Which part of the digestive system is the main site for nutrient absorption?

The small intestine is the primary site for nutrient absorption in the digestive system. It is composed of three segments: the duodenum, jejunum, and ileum, each playing a vital role in the absorption process. The inner walls of the small intestine are lined with tiny, finger-like projections called villi, which significantly increase the surface area for absorption. These villi are covered with microvilli, forming a brush border that further enhances the absorption capacity by creating a vast surface area that can efficiently take up nutrients.

As food is digested in the small intestine, carbohydrates, proteins, and fats are broken down into their smaller components—simple sugars, amino acids, and fatty acids—allowing these nutrients to pass through the intestinal walls into the bloodstream. This absorbed nutrient-rich blood is then transported to the liver and other parts of the body where these nutrients can be utilized for energy, growth, and repair.

The other parts mentioned in the options have different roles in the digestive process. The stomach's primary function is to break down food through mechanical and chemical means but not to absorb significant amounts of nutrients. The mouth initiates the digestive process by mechanically breaking down food and mixing it with saliva, but actual nutrient absorption does not occur here.