Question

How is the structure of a villi in the small intestine related to its functions?

Answer 1

Digestion of all digestible components of food is completed in the small intestine. Small intestine is the longest part of the alimentary canal which measures anything between 4.5 to 7 m in length. The small intestine has the narrowest diameter that’s why it is named so. It is coiled in the abdomen.

Complete answer:
Internally, the small intestine possesses two types of ingrowths, circular folds and villi. Circular folds are also called plicae circulares (valves of Kerchkring/Kerckring or valvulae conniventes). They slow down the movement of food through the intestine as a result foods remain for longer time in the intestine.
Major seat of digestion of food is the small intestine . For this, it has villi which increases its absorptive surface by 10 times. Villi are small prolongations of the intestinal lining. Each villus has a large lymph vessel called central lacteal, some fine lymph vessels and a number of blood capillaries. Cells lining the villi have numerous microvilli on the free surface. They are specialised for absorption of food. At the bases of villi are present glandular areas called crypts of Lieberkuhn.
The villus epithelial cells have tight junctions which prevent the loss of nutrients. They also have many mitochondria, producing ATP for active transport across the phospholipid bilayer from the lumen of the intestine.
From villus, project microscopic cells called microvilli, which further increases surface area for faster absorption. Microvilli have protein pumps that move monosaccharides and amino acids into the bloodstream and also contain mitochondria so that large amounts of DNA can be made for active transport of nutrients.

Note:
Villi are largest and most numerous in the Jejunum and duodenum and become fewer and smaller in the ileum. The essential parts of a villus are the lacteal vessel, the blood vessels, the epithelium, the basement membrane, and the muscular tissue of the mucosa, all being supported and held together by retiform lymphoid tissue.