Fats, carbohydrates, and proteins are broken down to small molecules - fatty acids, cholesterol, and glycerol, monosaccharides, and amino acids - within the lumen of the gastrointestinal tract and absorbed into the body principally through enterocytes in the small intestine. Some of the hydrolases that catalyze these reactions are secreted into the gastrointestinal tract; others are associated with the luminal surfaces of enterocytes. Movement of the final products of digestion out of the intestinal lumen is mediated by arrays of transporters associated with the lumenal and basolateral surfaces of enterocytes (Yamada 2015).