Editing Digestive enzyme

{{Short description|Class of enzymes}}
{{About|the naturally produced enzymes|the medication|Pancreatic enzymes (medication)}}
{{more citations needed|date=December 2016}}
[[File:Digestive Enzymes.svg|thumb|Diagram of the digestive enzymes in the small intestine and pancreas]]
'''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.<ref name="Patricia">{{cite journal |last1=Patricia |first1=Justin J. |last2=Dhamoon |first2=Amit S. |title=Physiology, Digestion |url=https://www.ncbi.nlm.nih.gov/books/NBK544242/ |website=StatPearls |publisher=StatPearls Publishing |date=2024|pmid=31334962 }}</ref> Initial breakdown is achieved by [[chewing]] (mastication) and the use of digestive [[enzyme]]s 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 (chemistry)|absorption]]. Most of the enzymatic activity, and hence absorption takes place in the duodenum.<ref>{{Cite web |date=2018-07-22 |title=22.10C: Digestive Processes of the Small Intestine |url=https://med.libretexts.org/Bookshelves/Anatomy_and_Physiology/Anatomy_and_Physiology_(Boundless)/22%3A_Digestive_System/22.10%3A_The_Small_Intestine/22.10C%3A_Digestive_Processes_of_the_Small_Intestine |access-date=2023-08-14 |website=Medicine LibreTexts |language=en}}</ref><ref name="Heda">{{cite journal |last1=Heda |first1=Rajiv |last2=Toro |first2=Fadi |last3=Tombazzi |first3=Claudio R. |title=Physiology, Pepsin |url=https://pubmed.ncbi.nlm.nih.gov/30725690/ |website=StatPearls |publisher=StatPearls Publishing |date=2024|pmid=30725690 }}</ref>
 
Digestive enzymes are found in the digestive tracts of animals (including humans) and in the tracts of [[carnivorous plant]]s, where they aid in the digestion of food, as well as inside [[cell (biology)|cells]], especially in their [[lysosome]]s, where they function to maintain cellular survival.<ref>{{Cite journal |last1=Freund |first1=Matthias |last2=Graus |first2=Dorothea |last3=Fleischmann |first3=Andreas |last4=Gilbert |first4=Kadeem J |last5=Lin |first5=Qianshi |last6=Renner |first6=Tanya |last7=Stigloher |first7=Christian |last8=Albert |first8=Victor A |last9=Hedrich |first9=Rainer |last10=Fukushima |first10=Kenji |date=2022-05-23 |title=The digestive systems of carnivorous plants |url=http://dx.doi.org/10.1093/plphys/kiac232 |journal=Plant Physiology |volume=190 |issue=1 |pages=44–59 |doi=10.1093/plphys/kiac232 |pmid=35604105 |issn=0032-0889|pmc=9434158 }}</ref><ref>{{Cite web |title=Enzymes: What Are Enzymes, Pancreas, Digestion & Liver Function |url=https://my.clevelandclinic.org/health/articles/21532-enzymes |access-date=2023-08-14 |website=Cleveland Clinic |language=en}}</ref>

Digestive enzymes are classified based on their target [[enzyme substrate|substrate]]s: [[lipase]]s split [[fatty acid]]s into [[fat]]s and [[oil]]s;<ref>{{Cite web |title=Lipase {{!}} Fat-digesting, Pancreatic, Lipolytic {{!}} Britannica |url=https://www.britannica.com/science/lipase |access-date=2023-08-14 |website=www.britannica.com |language=en}}</ref>
[[protease]]s and [[peptidase]]s split [[protein]]s into small [[peptides]] and [[amino acid]]s;<ref>{{Cite web |title=Proteolytic enzyme {{!}} Description, Types, & Functions {{!}} Britannica |url=https://www.britannica.com/science/proteolytic-enzyme |access-date=2023-08-14 |website=www.britannica.com |language=en}}</ref>
[[amylase]]s split [[carbohydrate]]s such as [[starch]] and [[sugar]]s into [[Monosaccharide|simple sugars]] such as [[glucose]],<ref>{{Cite web |date=2017-06-14 |title=3.3: Digestion and Absorption of Carbohydrates |url=https://med.libretexts.org/Courses/American_Public_University/APUS%3A_An_Introduction_to_Nutrition_(Byerley)/APUS%3A_An_Introduction_to_Nutrition_1st_Edition/03%3A_Carbohydrates/3.03%3A_Digestion_and_Absorption_of_Carbohydrates |access-date=2023-08-14 |website=Medicine LibreTexts |language=en}}</ref>
and [[nuclease]]s split [[nucleic acid]]s into [[nucleotides]].<ref>{{Cite web |title=Pancreatic nucleases - Big Chemical Encyclopedia |url=https://chempedia.info/info/pancreatic_nucleases/ |access-date=2023-08-14 |website=chempedia.info}}</ref>

