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Body Talk

Stomach: The flexible pear-shaped organ

What do you do when you are hungry and the stomach starts rumbling? Eat some food of course. But there are times that we eat a little too much, and then end up feeling all stuffed up ... So, food plays a vital role when it comes to our survival, and the stomach plays a key role when it comes to the food we eat ... Let's check out what the stomach is like.

The stomach is one of our least mysterious organs: we all think we know what it does.

But did you realise how intricately designed and complicated it is? And did you know that the stomach isn't, as most people think, in the middle behind the navel? In fact, it's higher up in the abdomen, under the bottom of your rib cage in the middle and behind the lower ribs on the left side.

The stomach is no passive food bag that just stores, warms and softens food and drink. It is able to expand and contract in response to how much it contains, converts solids into fluid to promote digestion, squeezes food towards its exit and then forces it through rhythmically, into the next part of the intestine.

In addition, due to its links with many of the body's other systems, including the brain, hormones and the nervous system, the stomach can be affected by your feelings, just as much as, by what you eat.

The stomach is a flexible pear-shaped organ which, when full, is not unlike a boxing glove in size and form. It is about 30 centimetres (12 inches) around and 10-25 centimetres (4-10 inches) across.

Average capacity is about 1.5 litres (2.6 pints). The stomach hangs freely suspended and changes its position and shape depending on the amount of food it contains.

At its top end, the stomach is connected to the oesophagus, the tube which conveys food and drink from the throat. Food enters the stomach at a part known as the fundus. At its lower end, the stomach is connected to the duodenum, the first part of the small intestine. The whole journey is seven metres (23 feet) long, and food takes 24 hours on average to pass through the digestive system.

Around the stomach is a thick coat of muscles - lengthwise on the outside, circular in the middle, diagonal on the innermost layer. A muscle at the lower end of the stomach forms a ring, the pyloric sphincter, that can close the outlet to the duodenum.

The breakdown and absorption of food involves the bloodstream, the nervous system, hormones and enzymes, all working together. The nervous system controls many of the stomach's actions. Enzymes in the stomach act like chemical knives to assist food breakdown. Hormones help to regulate digestion and the bloodstream carries nutrients around the body.

The stomach wall, or lining, consists of cells supplied by blood vessels and nerves, and contains 35 million glands. Every day, these secrete two to three litres of gastric juices to aid digestion, and mucus to prevent the stomach from digesting itself.

Why is this network so complex? It's because the constituents (parts that make up) of food are themselves so complex. Proteins, carbohydrates and fats couldn't be transported into the blood stream, absorbed by the body's cells and used properly unless they are thoroughly broken down - that is, digested.

We all know that digestion begins in the mouth. The stomach's main job is to continue this 'softening up' before food passes, bit by bit, into the small intestine, where the main digestive process takes place.

How does the stomach digest food? That's where the stomach's digestive juices come in:

* Gastrin causes the stomach to produce acid which starts to digest foods through the breakdown of proteins. Gastrin is also needed for the normal growth of the stomach's lining.

* Pepsin, which breaks down proteins found in meat, cheese and beans.

* Hydrochloric acid, which kills bacteria and provides the best environment for the pepsin to work well.

* Intrinsic factor, essential for the absorption of vitamin B12. A lack of vitamin B12 causes anaemia.

* Mucus which protects the cells lining the stomach from the harsh acid environment of the stomach.

* Gastric lipase which helps digest fat.

The stomach's work takes place in three phases. First, the gastric motor is turned on. The anticipation, sight and smell of food trigger the brain to alert the stomach to prepare for food. This stimulation induces the secretion of gastrin and small amounts of acid.

Next, the gastric motor is up and running. Food's arrival in the stomach stimulates the release of gastrin. The muscles around the stomach adjust their size according to the amount of food the stomach contains, and produce rhythmic contractions about every 20 seconds.

These contractions, together known as peristalsis, knead, toss and churn the food, mixing it with gastric juices to convert it into a creamy fluid called chyme. If the stomach is empty, these contractions are felt as hunger pangs. In addition, pepsin is formed and more acid is secreted.

Finally, the stomach empties through the pyloric sphincter, a purse-string muscle. Chyme is squirted in small amounts into the duodenum. Gradually, the nervous system and hormones together apply the gastric motor's brakes.

What can go wrong with the stomach...

Dyspepsia - almost everyone has tummy upsets from time to time. Probably the most common is indigestion, or dyspepsia. Dyspepsia is a pain or burning sensation in the lower chest or upper abdomen that is usually related to eating and drinking. This can be made worse by: eating too much or too fast, spicy or fatty foods, tension, anxiety or emotional upsets, tight clothing, certain medicines, too much coffee and chocolate.

Gastroenteritis - inflammation of the lining of the stomach and intestines - is the most common cause of vomiting and diarrhoea. It is caused by viruses and bacteria that are responsible for food poisoning or traveller's diarrhoea.

Gastritis - an inflammation of the stomach lining that has been caused by consuming too many foods that irritate the stomach.

Compiled by Chamitha

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