Which Digestive Enzymes Digest Food?
Digestion is actually the breakdown of food into smaller molecules that can be readily absorbed and utilized by the body. The process of digestion includes many enzymes that are necessary for the digestion of food.
Oral Cavity (Mouth)
The process of digestion begins in the mouth. The mouth is responsible for both mechanical digestion, the actual mastication (chewing) for the breakdown of food, and chemical digestion. Foods are chemically digested in the mouth by saliva, which contains the digestive enzyme amylase. Amylase is an enzyme that is responsible for the breakdown of starches into smaller molecules that will be more readily digested within the stomach.
From the mouth, food is swallowed and delivered to the stomach, where further digestion occurs. The stomach is responsible for the chemical digestion of food by hydrochloric acid (stomach acid) and the presence of several digestive enzymes, known as gastric enzymes. The main gastric enzyme of the stomach is known as pepsin. Pepsin is a peptidase, meaning it breaks down proteins into smaller units, peptide fragments. The stomach also contains gelatinase, gastric amylase, and gastric lipase. Each of these enzymes is specific as to the type of protein it is responsible for degrading.
Digestive Accessory Organs: The Pancreas and Liver
While the pancreas is not a location within the digestive system where digestion actually occurs, it is an important accessory organ to the digestive system. The main digestive gland is the pancreas, responsible for the production and secretion of many digestive enzymes. The pancreas is responsible for the production of trypsin, chymotrypsin, pancreatic amylase, elastases, nucleases, steapsin, and carboxypeptidase. Once produced, these enzymes are secreted to the small intestine for use. Additionally, the liver is also involved in this digestive process. The liver produces and secretes a substance known as bile, which is stored by the gall bladder. Bile is mainly responsible for the emulsification (breakdown) of fats within the digestive system.
In addition to receiving many enzymes from the pancreas and bile from the liver, the small intestine also makes several additional enzymes necessary for the proper digestion of food. The small intestine produces maltase, isomaltase, sucrase, lactase, and intestinal lipase. These enzymes together are known as succus entericus and digest disaccharides into monosaccharides. The small intestine is the location of the digestive system where the majority of both digestion and absorption occurs.
Digestion: How is it Controlled?
The process of digestion is mainly controlled by hormones. There are three hormones that are mainly associated with digestion control, including secretin, gastrin, and CCK. The hormone CCK signals the gall bladder to empty and stimulates the pancreas to produce enzymes. Gastrin signals the stomach to produce hydrochloric acid. Secretein is the hormone that stimulates the stomach to produce enzymes and the liver to produce bile. Additionally, there are also hormones that regulate appetite. These two hormones are known as ghrelin and peptide YY. Peptide YY is produced within the alimentary tract and inhibits appetite after the consumption of a meal. Ghrelin accomplishes the exact opposite and signals hunger when there is an absence of food within the digestive system.