Explain how the structure of a villus helps absorption of the products of digestion in the small intestine.
The inside wall of the small intestine is folded which increases the surface area. When we look at the surface of the small intestine, we see finger-like projection called villi, and each villi has its own blood supply.
We can see that in a villi there are blood vessels that bring blood supply in and blood supply out. The villi is surrounded by glucose, amino acids, glycerol, fatty acids and in the space around the villi these molecules are in high concentration. The villi increases the surface area for absorption. Villi also has a small diffusion distance meaning that the diffusion happens fast. The blood vessel's distant is also quite close to the space outside meaning the molecules can diffuse in the bloodstream fast. Because the blood is flowing in and out, the blood supply out removes the molecules which are diffused into the blood and this maintains the concentration gradient by keeping the concentration in the blood low which is maintained by the blood flow.
The small intestine helps with the absorption of the lipid, and the lacteal collect the lipids before it is returned to the circulatory system.