Describe how the small intestine is adapted for efficient glucose absorption. (3 marks)

The small intestine has a very large surface area to increase the amount of area that glucose can diffuse out of the small intestine into the bloodstream. The large surface area is created by villi, which are thousands of small, finger-like projections on the inside surface of the small intestine. Each one is only one cell thick, which means the area over which the glucose has to diffuse is very thin, so it can happen more quickly. The villi also each have a network of capillaries surrounding them so the glucose is quickly taken away once it diffuses out of the small intestine. This helps to maintain a steep concentration gradient of glucose between the small intestine and the blood around it, so diffusion happens more quickly.