What are bile and villi? What is their use in the digestive system?

Bile is a substance produced by the liver and stored in the gall bladder—a small organ attached to the liver.

The purpose of bile is to allow digestive enzymes called lipases to be able to hydrolyze or break down fats.  When a meal is eaten, bile stored in the gall bladder is released and enters the small intestine via the bile duct. In the presence of fat molecules, it acts to break up these large molecules into smaller droplets in a process called emulsification.  This allows more surface area for fat enzymes (lipases) to act on aiding in the process of digestion.

Villi are tiny finger-like projections found in the lining of the small intestine. Their purpose is to aid in the absorption of the end products of digestion. These tiny projections greatly increase the surface area for absorption of nutrients into the circulating blood and lymph systems. The villi are one-cell thick, which allows for diffusion to occur. Capillaries within the villi absorb amino acids and monosaccharides while the lacteals inside the villi absorb the end products of fat digestion. Capillaries are tiny blood vessels and lacteals are part of the lymph system. Eventually, all of the end products of digestion are circulated in the body and transported to the cells that need them.

I have included links showing the small intestinal lining and the anatomy of a villus.