The given picture depicts the surface of small intestine. What is the main reason, it so convoluted?
It is to increase the surface area for absorption
The main function of the small intestine is final digestion and absorption. Absorption is directly dependent on the surface area. So to increase the surface area, the internal surface of the intestinal wall is folded onto itself creating villi. Again the surface of each villus is convoluted in a similar fashion and the resulting microscopic structures are called microvilli (brush border).