Pancreatic juice generally refers to the human bodypancreasColorless and odorlessAlkaline solution。The inorganic substances in pancreatic juice are mainly water and bicarbonate.The organic matter in pancreatic juice is a variety of digestive enzymes, which can act on the three food components of sugar, fat and proteinDigestive juiceThe most important one of.Pancreatic amylaseIt can decompose starch intomalt dust, pancreatic maltase can decompose maltose into glucose.Pancreatic lipase can decompose neutral fats into glycerol and fatty acids.
Chinese name
Pancreatic juice
Foreign name
Pancreatic juice
Substantive
Colorless and odorless alkaline solution
Features
1~2 liters of secretion
Generation
The exocrine secretion of the pancreas is pancreatic juice
The pancreas has both endocrine and exocrine functions.Endocrine function is mainly related to glucose metabolism.The exocrine secretion of the pancreas is pancreatic juice. Among all digestive juices, its digestive power is the strongest. It has digestive enzymes that can decompose three major nutrients[1]。
Nature action
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Pancreatic juice is a colorless and tasteless alkaline liquid, with a pH of 7.8~8.4. Its osmotic pressure is equal to that of plasma. The daily secretion of adults is 1~2L.In addition to water, pancreatic juice also contains inorganic substances, such as sodium ions, hydrogen ions, bicarbonate ions, etc;Organic matters are mainly various digestive enzymes[1]。
1. Bicarbonate from pancreatic ductepithelial cellsSecretion.There are abundantcarbonic anhydrase, can catalyze COtwoAnd HtwoO combines to form carbonic acid, which is then dissociatedBicarbonateIon, its concentration can reach 140mmo/L, which is 5 times higher than the plasma concentration.The main physiological functions of bicarbonate are: ① neutralize the gastric acid entering the duodenum, and protect the intestinal mucosa from strong acids. ②It provides a suitable pH environment for the activities of various digestive enzymes in the small intestine.
2．Pancreatic amylaseFrom pancreatic aciniCell secretionIt is a kind of a-amylase and has activity without activation. The optimal pH is 6.7~7.0.Its physiological function is to hydrolyze starch, glycogen and other carbohydrates into dextrin, maltose and maltooligosaccharide, but cannot hydrolyze cellulose.Pancreatic amylase hydrolysis is fast and efficient. In the small intestine, starch can be completely hydrolyzed after contacting pancreatic juice for about 10 minutes.
3. Pancreatic lipase is secreted by pancreatic acinar cells and has activity without activation. The optimal pH is 7.5~8.5.Its physiological function is to decompose fat into fatty acidsMonoglycerideAnd glycerin.However, pancreatic lipase needs the presence of coesterase secreted by the pancreas to decompose fat. The latter has a high affinity for bile salt, which makes pancreatic lipase, coesterase and bile salt form a complex, which helps pancreatic lipase anchor on the surface of fat drops to play its role and prevent bile salt from removing pancreatic lipase from the fat surface.In addition, pancreatic juice also contains cholesterol esterase, which hydrolyzes cholesterol esters into cholesterol and fatty acids;Phospholipase A2 hydrolyzes lecithin toLysolecithin。Lysophosphatidylcholine can destroy the cell membrane structure,acute pancreatitisIn patient's serumPhospholipase A2The level increases.
4．Proteolytic enzymeSecreted by pancreatic acinar cells in the form of zymogen, mainlyTrypsin、Chymotrypsin、elastaseCarboxypeptidase.TrypsinogenIt can be activated to trypsin by intestinal activating enzyme (intestinal kinase), and the trypsin produced can also activate trypsinogen (self activation);Trypsin can also activateChymotrypsinogen, elastase and carboxypeptidase, so that they can be converted into corresponding enzymes with activity.Physiological function: Trypsin and chymotrypsin can decompose protein into urea and peptone, and their synergistic effect can further decompose protein into small molecular polypeptides and amino acids.Peptides can be decomposed into amino acids by elastase or carboxypeptidase.There are also RNA enzyme and DNA enzyme in pancreatic juice, which can hydrolyze nucleic acid intoMononucleotide。In addition, chymotrypsin has strong milk clotting effect.
Regulation of secretion
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In the non digestive period, pancreatic juice is almost not secreted or secreted very little. After eating, pancreatic juice secretion increases. Food is a natural stimulus for pancreatic juice secretion.Pancreatic fluid secretion is regulated by nerve and humoral factors, but mainly by humoral regulation.
1. Nerve can regulate the shape and smell of food and the stimulation of food on the mouth, pharynx, esophagus, gastrointestinal and other receptors through conditioned reflex andUnconditioned reflexIt causes pancreatic juice secretion.The reflex efferent nerve is mainly the vagus nerve, and its terminals are releasedacetylcholine, mainly acting on pancreatic acinar cellsDuctal cellWeak effect.Therefore, when the vagus nerve is excited, the secretion of water and bicarbonate is less, and the content of trypsin is higher.
2. Body fluid regulation
(1) Secretin is a polypeptide hormone secreted by S cells of upper intestinal mucosa.The strongest stimulator of its secretion is hydrochloric acid, followed byProteolysisThe products, fatty acids and sugars have no stimulating effect.Pancreatin acts on pancreatic duct epithelial cells through blood circulation, causing a large amount of pancreatic juice secretion, which contains more water and bicarbonate, but less trypsin.
(2) Cholecystokinin (CCK), also known as trypsin, is a polypeptide hormone secreted by I cells of small intestinal mucosa.Protein decomposition products, fatty acids, hydrochloric acid and fat can stimulate its secretion, and sugars have no stimulation.Physiological function of CCK: ① It acts on pancreatic acinar cells and promotes the secretion of pancreatic enzymes in pancreatic juice (hence called trypsin). ②Stimulate gallbladder contraction and discharge bile. ③Promote pancreatic tissue protein andRibonucleic acidIt has nutritional effect on pancreatic tissue.
Pancreatin and CCK have synergistic effect on promoting pancreatic secretion.In addition, secretin can also promote the secretion of pancreatic enzymes.vasoactive intestinal peptideIt can promote the secretion of water and bicarbonate in pancreatic juice, andGlucagon, somatostatin, pancreatic polypeptideCalcitonin gene-related peptideIt can inhibit the secretion of pancreas.
3. Feedback regulation of pancreatic juice secretion
Recent studies have shown that protein decomposition products and fatty acids can stimulate the secretion of CCK releasing peptide (CCK-RP) from small intestinal mucosa. CCK-RP mediates the secretion of CCK from I cells, thus promoting the secretion of pancreatin, which in turn causes the inactivation of CCK-RP, thus feedback inhibiting the secretion of CCK and pancreatin.Its meaning is throughnegative feedback regulationPrevent excessive secretion of trypsin[1]。
