Digestion is accomplished by both mechanical and chemical means. While the two methods of digestion are different, they share a common goal. Mechanical digestion, which occurs by the physical action of the body on food, and chemical digestion, which occurs through the use of enzymes and acid, both work to break down food to facilitate the absorption of nutrients. Each of these processes begins in the mouth and continues to act in concert throughout the digestive process.
Both mechanical and chemical digestion begin to break down food when it enters the mouth. The grinding and cutting action of the teeth on the food breaks it into small pieces. The tongue also contributes to the mechanical digestion that takes place within the mouth by mashing the food around, ensuring that it is evenly chewed. The tongue also facilitates the beginning of the chemical digestion by working to mix the chewed food with the saliva in the mouth. Saliva contains a digestive enzyme called amylase, which is also present in the pancreas. This enzyme begins the process of chemically breaking down the food even before it is swallowed.
After the food is swallowed, mechanical and chemical digestion continue to work together to process the food consumed, extracting nutrients for use in the body. Within the stomach, enzymes such as pepsin, lipase and gelatinase break down the proteins in food for easier absorption. The churning of the stomach walls continuously mixes the food with the enzymes and stomach acid, using mechanical means to improve the efficiency of chemical digestion. As food moves from the stomach into the intestines, it is subject to a process called peristalsis, which refers to the movement of food through the intestines by muscle movement. As the food moves, it continues to be mashed by this process, ensuring that all of the remaining nutrients can be broken down by enzymes such as maltase, lactase and chymotrypsin.