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Your amazing bodyStomachThe stomach is one of our least mysterious organs: everyone thinks they know what it does. But did you realise how intricately designed and complicated it is? For example, it is only thanks to a protective lining of jelly-like mucus that stops the corrosive hydrochloric acid in the stomach burning through the stomach wall. 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 squirts it 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.
How the stomach is constructedThe 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 7 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 involve the bloodstream, the nervous system, hormones and enzymes, all working together.
The stomach wall, or lining, consists of cells supplied by blood vessels and nerves, and contains 35 million glands. Every day, these secrete 2-3 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 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.
What the stomach doesDigestion 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 take place. How does the stomach digest food? That's where the stomach's digestive juices come in:
The stomach's work takes place in three phases. First, the gastric motor is turned on and begins to idle. 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 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 stomachDyspepsia - 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:
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, for example alcohol. Peptic ulcers - inflamed breaks in the lining of the duodenum (duodenal ulcers) or stomach (gastric ulcers) are the most common serious stomach disorder. Factors associated with peptic ulcers include:
Pernicious anaemia - can develop when the stomach fails to produce intrinsic factor, which is needed to absorb vitamin B12. This leads to anaemia, causing headaches, tiredness and lethargy, and dizziness. Stomach cancer - also known as gastric cancer, is a malignant tumour that grows from the lining of the stomach. You should tell your doctor about any new symptoms of pain, weight loss or indigestion, especially in later life. Hiatus hernia - a protrusion of the stomach into the chest, is associated with conditions that increase pressure in the abdomen, such as excess weight or a persistent cough caused by smoking. Most hiatus hernias have no symptoms but they can cause heartburn (nothing to do with heart but a burning sensation when stomach acid flows back into the oesophagus) or chest pain, especially after eating or on bending over or lying down. How to maintain a healthy stomachBeing aware of your lifestyle can minimise the risk of stomach problems.
As with many conditions, the surest course is to be kind to yourself - treat and maintain your body sensibly and with respect because your body is, by and large, amazingly self-sustaining. - - - - - - - - - April 2002 Back to the'Your amazing body' index. |
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