how does intestine provides a place for easy absorption?explain briefly as points
- 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. Increased absorptive area decreases the average distance traveled by nutrient molecules, so effectiveness of diffusion increases. 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.
- 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. They have a large surface area so there will be more efficient absorption of fatty acids and glycerol into the blood stream. They have a rich blood supply to keep a concentration gradient. Villi also help the intestines to move food along the digestive pathway.