What is the main role of the liver in digestion?

The main role of the liver in digestion is the secretion of bile. Bile is a digestive fluid that is essential for the emulsification of fats, allowing for their proper digestion and absorption in the small intestine. When food, especially fatty food, enters the small intestine, bile is released from the liver to help break down these fats into smaller, more manageable droplets. This process not only aids in fat digestion but also optimizes the absorption of fat-soluble vitamins and nutrients.

The other options, while important functions related to digestion and overall health, do not represent the primary role of the liver. The absorption of nutrients occurs mainly in the small intestine rather than the liver itself; the liver processes these nutrients after they are absorbed. The mechanical breakdown of food is primarily the role of the teeth and muscular action in the stomach and does not involve the liver at all. Although the liver does store some vitamins, particularly vitamins A, D, E, and K, this function is secondary to its role in bile secretion in the context of digestion.