==Types==
[[File:Major digestive enzymes.png|thumb|Table of the different major digestive enzymes]]
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 gland]]s, [[gastric gland]]s, secretory cells in the [[pancreas]], and secretory glands in the [[small intestine]]. In some [[carnivorous plant]]s 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:<ref>Brown, Thomas A. "Rapid Review Physiology." Mosby Elsevier, 1st Ed. p. 235</ref>
* [[Lingual lipase]]: [[Lipid]] digestion initiates in the mouth. Lingual lipase starts the digestion of the lipids/fats.
* [[alpha-amylase|Salivary amylase]]: Carbohydrate digestion also initiates in the mouth. Amylase, produced by the salivary glands, breaks complex carbohydrates, mainly cooked starch, to smaller chains, or even simple sugars. It is sometimes referred to as [[ptyalin]].
* [[Lysozyme]]: Considering that food contains more than just essential nutrients, e.g. bacteria or viruses, the lysozyme offers a limited and non-specific, yet beneficial antiseptic function in digestion.

Of note is the diversity of the salivary glands. There are two types of salivary glands:
* [[Serous gland]]s: These glands produce a secretion rich in water, electrolytes, and enzymes. A great example of a serous oral gland is the [[parotid]] gland.
* Mixed glands: These glands have both [[serous cell]]s and [[mucous cell]]s, and include sublingual and submandibular glands. Their secretion is mucinous and high in [[viscosity]].

===Stomach===
{{unreferenced section|date=December 2016}}
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: 
* [[Pepsin]] is the main gastric enzyme. It is produced in the stomach by [[gastric chief cell]]s in its inactive form [[pepsinogen]], which is a [[zymogen]]. Pepsinogen is then activated by the stomach acid into its active form, pepsin. Pepsin breaks down the protein in the food into smaller particles, such as [[peptide]] fragments and [[amino acids]]. Protein digestion, therefore, primarily starts in the stomach, unlike carbohydrate and lipids, which start their digestion in the mouth (however, trace amounts of the enzyme [[kallikrein]], which catabolises certain protein, is found in saliva in the mouth).
* [[Gastric lipase]]: Gastric lipase is an acidic [[lipase]] secreted by the [[gastric chief cell]]s in the [[fundic glands|fundic]] mucosa of the stomach.  It has a pH level of 3–6. Gastric lipase, together with lingual lipase, comprise the two acidic lipases. These lipases, unlike alkaline lipases (such as [[pancreatic lipase]]), do not require [[bile acid]] or [[colipase]] for optimal enzymatic activity. Acidic lipases make up 30% of lipid [[hydrolysis]] occurring during digestion in the human adult, with gastric lipase contributing the most of the two acidic lipases. In neonates, acidic lipases are much more important, providing up to 50% of total lipolytic activity.
* [[Cathepsin F]]: is a [[cysteine protease]].

===Pancreas===
{{Hatnote|"Pancreatic enzyme" and "pancrease" redirect to this discussion of endogenous forms. For exogenous forms, see [[Pancreatic enzymes (medication)]].}}
The pancreas is both an [[Endocrine gland|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|tissue]] make up its digestive enzymes:
* [[Ductal cells]]: Mainly responsible for production of [[bicarbonate]] (HCO<sub>3</sub>), which acts to neutralize the acidity of the stomach chyme entering duodenum through the pylorus. Ductal cells of the pancreas are stimulated by the hormone [[secretin]] to produce their bicarbonate-rich secretions, in what is in essence a bio-feedback mechanism; highly acidic stomach chyme entering the duodenum stimulates duodenal cells called "S cells" to produce the hormone secretin and release  to the bloodstream. Secretin having entered the blood eventually comes into contact with the pancreatic ductal cells, stimulating them to produce their bicarbonate-rich juice. Secretin also inhibits production of [[gastrin]] by "G cells", and also stimulates acinar cells of the pancreas to produce their pancreatic enzyme.
* [[Centroacinar cells|Acinar cells]]: Mainly responsible for production of the inactive pancreatic enzymes ([[zymogens]]) that, once present in the small bowel, become activated and perform their major digestive functions by breaking down proteins, fat, and DNA/RNA. Acinar cells are stimulated by [[cholecystokinin]] (CCK), which is a hormone/neurotransmitter produced by the intestinal cells (I cells) in the duodenum. CCK stimulates production of the pancreatic zymogens.

