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Human Body
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.catalysts), helps in the digestion of protein and destruction of bacteria. It continues to be produced even when the stomach is empty. Rennin acts on the milk and separates its solid portion. Thereafter, in the presence of the acid, pepsin breaks down the proteins to polypeptides which would be finally digested in the intestine Some form of sugar is absorbed by the blood-vessels from the stomach itself. Mucip lines the stomach and protects it from the acid and prevents it from digesting itself. Gradually the thick gruellike mixture of food and digestive juices called chyme is pushed by vigorous peristaltic waves of the stomach towards the pyloric valve which opens into duodenum, the first part of the small intestine. The function of the pyloric valve is to restrict the admittance of the highly acidic mass into the duodenum-no more than can be instantly neutraJized by alkali arriving from pancreas and liver. Peristalsis is the name given to the slow automatic movement of the stomach and also along the whole length of the gascrointestinal tract, propelling the content onwards. After the stomach has been empty for a long time, intense rhythmic hunger-contractions may sweep over its body. 14. Small Intestine
The stomach extends from the aesophagus to the duodenum, the first portion of the small intestine. The lower end of the stomach which becomes considerably narrower is connected to the small intestine through pyloric valve. The small intestine which is a coiled twisted mass in the centre of the abdomen is divided into three parts : (i) duodenum (adjacent to the stomach), (ii) jejunum and (iii) ileum, totalling more than 7 metres. It is the third processing station of the digestive track. Like the stomach, it mixes and moves the food. It is here that the main work of digestion and about 90% of the absorption of the food constituents into the blood-stream takes place. A variety of enzymes and other digestive substances secreted not only by the small intestine but also by the liver and pancreas, act here and complete the breakdown of proteins, carbobydrates and fats into simple constituents. Here too, the major work of absorption takes place and nutrients are absorbed through the intestinal wall into the blood
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