Secretions through the intestine

Código SN03-E0006-I

VIEW:272 DATA:2020-03-20

3.1- Structure of the mucosa

3.2- Intestinal secretions: mucus, solution of electrolytic composition similar to plasma, enteropeptidase and scaly cells.

Pancreatic secretions

4.1- Exocrine and endocrine pancreas.

4.2 Structure of the exocrine pancreas: lobes, acini and ducts.

4.3- Water and electrolytes: the main and the relationship between concentration and rhythm of secretion. Secretion in the acini and in the ducts and, as far as these, differences between the several segments. Cellular mechanisms of secretion and modulation of secretin and cholecystokinin (CCK).

4.4- Enzymes. The enzymes are secreted by the acini of the pancreatic glands. Intestinal cholecystokinin is the important hormonal stimulus, which is potentiated by secretin. Gastrin occupies the CCK receptor, because the molecules are similar, but the stimulatory effect is little. Cholinergic parasympathetic innervation stimulates the secretion of proteins.

4.4.1- Proteases. Proteases, for obvious reasons, are secreted in the form of inactive proenzymes. Enterynuclein secreted by the small intestine hydrolyzes trypsinogen to trypsin which, once produced, cleaves more trypsinogen and the precursors of chymotrypsin, carboxypeptidase A and B and elastase. Under the catalysis by these enzymes the proteins are converted to amino acids and small peptides. Amino acids and peptides with up to four amino acids are carried by apical membrane carriers. Peptides are hydrolyzed by proteases into intracellular organelles. Small protease inhibitory peptides are also produced by acinar cells. These bind with high affinity to the respective proteases and keep them inactive. Prevent proteolytic action by early activation of proteases still in the ducts.

4.4.2- to -1.4-amylase. In everything similar to salivating.

4.4.3- Lipases. The triacylglycerol hydrolase hydrolyzes ester bonds 1 and 1 'triglycerides, producing monoglycerides. They are lipases that act at the lipid-water interface and must be protected from bile acids by colipase, also pancreatic secretion. Emulsification of fats is essential for efficient lipase action. The hydrolase cholesterol esters  produces cholesterol and fatty acids. Finally, phospholipase A? hydrolyzes the ester bond of the phospholipids, producing fatty acid and lysophosphatidyl.

4.4.4-RNAase and DNAase

4.5- Control of secretion. Cephalic, gastric and intestinal phases.

4.5.1- Acids: Gastrin, CCK ACh and subst. P stimulate secretion via InsP and DAG as messengers. Insulin have on the acini the trophic and stimulating effect of the synthesis and secretion of the granules. Somatostine has an inhibitory effect.

4.5.2- Pipes: Secretin and VIP stimulate secretion. The stimulus is amplified by the simultaneous action of CCK. ACh has no effects while somatostatin, glucagon and pancreatic peptide have an inhibitory effect.

4.5.3- Secretin and CCK are hormones produced by the mucosa of the small intestine, in the regions of the duodenum and upper jejunum. The first is released when the pH of the chyme entering the duodenum is acid, less than 5. Cholecystokinin is released when in the lumen of the small intestine there are fats or peptides or amino acids.

Liver and biliary secretion .

Bile is a solution to be excreted which, because of the physico-chemical properties of bile salts and phospholipids, plays a role in the digestion of lipid absorption. The properties mentioned are the ability to emulsify fats and the formation of micelles which aggregate the products of digestion and facilitate their absorption.

5.2- A bile.

5.2.1 The most important organic solutes are bile salts, cholesterol, lecithin, and bile pigments. The electrolytes are Na +, K +, Cl - and bicarbonate, which makes it alkaline.

5.2.1- Secretion by hepatocytes and ducts. The hepatocytes stimulate them to CCK and the ducts are stimulated by secretin. The bile salts reabsorbed into the ileum are secreted again. About 10% are excreted in the faeces and replaced with hepatic synthesis. Choleretic.

5.2.2- Concentration in the gallbladder. Gallstones. Bladder emptying: parasympathetic and cholecystokinin.

Guiding questions of the study.

Discuss pancreatic, organic and inorganic secretion:

The. Components and action in the digestion process.

B. Cellular mechanisms of secretion.

W. Neural and endocrine control of secretion processes.




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