The stomach lies just below the diaphragm in the upper part of the abdominal cavity primarily to the left of the midline under a portion of the liver. The main divisions of the stomach are the following:
The cardia is the portion of the stomach surrounding the cardioesophageal junction, or cardiac orifice (the opening of the esophagus into the stomach). Tumors of the cardioesophageal junction are usually coded to the stomach.
The fundus is the enlarged portion to the left and above the cardiac orifice.
The body, or corpus, is the central part of the stomach.
The pyloric antrum is the lower or distal portion above the duodenum. The opening between the stomach and the small intestine is the pylorus, and the very powerful sphincter, which regulates the passage of chyme into the duodenum, is called the pyloric sphincter.
The stomach is suspended from the abdominal wall by the lesser omentum. The greater omentum attaches the stomach to the transverse colon, spleen and diaphragm.
The common mesentery suspends the small intestine. The parietal peritoneum lies over the duodenum and other structures, such as the abdominal aorta. Because they lie behind the peritoneum, they are called retroperitoneal structures.
Layers of the stomach wall
The stomach is made up of several layers of tissue:
- The mucosa (mucous membrane) is the inner lining of the stomach. When the stomach is empty the mucosa has a ridged appearance. These ridges (rugae) flatten out as the stomach fills with food.
- The next layer that covers the mucosa is the submucosa. It is made up of connective tissue that contains larger blood and lymph vessels, nerve cells and fibres.
- The muscularis propria (or muscularis externa) is the next layer that covers the submucosa. It is the main muscle of the stomach and is made up of 3 layers of muscle.
- The serosa is the fibrous membrane that covers the outside of the stomach. The serosa of the stomach is also called the visceral peritoneum.
The stomach has 3 main functions:
- temporary storage for food, which passes from the esophagus to the stomach where it is held for 2 hours or longer
- mixing and breakdown of food by contraction and relaxation of the muscle layers in the stomach
- digestion of food
The mucosa contains specialized cells and glands that produce hydrochloric acid and digestive enzymes to help digest food. The mucosa in the cardiac and pyloric regions of the stomach release mucus that helps protect the lining of the stomach from the acid produced for digestion. Other specialized cells in the mucosa of the pylorus release the hormone gastrin into the blood. Gastrin helps to stimulate the release of acid and enzymes from the mucosa. Gastrin also helps the muscles of the stomach to start contracting.
Food is broken down into a thick, acidic, soupy mixture called chyme. The pyloric sphincter relaxes once chyme formation is complete. Chyme then passes into the duodenum. The duodenum plays a big role in absorption of the food we eat. The stomach does not play a big role in absorption of food. It only absorbs water, alcohol and some drugs.