Digestive enzyme

Digestive enzymes take part in the chemical process of digestion, which follows the mechanical process of digestion. Food consists of macromolecules of proteins, carbohydrates, and fats that need to be broken down chemically by digestive enzymes in the mouth, stomach, pancreas, and duodenum, before being able to be absorbed into the bloodstream. Initial breakdown is achieved by chewing (mastication) and the use of digestive enzymes of saliva. Once in the stomach further mechanical churning takes place mixing the food with secreted gastric juice. Digestive gastric enzymes take part in some of the chemical process needed for absorption. Most of the enzymatic activity, and hence absorption takes place in the duodenum.

Digestive enzymes are found in the digestive tracts of animals (including humans) and in the tracts of carnivorous plants, where they aid in the digestion of food, as well as inside cells, especially in their lysosomes, where they function to maintain cellular survival.

Digestive enzymes are classified based on their target substrates: lipases split fatty acids into fats and oils; proteases and peptidases split proteins into small peptides and amino acids; amylases split carbohydrates such as starch and sugars into simple sugars such as glucose, and nucleases split nucleic acids into nucleotides.

Digestive enzymes are found throughout much of the gastrointestinal tract. In the human digestive system, the main sites of digestion are the mouth, stomach, and small intestine. Digestive enzymes are secreted by different exocrine glands including salivary glands, gastric glands, secretory cells in the pancreas, and secretory glands in the small intestine. In some carnivorous plants plant-specific digestive enzymes are used to break down their captured organisms.

Complex food substances that are eaten must be broken down into simple, soluble, and diffusible substances before they can be absorbed. In the oral cavity, salivary glands secrete an array of enzymes and substances that aid in digestion and also disinfection. They include the following:

There are two types of salivary glands:

The enzymes that are secreted in the stomach are gastric enzymes. The stomach plays a major role in digestion, both in a mechanical sense by mixing and crushing the food, and also in an enzymatic sense, by digesting it. The following are enzymes produced by the stomach and their respective function:

The pancreas is both an endocrine, and an exocrine gland, in that it functions to produce endocrinic hormones released into the circulatory system (such as insulin, and glucagon), to control glucose metabolism, and also to secrete digestive / exocrinic pancreatic juice, which is secreted eventually via the pancreatic duct into the duodenum. Digestive or exocrine function of pancreas is as significant to the maintenance of health as its endocrine function.