Small intestine: It is the longest part of alimentary canal which measures between 4.5 to 7 m in length. The term small intestine is used because this part of the alimentary canal has narrowest diameter. Small intestine lies coiled in the abdomen. Small intestine has 3 parts: Duodenum, jejunum and ileum.
Functions of Small Intestine:
- Small intestine is the major seat of absorption of digested food. For this, it has villi for increasing its absorptive surface by 10 times.
- Digestion of all digestible components of food is completed.
- It produces a number of hormones for controlling the secretary and absorptive activity of different parts. The important hormones are secretin, cholecystokinin, villikinin, enterogasterone, motlin, enterocrinini and duocrinin.
Large Intestine: It is the hindermost part of alimentary canal which opens to the outside through the anus. The larger intestine is called large because it has a wider diameter(4-6 cm) as compared to small intestine (3.5-4.5 cm). The length of large intestine is about 1.5 m. It has 4 regions: caecum, colon, rectum and anal canal.Functions of Large Intestine:
- Absorption of water, so as to convert the liquefied indigestible matter into faecal matter.
- Toxic metals and other toxins are secreted into the faecal matter in the region of large intestine.
- It stores faecal matter temporarily.
- It harbours symbiotic bacteria. The bacteria produce vitamins K, thiamine, riboflavin and B12.
- Its lining layer has mucous glands for lubrication of the solidified faecal matter.