[[Pancreatic juice]], composed of the secretions of both ductal and acinar cells, contains the following digestive enzymes:<ref>Bowen, R. [http://www.vivo.colostate.edu/hbooks/pathphys/digestion/pancreas/exocrine.html] "Exocrine Secretion of the Pancreas"</ref>
* [[Trypsinogen]], which is an inactive (zymogenic) protease that, once activated in the duodenum into [[trypsin]], breaks down proteins at the basic amino acids. Trypsinogen is activated via the duodenal enzyme [[enterokinase]] into its active form trypsin.
* [[Chymotrypsinogen]], which is an inactive (zymogenic) protease that, once activated by duodenal enterokinase, turns into [[chymotrypsin]] and breaks down proteins at their [[aromatic amino acids]]. Chymotrypsinogen can also be activated by trypsin.
* [[Carboxypeptidase]], which is a protease that takes off the terminal amino acid group from a protein
* Several [[elastase]]s that degrade the protein [[elastin]] and some other proteins
* [[Pancreatic lipase]] that degrades triglycerides into two fatty acids and a [[monoglyceride]]<ref>Pandol SJ. [https://www.ncbi.nlm.nih.gov/books/NBK54127/ The Exocrine Pancreas]. San Rafael (CA): Morgan & Claypool Life Sciences; 2010</ref>
* [[Sterol esterase]]
* [[Phospholipase]]
* Several [[nuclease]]s that degrade nucleic acids, like [[DNAase]] and [[RNAase]]
* [[Pancreatic amylase]] that breaks down starch and [[glycogen]] which are alpha-linked glucose polymers. Humans lack the cellulases to digest the carbohydrate [[cellulose]] which is a beta-linked glucose polymer.

Some of the preceding endogenous enzymes have pharmaceutical counterparts ([[pancreatic enzymes (medication)|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:<ref>Brown, Thomas A. "Rapid Review Physiology." Mosby Elsevier, 1st Ed. p. 244</ref>
* [[Secretin]], a hormone produced by the duodenal "S cells" in response to the stomach chyme containing high hydrogen atom concentration (high acidity), is released into the blood stream; upon return to the digestive tract, secretion decreases gastric emptying, increases secretion of the pancreatic ductal cells, as well as stimulating pancreatic acinar cells to release their zymogenic juice.
* [[Cholecystokinin]] (CCK) is a unique peptide released by the duodenal "I cells" in response to chyme containing high fat or protein content. Unlike secretin, which is an endocrine hormone, CCK actually works via stimulation of a neuronal circuit, the end-result of which is stimulation of the acinar cells to release their content. CCK also increases gallbladder contraction, resulting in [[bile]] squeezed into the [[cystic duct]], [[common bile duct]] and eventually the duodenum. Bile of course helps absorption of the fat by emulsifying it, increasing its absorptive surface. Bile is made by the liver, but is stored in the gallbladder.
* [[Gastric inhibitory peptide]] (GIP) is produced by the mucosal duodenal cells in response to chyme containing high amounts of carbohydrate, proteins, and [[fatty acids]]. Main function of GIP is to decrease gastric emptying.
* [[Somatostatin]] is a hormone produced by the mucosal cells of the duodenum and also the "delta cells" of the pancreas. Somatostatin has a major inhibitory effect, including on pancreatic  production.

===Duodenum===

The following enzymes/hormones are produced in the [[duodenum]]:
* [[secretin]]: This is an endocrine hormone produced by the duodenal "[[S cell]]s" in response to the acidity of the gastric chyme.
* Cholecystokinin (CCK) is a unique peptide released by the duodenal "I cells" in response to chyme containing high fat or protein content. Unlike secretin, which is an endocrine hormone, CCK actually works via stimulation of a neuronal circuit, the end-result of which is stimulation of the acinar cells to release their content.<ref>{{cite journal|pmid=7520138|year=1994|last1=Morino|first1=P|last2=Mascagni|first2=F|last3=McDonald|first3=A|last4=Hökfelt|first4=T|title=Cholecystokinin corticostriatal pathway in the rat: Evidence for bilateral origin from medial prefrontal cortical areas|volume=59|issue=4|pages=939–52|journal=Neuroscience|doi=10.1016/0306-4522(94)90297-6|s2cid=32097183}}</ref> CCK also increases gallbladder contraction, causing release of pre-stored bile into the cystic duct, and eventually into the common bile duct and via the [[ampulla of Vater]] into the second anatomic position of the duodenum. CCK also decreases the tone of the [[sphincter of Oddi]], which is the sphincter that regulates flow through the ampulla of Vater. CCK also decreases gastric activity and decreases gastric emptying, thereby giving more time to the pancreatic juices to neutralize the acidity of the gastric chyme.
* Gastric inhibitory peptide (GIP): This peptide decreases gastric motility and is produced by duodenal mucosal cells.
* [[motilin]]: This substance increases gastro-intestinal motility via specialized receptors called "motilin receptors".
* somatostatin: This hormone is produced by duodenal mucosa and also by the [[delta cells]] of the pancreas. Its main function is to inhibit a variety of secretory mechanisms.

