Chemical digestion is the chemical breakdown of food into simpler compounds. The food is broken down so that the body can absorb the nutrients from the food, and the blood can absorb those nutrients. Proteins are broken down to amino acids, carbohydrates are broken down to sugars, and fats are broken down to fatty acids and glycerol.
Chemical digestion does begin in the mouth. The first phase begins in the mouth with salivary amylase starting to hydrolyze starch the second you put food in into your mouth. After the food has been sufficiently broken down, it is swallowed and travels to the stomach through the esophagus.
When the food reaches the stomach (during the second stage), hormones trigger the body to release enzymes which digest and break down the food. Pepsin is the enzyme that breaks down many proteins in food. The chemical digestion of carbohydrates continues here. In humans, this stage takes about one - two hours. Next, the food is moved into the small intestine.
After leaving the stomach (but still in the second stage), the food is now a thick liquid called chyme. The chyme moves through the small intestines. It is exposed to an important liquid called bile. Bile changes fats in the chyme into a form that allows chemical digestion. During this stage of the digestive process, the small intestine absorbs more nutrients from the chyme and introduces them into the bloodstream.
The third stage of chemical digestion occurs in the final area of the small intestine, called the ileum. In this area, two enzymes (called protease and carbohydrase) are released, and they complete the digestion of proteins and carbohydrates. As what is left of the originally swallowed food leaves the small intestine, it enters into the large intestine, where the chemical digestion process ends.