Why does absorption of digested good occur mainly in the small intestine?

Asked by devansh verma | 3rd Jun, 2012, 06:23: PM

Expert Answer:

Since small intestine is adapted to carry out absorption of food in following ways:
  • Most absorption takes place by diffusion, so the rate of absorption is determined by the surface area available and the concentration gradient across the cell membrane. The intestine is specialized to maximize both.

 

  • The walls of the intestinal lumen are folded into convoluted wrinkles which increase its surface area. The epithelial layer is then folded into tiny finger-like extensions called villi. Villi increase the internal surface area of the intestinal walls. Increased surface area allows for increased intestinal wall area that is available for absorption. Villi are specialised for absorption in the small intestine as they have a thin wall, about one cell thick, which enables a shorter diffusion path. The membrane of each epithelial cell that faces the lumen is then folded again into tiny cellular extensions called microvilli. They also contribute in increasing the surface area. 

 

  • The villi is connected to the blood vessels so the circulating blood then carries these nutrients away. The constant flow of blood through the capillaries of the villus ensures that blood rich in nutrients is always being removed and replaced with blood low in nutrients, thus the high concentration gradient between the lumen and the epithelial cells is maintained.

Answered by  | 4th Jun, 2012, 11:33: AM

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