Ironically, the longest part of the alimentary canal is the small intestine. It is a highly coiled structure of about 7.5 meters in length. It is a very narrow tube with a large internal surface area. It is the site of complete digestion in humans. It absorbs digested food completely. It secretes intestinal juice. It receives bile juice from the liver and pancreatic juice from the pancreas.
The small intestine is divided into three parts:
- Duodenum
- Jejunum
- Ileum
Functions of Small Intestine
Complete Digestion of Food
- The partially digested food is absorbed by the duodenum of the small intestine along with the digestive juices from the liver, pancreas and its own walls.
- The liver secretes the bile juice, which converts fat into tiny droplets so that their digestion becomes easy.
- The pancreas produces pancreatic juice that breaks down fats into fatty acids and glycerol.
- The intestinal juice secreted by the walls of the small intestine breaks down starch and carbohydrates into simple sugars. These sugars are known as glucose. It also converts the proteins into amino acids.
- All these simple, broken down forms are called the digested food.
Absorption of Digested Food
The food that is digested is absorbed into the blood vessels in the walls of the intestine.
The finger-like projections known as villi, drastically increase the surface area of the small intestine for greater absorption of the digested food.
The blood carries the absorbed food material to different parts of the body. Glucose breaks down to form oxygen and carbon dioxide and releases the energy required for various life processes.
The undigested and unabsorbed food passes from the small intestine to the large intestine.
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