged muscle fibres and circular muscle fibres.

Functions of the Stomach

1. The stomach functions as a storage system for food. The bolus arriving from the esophagus enters the stomach through the pyloric sphincter. The food is then churned in the stomach, thus mixing it with the acids thoroughly. The food is then converted to a semi solid state called chyme. The chyme is held in the stomach by the pyloric sphincter until the churning process is complete.
2. The stomach contains acid at a pH of as low as 1.5. This helps in the digestion of food. The stomach also contains various enzymes, which help indigestion.
3. A low blood sugar level and other hormonal factors bring about the feeling of hunger. This gives rise to hunger contractions if the stomach has been empty for a long time.
4. The stomach also regulates the rate of emptying its contents, namely chyme into the small intestine so that it is suitably digested and absorbed by the small intestine.