What is the main function of the small intestine?

The primary function of the small intestine is the absorption of nutrients. As food is digested, it travels from the stomach into the small intestine, where the majority of nutrient absorption occurs. The small intestine is lined with tiny hair-like structures called villi, which increase the surface area for absorption significantly. This allows the body to effectively absorb essential nutrients, vitamins, and minerals from the food consumed, providing energy and supporting overall bodily functions.

The other options present functions that are characteristic of different organs or systems in the body. The storage of bile is primarily a function of the gallbladder, which stores bile produced by the liver for digestion. Production of insulin occurs in the pancreas, an organ that plays a critical role in glucose metabolism and blood sugar regulation. Filtration of blood is mainly carried out by the kidneys, which remove waste products and excess substances from the bloodstream to maintain homeostasis.