What is the primary function of the ileum in the small intestine?

The ileum, which is the final segment of the small intestine, plays a crucial role in digestion and absorption. Its primary function is to absorb nutrients from the digested food that has passed through the earlier sections of the small intestine (the duodenum and jejunum). The ileum is specifically adapted for the absorption of nutrients such as vitamins, minerals, and particularly vitamin B12, as well as bile salts, which are necessary for the digestion of fats.

Additionally, after the ileum completes its absorption tasks, it facilitates the transition of the remaining material into the large intestine. This function is essential for maintaining proper digestive health, as it ensures that the body efficiently extracts and utilizes the nutrients it needs while appropriately passing waste material to the next stage of the digestive process.

The other options do not accurately describe the role of the ileum. Secretion of bile is primarily the function of the liver and gallbladder, regulation of stomach acidity is managed by the stomach and glands therein, and the breakdown of complex carbohydrates mainly occurs in the mouth and earlier portions of the small intestine with the help of enzymes. All these indicate that the primary role of the ileum is centered on absorption and preparing materials for the transition to the large intestine.