Food enters stomach through oesophagus. The stomach is present on the left side of abdomen. The food is churned in stomach for nearly three hours. The food breaks into small pieces and converts into semi-solid paste. The wall of stomach contains three tubular glands which secrete gastric juice. The gastric juice contains dilute hydrochloric acid, enzyme pepsinogen and mucus. The mucus protects the stomach wall from its own secretion of hydrochloric acid and pepsinogen. The hydrochloric acid makes the acidic medium in stomach. It also kills the bacteria that has entered along with food. In acidic medium, pepsinogen digests the protein present in the food and converts into small molecules. Thus the digestion of protein begins in the stomach. The partly digested good goes into the small intestine. The exit of food from stomach is regulated by sphincter muscles. The small intestine is the site if complete digestion of carbohydrates, proteins and fats. Small intestine receives secretion from liver and pancreas. Liver secrets bile, which is a greenish yellow liquid and normally stored in the fall bladder. The bile is alkaline in nature and contains salts. It makes the acidic food alkaline so that pancreatic juices can act on it. The bile salts break the fats present in food into small globules. The pancreatic juices secreted by pancreas contain enzymes like amylase, trypsin and lipase. Amylase digests starch, trypsin digests proteins and lipase fats. The glands of the wall of small intestine secrete intestinal juices. Intestinal juices contain various enzymes which complete the digestion of carbohydrates into glucose, proteins into amino acids and fats into fatty acids and glycerol. The inner wall of small intestine has millions of fnger like projections called villi which increase the surface area of the small intestine. This helps in rapid absorption of digested food. The absorbed food passes through the wall of small intestine and goes into blood. The blood carries digested food to all the parts if body where it is assimilated as part of the cells and is utilized for energy, growth and repair. The undigested food travels from small intestine to large intestine.