Digestive hormones secretin

The return of the bile salts to the liver from the small intestine is the most potent stimulus of bile secretion. In fact, these bile salts may cycle two to five times during each meal. The intestinal hormone secretin, which is released in response to acid in the duodenum, enhances aqueous alkaline secretion by the liver. Secretin has no effect on the secretion of bile salts. During the cephalic phase of digestion, before food even reaches the stomach or intestine, parasympathetic stimulation, by way of the vagus nerve, promotes bile secretion from the liver. 

Most pancreatic secretion takes place during the intestinal phase. The intestinal hormone secretin stimulates release of a large volume of pancreatic juice with a high concentration of bicarbonate ion. Secretin is released in response to acidic chyme in the duodenum (maximal release at pH < 3.0). The intestinal hormone cholecystokinin is released in response to the presence of the products of protein and lipid digestion. Cholecystokinin then stimulates the release of digestive enzymes from the pancreas. 

As the acidic stomach contents pass into the small intestine, the low pH triggers secretion of the hormone secretin into the blood. Secretin stimulates the pancreas to secrete bicarbonate into the small intestine to neutralize the gastric HC1, abruptly increasing the pH to about 7. (All pancreatic secretions pass into the small intestine through the pancreatic duct.) The digestion of proteins now continues in the small intestine. Arrival of amino acids in the upper part of the intestine (duodenum) causes release into the blood of the hormone... 

The major enzyme that digests dietary triacylglycerols is a lipase produced in the pancreas. Pancreatic lipase is secreted along with another protein, colipase, along with bicarbonate, which neutralizes the acid that enters the intestine with partially digested food from the stomach. Bicarbonate raises the pH of the contents of the intestinal lumen into a range (pH 6) that is optimal for the action of all of the digestive enzymes of the intestine. Bicarbonate secretion from the pancreas is stimulated by the hormone secretin, which is released from the intestine when acid enters the duodenum. 

Pancreas a vertebrate organ producing a digestive secretion which enters the adjacent duodenum in response to the hormones Secretin (see) and Cholecys-tokinin (see). It also contains about 1 million islets of Langerhans, each with a diameter of ISO un these have a rich blood supply and are innervated with unmyelinated nerve fibers. The islets contain various types of hormone-producing cells, the A cells which produce Glucagon (see), the B cells which make Insulin (see) and the D cells which manufacture Gastrin (see). 

The pancreas is the most important site of production of digestive enzymes proteinases, peptidases, lipases, nucleases, etc. (cf. Chapt. VII-9, VIII-1, and XII-2). The amount of enzymes produced has been estimated to be 15-30 gm per day, which is considerable. The pancreatic juice, itself alkaline, enters the intestine and first neutralizes the acidity coming from the stomach. When acidic food pulp passes the pylorus, the latter stimulates the pancreas to elaborate more of its digestive enzymes. The secretion of pancreatic juice is regulated by tissue hormones ( secretin, Chapt. XX-12). 

Figure 6.1 Acids and bases exist in the human body and are necessary for its proper function, including the function of the digestion process. When food is swallowed, it is attacked by stomach acids. The stomach acids need to be neutralized before food can continue down the digestive tract. A hormone called secretin monitors the pH balance in the small intestine and sends chemical signals to other parts of the body, thereby regulating pH balance.

Release of zymogens The release and activation of the pancreatic zymogens is mediated by the secretion of cholecystokinin and secretin, two polypeptide hormones of the digestive tract (see p. 174). 

Know the action of hormones involved in the digestion and metabolism of food substances insulin, glucagon, secretin, gastrin, and cholecystokinin. Know their chemical and physiologic properties and what controls their blood levels. 

Both the stomach and the small intestine elaborate peptide hormones into the bloodstream, which is crucial in initiating food digestion. The most important hormones of this class are gastrin, secretin, and cholecystokinin. Their structures are displayed in Figure 16.13. 

The flow of bile is lowest during fasting, mostly being diverted to the gall bladder for concentrating. When chyme from an ingested meal enters the small intestine, acid and partially digested fats and proteins stimulate secretion of the enteric hormones cholecystokinin and secretin. 

The duodenum is the shortest part of the small intestine, where most chemical digestion occurs. The duodenum releases secretin, a hormone, which suppresses gastric acid. Cholecystokinin, a hormone, is released by the duodenum that simulates flow of bile from the gallbladder into the duodenum. Bile (produced by the liver), trypsin, chymotrypsin, lipase, and amylase (all produced by the pancreas) digest carbohydrates, protein, and fat in preparation for absorption in the small intestine. The duodenum connects the stomach to the jejunum. The jejunum is the second division of the small intestine and connects the duodenum to the ileum. The ileum is the end of the small intestine. 

We have previously demonstrated stimulation of increments in blood insulin concentration with crude and purified preparations of porcine secretin (ll, 12). We report here further investigation of the effects of hormones known to regulate digestive secretions, on the endocrine response of the pancreas to the intravenous administration of glucose or arginine in man. These studies have been carried out with preparations of porcine secretin and pancreozymin of high specific activity, supplied by... 

Secretin Gastrointestinal hormone produced in the duodenum that stimulates the secretion of pancreatic juices rich in digestive enzymes and buffer salts. 

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