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:
* Various [[exopeptidases]] and [[endopeptidases]] including [[dipeptidase]] and [[aminopeptidase]]s that convert peptones and polypeptides into amino acids.<ref>{{cite web |url=http://www.vivo.colostate.edu/hbooks/pathphys/digestion/smallgut/bbenzymes.html |title=Small Intestinal Brush Border Enzymes }}</ref>
* [[Maltase]]: converts maltose into glucose.
* [[Lactase]]: This is a significant enzyme that converts lactose into glucose and galactose.  A majority of Middle-Eastern and Asian populations lack this enzyme.  This enzyme also decreases with age.  As such [[lactose intolerance]] is often a common abdominal complaint in the Middle-Eastern, Asian, and older populations, manifesting with bloating, abdominal pain, and [[osmotic diarrhea]].
* [[Sucrase]]: converts sucrose into glucose and fructose.
* Other disaccharidases

===Plants===
In carnivorous plants, digestive enzymes and acids break down [[insect]]s and in some plants small animals. In some plants, the leaf collapses on the prey to increase contact, others have a small [[Bowl (vessel)|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.<ref>[http://carnivorousplants.org/cp/carnivory/digestion carnivorousplants.org, digestion]</ref><ref>The Uptake of Digestion Products by Drosera, by Chandler, Graeme, 1978</ref><ref>Carnivory of Byblis revisited - A simple method for enzyme testing on carnivorous plants, by Hartmeyer, Siegfried 1997</ref>

Some [[carnivorous plant]]s 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 [[Decomposition|rot]] of the prey.<ref name=McPherson2011>McPherson, S., A. Wistuba, A. Fleischmann & J. Nerz 2011. ''[[Sarraceniaceae of South America]]''. Redfern Natural History Productions, Poole.</ref>

Some carnivorous plants digestive enzymes:<ref>{{Cite journal |pmc = 5993016|year = 2018|last1 = Ravee|first1 = R.|title = Discovery of digestive enzymes in carnivorous plants with focus on proteases|journal = PeerJ|volume = 6|pages = e4914|last2 = Goh|first2 = H. H.|last3 = Goh|first3 = Hoe-Han|pmid = 29888132|doi = 10.7717/peerj.4914 | doi-access=free }}</ref>
* ''[[Hydrolytic]]  process''
* [[Esterase]] a [[hydrolase]] enzyme
* Proteases enzyme
* Nucleases enzyme
* [[Phosphatases]] enzyme
* [[Glucanases]] enzyme
* [[Peroxidases]] enzyme
* [[Ureas]] an [[organic compound]]s
* [[Chitinase]] enzyme

== Clinical significance ==

[[Alpha-glucosidase inhibitor]]s and [[alpha amylase inhibitor]]s are found in several raw plants such as [[cinnamon]].<ref name="Moreira">{{Cite journal |last1=Moreira |first1=Fernanda Duarte |last2=Reis |first2=Caio Eduardo Gonçalves |last3=Gallassi |first3=Andrea Donatti |last4=Moreira |first4=Daniel Carneiro |last5=Welker |first5=Alexis Fonseca |date=2024-10-09 |editor-last=Dardari |editor-first=Dured |title=Suppression of the postprandial hyperglycemia in patients with type 2 diabetes by a raw medicinal herb powder is weakened when consumed in ordinary hard gelatin capsules: A randomized crossover clinical trial |journal=PLOS ONE |language=en |volume=19 |issue=10 |pages=e0311501 |doi=10.1371/journal.pone.0311501 |doi-access=free |issn=1932-6203 |pmc=11463819 |pmid=39383145}}</ref><ref name="Hayward">{{Cite journal |last1=Hayward |first1=Nicholas J. |last2=McDougall |first2=Gordon J. |last3=Farag |first3=Sara |last4=Allwood |first4=J. William |last5=Austin |first5=Ceri |last6=Campbell |first6=Fiona |last7=Horgan |first7=Graham |last8=Ranawana |first8=Viren |date=2019-08-01 |title=Cinnamon Shows Antidiabetic Properties that Are Species-Specific: Effects on Enzyme Activity Inhibition and Starch Digestion |journal=Plant Foods for Human Nutrition |language=en |volume=74 |issue=4 |pages=544–552 |doi=10.1007/s11130-019-00760-8 |issn=0921-9668 |pmc=6900266 |pmid=31372918}}</ref> They are used as anti-diabetic drugs. Studies have shown that the use of raw cinnamon offers potential anti-diabetic therapeutic use.<ref name="Moreira"/><ref name="Hayward"/>

==See also==

* [[Acarbose]]
* [[Alpha-glucosidase]]
* [[Erepsin]]

==References==
{{Reflist}}

{{Digestive enzymes}}
{{Serine endopeptidases}}

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[[Category:Enzymes]]