Villi are small, finger-like projections that extend into the lumen of the small intestine, increasing its surface area to enhance nutrient absorption. They are approximately 0.5 to 1.6 mm long and covered by epithelial cells with even smaller projections called microvilli, forming a brush border that further increases the absorptive surface. What makes villi well suited for their function includes:

• Large surface area: The finger-like shape and presence of microvilli boost the intestinal surface area by about 40 to 600 times, allowing more efficient absorption of nutrients.
• Thin walls: Each villus is only one cell thick, minimizing the diffusion distance for nutrients to enter blood vessels.
• Rich blood supply: Villi contain networks of blood capillaries that absorb amino acids, sugars, and other nutrients directly into the bloodstream.
• Lymphatic vessels: Each villus has a lacteal (lymph capillary) to absorb and transport fats and fat-soluble vitamins.
• Mobility: Villi can contract and expand to help move absorbed nutrients into the circulatory system.
• Protective cells: Goblet cells in the villi produce mucus to protect the intestinal lining.

These features combined make villi highly efficient at absorbing nutrients from digested food into the body.