The digestive system provides two major functions: digestion, the physical and chemical breakdown of food and absorption, the transfer of nutrients from the digestive tract into the blood or lymphatic circulatory systems. The gastrointestinal tract has several sphincters, which are often named according to their anatomical locations. The digestive tract contains our major tissue layers: the mucosa, submucosa, muscular layer, and serosa. The gastrointestinal tract also communicates with the central nervous system. The mouth is the entry point for food into the digestive tract. The esophagus is long tube that connects the pharynx with the stomach. The small intestine is the primary site of chemical digestion and nutrient absorption. The hypothalamus, a region of the brain, mediates the effect of hunger and appetite and helps regulate satiety. Many of the common digestive disorders, such as heartburn constipation, and irritable bowel syndrome, can be treated with diet changes. These may include increasing fiber intake and avoiding large meals high in fat.