Anatomy or structure of Stomach :
It is 'J' shaped hallow organ lying in the abdomen under the diaphragm. Its major part is to the left of midline. Its capacity is 1-2 litres. It stores food and partially digest it by gastric juice The stomach is continuous with the oesophagus at the cardiac sphincter and with then duodenum at the pyloric sphincter. It has two curvatures. The lesser curvature is short, lies on the posterior surface of the stomach and is the downward continuation of the posterior wall of the oesophagus.
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| Fig: Different Parts of Stomach |
The stomach is divided into three regions: the fundus, the body and the pylorus. At the distal end of the pylorus is the pyloric sphincter, guarding the opening between the stomach and the duodenum. When the stomach is inactive the pyloric sphincter is relaxed and open, and when the stomach contains food the sphincter is closed.
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| Fig: Walls of Stomach |
Walls of the stomach
The four layers of tissue that comprise the basic structure of the alimentary canal are found in the stomach butwith some modifications.
Muscle layer :
This consists of three layers of smooth muscle fibres: an outer layer of longitudinal fibres, a middle layer of circular fibres and an inner layer of oblique fibres. The stomach is different from other regions of the alimentary tract as it has three layers of muscle instead of two. This arrangement allows for the churning motion characteristic of gastric activity, as well as peristaltic movement.Circular muscle is strongest between the pylorus and the pyloric sphincter.
Mucosa :
When the stomach is empty the mucous membrane lining is thrown into longitudinal folds or rugae, and when full the rugae are 'ironed out' giving the surface a smooth, velvety appearance. Numerous gastric glands are situated below the surface in the mucous membrane and open on to it. They consist of specialised cells that secrete gastric juice into the stomach.
Arterial supply to the stomach is by the left gastric artery, a branch of the coeliac artery, the right gastric artery and the gastroepiploic arteries. Venous drainage is through veins of corresponding names into the portal vein.
Functions of stomach :
1. Mechanical functions :
It act as a reservoir of food. It helps in mixing of food with digestive juices. It liquefies and propels the food further into duodenum.
2. Secretion :
It secretes gastric juice which converts food into chime and helps in digestion.
3. Antiseptic :
Hydrochloric acid of gastric juice destroys microbes and prevents infection.
4. Digestion :
Gastric juice partly digest proteins and fats
5. Absorption :
Water, glucose, alcohol and certain drug are absorbed from wall of stomach.
6. Excretion :
It helps in excretion of some toxins and drugs.
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