Digestive enzyme

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Digestive enzymes are enzymes that break down polymeric macromolecules into their smaller building blocks, in order to facilitate their absorption by the body. Digestive enzymes are found in the digestive tracts of animals (including humans) and in the traps 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 diverse and are found in the saliva secreted by the salivary glands, in the stomach secreted by cells lining the stomach, in the pancreatic juice secreted by pancreatic exocrine cells, and in the intestinal (small and large) secretions, or as part of the lining of the gastrointestinal tract.

Digestive enzymes are classified based on their target substrates:

In the human digestive system, the main sites of digestion are the oral cavity, the stomach, and the small intestine. Digestive enzymes are secreted by different exocrine glands including:


Complex food substances that are taken by animals and humans 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:[1]

Of note is the diversity of the salivary glands. There are two types of salivary glands:


The enzymes that are secreted in the stomach are called 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, hormones or compounds produced by the stomach and their respective function:

Of note is the division of function between the cells covering the stomach. There are four types of cells in the stomach:

Secretion by the previous cells is controlled by the enteric nervous system. Distention in the stomach or innervation by the vagus nerve (via the parasympathetic division of the autonomic nervous system) activates the ENS, in turn leading to the release of acetylcholine. Once present, acetylcholine activates G cells and parietal cells.


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 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, is made up of the following digestive enzymes:[2]

Pancreas's exocrine function owes part of its immaculate function to bio-feedback mechanisms controlling secretion of its juice. The following significant pancreatic bio-feedback mechanisms are essential to the maintenance of pancreatic juice balance/production:[3]

Small intestine[edit]

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. Some of these enzymes include:


  1. ^ Brown, Thomas A. "Rapid Review Physiology." Mosby Elsevier, 1st Ed. p. 235
  2. ^ Bowen, R. [1] "Exocrine Secretion of the Pancreas"
  3. ^ Brown, Thomas A. "Rapid Review Physiology." Mosby Elsevier, 1st Ed. p. 244
  4. ^ Morino, P; Mascagni, F; McDonald, A; Hökfelt, T (1994). "Cholecystokinin corticostriatal pathway in the rat: Evidence for bilateral origin from medial prefrontal cortical areas". Neuroscience 59 (4): 939–52. doi:10.1016/0306-4522(94)90297-6. PMID 7520138.