Structure of the stomach
The stomach lies in the upper abdominal cavity, just below the diaphragm. It is continuous with the oesophagus at the cardiac sphincter and the duodenum at the pyloric sphincter. It is divided into three regions: the fundus, body and the antrum. The walls of the stomach are made up of muscle layer (longitudinal, circular and oblique muscle), submucosa and mucosa.
Functions of the stomach
- Temporary storage allowing time for digestive enzymes to act
- Chemical digestion
- Mechanical breakdown and production of chyme
- Limited absorption of water, alcohol and some fat-soluble drugs
- Non-specific defense against microbes
- Preparation of ion for digestion further along the tract
- Production of intrinsic factor needed for absorption of vitamin B12 in the terminal ileum
- Regulation of the passage of gastric contents into the duodenum
Secretion and functions of gastric juice
There is always a small amount of gastric juices in the stomach, even when it contains no food. Secretion reaches its maximum level about one hour after a meal.
About two litres of gastric juices are secreted daily by glands in the mucosa. Gastric juice consists of:
- Water and mineral salts, secreted by gastric glands
- Mucus secreted by goblet cells in the glands and on the stomach surface
- Hydrochloric acid and intrinsic factor, secreted by parietal cells in the gastric glands
- Inactive enzyme precursors
- The water further liquefies the food swallowed.
- The hydrochloric acid:
- acidifies the food and stops the action of enzymes from saliva;
- kills ingested microbes;
- provides the acid environment required for effective digestion by pepsin.
- The mucus prevents accidental injury to the stomach by lubricating the contents, and prevents chemical injury by acting as a barrier to the corrosive gastric juice.