What is the function of ileum?

Absorption:

- Water absorption: The ileum actively absorbs water from the chyme, further concentrating the digestive contents. Through active transport, sodium ions get absorbed via the Na+/K+ ATPase pump found on the mucosal epithelium, and water follows passively to maintain osmotic balance, reducing the chyme's volume.

- Electrolyte absorption: Along with water, electrolytes like sodium, potassium, chloride, and bicarbonate ions are also absorbed from the chyme. The absorption of electrolytes is coupled with various transport processes, including active transport and ion exchange mechanisms, ensuring proper electrolyte balance in the body.

- Bile salt absorption: The ileum plays a crucial role in reabsorbing bile salts, which aid in fat digestion. Specialized epithelial cells in the ileum actively take up bile salts from the chyme against a concentration gradient, allowing their reuse in the process of fat digestion and absorption.

- Vitamin absorption: The terminal portion of the ileum is responsible for the absorption of vitamin B12 (cobalamin). This essential vitamin requires a specific protein called intrinsic factor for absorption, which is produced by the stomach. Vitamin B12 binds to intrinsic factor and is absorbed into the bloodstream in the ileum.

Mucosal Immunity:

- Gut-associated lymphoid tissues: Peyer's patches and gut-associated lymphoid tissues (GALT) are abundant in the ileum, contributing to the mucosal immune system. They contain immune cells that help protect against antigens present in the digestive contents and play a role in immune tolerance, preventing reactions against harmless substances in food.

By combining these functions, the ileum plays a crucial role in completing the process of digestion and nutrient absorption, ensuring optimal nutrient utilization and protecting against harmful substances in the gastrointestinal tract.