The small intestine is specially designed to absorb digested food efficiently through several key structural features:
- Villi and Microvilli: The inner surface of the small intestine is covered with millions of tiny finger-like projections called villi. Each villus is further covered with even smaller projections called microvilli. This dramatically increases the surface area available for absorption, allowing for a greater amount of digested food to be absorbed at one time.
- Surface Area: The massive increase in surface area due to villi and microvilli maximizes the rate and efficiency of absorption by providing more area for nutrient molecules to pass through the intestinal walls.
- Rich Blood Supply: Each villus contains a network of blood capillaries that absorb digested nutrients such as glucose, amino acids, fatty acids, and glycerol, then transport them into the bloodstream to be distributed throughout the body.
- Lacteals: Inside each villus, there is a lymphatic vessel called a lacteal which absorbs fats and fat-soluble vitamins and eventually transports them into the bloodstream.
- Specialized Epithelium: The lining of the small intestine is made up of a simple columnar epithelium with absorptive cells called enterocytes, which help facilitate the absorption of nutrients.
- Intestinal Juices: The walls of the small intestine secrete intestinal juices that facilitate the final stages of digestion, breaking down complex food molecules into simpler, absorbable forms.
These features together ensure the small intestine is highly efficient in absorbing nutrients from digested food, making it the primary site of nutrient absorption in the digestive system.
