Class of enzymes
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 acid. 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.
Types.
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.
Mouth.
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:
Of note is the diversity of the salivary glands. There are two types of salivary glands:
Stomach.
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: 
Pancreas.
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.
Two of the population of cells in the pancreatic parenchyma make up its digestive enzymes:
Pancreatic juice, composed of the secretions of both ductal and acinar cells, contains the following digestive enzymes:
Some of the preceding endogenous enzymes have pharmaceutical counterparts (pancreatic enzymes) that are administered to people with exocrine pancreatic insufficiency.
The pancreas's exocrine function owes part of its notable reliability to biofeedback mechanisms controlling secretion of the juice. The following significant pancreatic biofeedback mechanisms are essential to the maintenance of pancreatic juice balance/production:
Duodenum.
The following enzymes/hormones are produced in the duodenum:
Throughout the lining of the small intestine there are numerous brush border enzymes whose function is to further break down the chyme released from the stomach into absorbable particles. These enzymes are absorbed whilst peristalsis occurs. Some of these enzymes include:
Plants.
In carnivorous plants, digestive enzymes and acids break down insects and in some plants small animals. In some plants, the leaf collapses on the prey to increase contact, others have a small vessel of digestive liquid. Then digestion fluids are used to digest the prey to get at the needed nitrates and phosphorus. The absorption of the needed nutrients are usually more efficient than in other plants. Digestive enzymes independently came about in carnivorous plants and animals.
Some carnivorous plants like the "Heliamphora" do not use digestive enzymes, but use bacteria to break down the food. These plants do not have digestive juices, but use the rot of the prey.
Some carnivorous plants digestive enzymes:
Clinical significance.
Alpha-glucosidase inhibitors and alpha amylase inhibitors are found in several raw plants such as cinnamon. They are used as anti-diabetic drugs. Studies have shown that the use of raw cinnamon offers potential anti-diabetic therapeutic use.
References.
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