The main purpose of the stomach is to digest food. It serves as a muscular sac that breaks down food with the aid of stomach acids and enzymes, such as pepsin. This mechanical and chemical breakdown converts food into a semi-liquid substance called chyme, which is then gradually emptied into the small intestine for further digestion and nutrient absorption. The stomach also plays a role in regulating the passage of food into the intestine, secreting substances that aid in digestion, and protecting the body from pathogens present in food.