Web hosting Custom Email SiteBuilder

Stomach

The stomach is a hollow, sac-like organ connected to the oesophagus and the duodenum (the first part of the small intestine), consists of layers of muscle and nerves that continue the breakdown of food which begins in the mouth. It is also a storage compartment, which enables us to eat only two or three meals a day. If this weren't possible, we would have to eat about every twenty minutes.

The average adult stomach stretches to hold from two to three pints and produces approximately the same amount of gastric juices every twenty-four hours.

The stomach has several functions:

• as a storage bin, holding a meal in the upper portion and releasing it a little at a time into the lower portion for processing
• as a food mixer, the strong muscles contract and mash the food into a sticky, slushy mass known as chyme
• as a sterilising system, the cells in the stomach produce hydrochloric acid which kills invading organisms and neutralises many toxins
• as a digestive tub, the stomach produces digestive fluid which splits and cracks the chemicals in food to be distributed as fuel for the body.

This picture shows an X ray of the stomach of a patient who has swallowed a barium meal. 

The stomach is marked St

On the whole the stomach does not play much part in absorption but it is possible for a small amount of water to be absorbed. In addition around 20% of any alcohol intake is absorbed into the stomach and also some drugs are directly absorbed here (most noticeably acetylsalicylic acid [aspirin]).

The process of digestion is triggered by the sight, the smell or the taste of food. Thus the stomach is prepared when the food arrives. Every time you pass a bakery shop or smell good cooking, the body begins a digestive process. If the stomach is not filled, these gastric juices begin eroding the stomach lining itself and hence we get gastric or peptic ulcers.

The pyloric region is at the top of the stomach and narrows to become the "pyloric canal" as it approaches the junction with the small intestine. At the end of the pyloric canal, the circular layer of fibres in its muscular wall is thickened, forming a powerful muscle called the "pyloric sphincter." This muscle serves as a valve that prevents regurgitation of food from the intestine back into the stomach.

Helicobacter pylori is a spiral shaped bacterium that lives in the stomach and duodenum (section of intestine just below stomach). It has a unique way of adapting in the harsh environment of the stomach.

The inside of the stomach is bathed in about half a gallon of gastric juice every day.

Gastric juice is composed of digestive enzymes and concentrated hydrochloric acid, which can readily tear apart the toughest food or micro-organism. Bacteria, viruses, and yesterdays steak dinner are all consumed in this deadly bath of chemicals. It used to be thought that the stomach contained no bacteria and was actually sterile, but Helicobacter pylori changed that.

The stomach is protected from its own gastric juice by a thick layer of mucous that covers the stomach lining. Helicobacter pylori takes advantage of this protection by living in the mucous lining.

Once H. pylori is safely ensconced in the mucous, it is able to fight the stomach acid that does reach it with an enzyme it possesses called urease. Urease converts urea, of which there is an abundant supply in the stomach (from saliva and gastric juices), into bicarbonate and ammonia, which are strong bases. This creates a cloud of acid neutralising chemicals around the H. pylori, protecting it from the acid in the stomach.

This reaction is important for diagnosis of H.pylori by breath testing.

It may not be H. pylori itself which causes peptic ulcer, but the inflammation of the stomach lining; i.e. the response to H. pylori by the body's immune system.

The picture above shows a photomicrograph of the stomach lining inhabited by H.pylori. The bacteria are the black squiggly things arrowed.

This page last updated Friday, 30 April 1999 10:44 +0100