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The stomach

The stomach is part of the digestive system. It lies just under the diaphragm (the muscular sheet just under your lungs). The top of the stomach is connected to the oesophagus (food pipe). The other end of the stomach is connected to the first part of the small bowel, the duodenum.

What does the stomach do?

The stomach is a muscular bag. Its main job is to mix up the food that is eaten and start breaking it down so that it can be easily digested.

Digesting proteins

The lining of the stomach contains glands, which make and release the stomach juices. These juices contain an acid and a digestive enzyme called pepsin. Pepsin starts to break down (digest) proteins in the food so that the body can absorb them. The acid is necessary for pepsin to work properly. It also helps to kill bacteria that might be in the food.

Vitamin B12

The stomach also makes another chemical that is needed for the body to absorb vitamin B12. This vitamin is needed by the body to help in the making of red blood cells and to keep the nervous system healthy.

 

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The parts of the stomach

The stomach is part of the digestive system. It lies just under the diaphragm (the sheet of muscle just under your lungs). The top of the stomach is connected to the oesophagus (foodpipe). The other end of the stomach is connected to the first part of the small bowel, the duodenum.

Diagram showing the parts of the stomach

The stomach has three main parts. The top is called the fundus. The middle is called the body of the stomach. The bottom is called the antrum or pylorus. There is a valve called a sphincter at each end of the stomach. The valve between the oesophagus and the top of the stomach is called the cardiac sphincter. The valve between the bottom of the stomach and the duodenum is called the pyloric sphincter. The stomach does several different jobs.

 

How the stomach mixes and breaks down food

The stomach is a muscular bag. Its main job is to mix up the food that is eaten and start breaking it down so that it can be easily digested. When food enters the stomach, the muscles of the stomach wall begin powerful contractions, which pass over the stomach in waves. These muscle contractions mix up the food and break it down until it is a thick liquid. This makes digestion in the duodenum easier.

 

Beginning the digestion of proteins

The lining of the stomach contains glands, which make and release (secrete) the stomach juices. The stomach juices contain an acid and a digestive enzyme called pepsin. These begin to flow as soon as we see or smell food, well before food even enters the stomach. The enzyme starts to break down (digest) proteins in the food so that the body can absorb them. The acid is needed for the enzyme to work properly. It also helps to kill bacteria that might be in the food and so helps to protect against food poisoning.

There are other glands in the stomach lining that make thick mucus. This mucus helps to protect the stomach lining from being damaged by the acid and protein digesting enzyme in the stomach juices.

 

Helping to absorb vitamin B12

The stomach makes another chemical that is needed for the body to absorb a vitamin called vitamin B12. This vitamin is needed by the body to help make red blood cells and to keep the nervous system healthy.

 

Where food goes after the stomach

After about two hours in the stomach, the semi liquid, partly digested food moves into the duodenum, where it continues to be digested. The digested food then moves through the small intestine (small bowel) where the digested nutrients are absorbed into the body. The waste that is left behind then moves through to the large bowel. In the first part of the large bowel (colon) water is absorbed so that the waste matter begins to solidify into poo (faeces or stool).

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Updated: 11 February 2014