What substance is secreted into the small intestines for digestion?

Bile is a digestive fluid secreted by the liver and stored in the gallbladder. When food enters the small intestine, bile is released into this organ to aid in the digestion of fats. It contains bile salts that emulsify fats, making them easier for digestive enzymes to break down. This process is crucial for the absorption of fat-soluble vitamins and nutrients in the small intestine.

In contrast, while insulin plays a significant role in regulating blood sugar levels, it does not participate directly in the digestion of food within the intestines. Gastric acid is secreted in the stomach, not the small intestine, and its primary function is to aid in the digestion of food within the stomach itself. Salivary enzymes, such as amylase, initiate the digestion of carbohydrates in the mouth and do not act in the small intestine. Thus, bile is the essential substance secreted into the small intestines specifically for digestion.