![]() ![]() The first step in lipid digestion is emulsification, which is the transformation of large lipid droplets into much smaller droplets.Lipids include triglycerides, phospholipids, cholesterol, steroids, and fat-soluble vitamins.They do not mix with the stomach or intestinal contents. Fats not being soluble in water by their nature are both difficult to digest and absorb.Trypsin then converts chymotrypsinogen, proelastase, and procarboxypeptidase A and B to their active forms.Trypsinogen is activated to trypsin by a brush border enzyme, enterokinase.They are secreted in inactive forms that are activated in the small intestine as follows:.The proteases include trypsin, chymotrypsin, elastase, carboxypeptidase A, and carboxypeptidase B. ![]() The digestion is completed in the small intestine by the action of pancreatic and intestinal juice.Thus, in the intestine, as HCO 3 − is secreted in pancreatic fluids, duodenal pH increases, and pepsin is inactivated. When the pH is >5, pepsin is denatured.Pepsin hydrolyzes proteins into peptones and proteoses.The optimum pH for pepsin is between 1 and 3. Pepsinogen is activated to pepsin by gastric H+.Pepsin is secreted in its zymogen form as pepsinogen by the chief cells of the stomach.Digestion takes place in the stomach and the small intestine.Both endopeptidases enzymes which degrade proteins by hydrolyzing interior peptide bonds and exopeptidases enzyme that hydrolyzes one amino acid at a time from the C-terminus of proteins and peptides are involved in the digestion of proteins.Digestive products of protein can be absorbed as amino acids, dipeptides, and tripeptides Mostly, proteins must be broken down into amino acids for absorption.Dietary proteins are a source of amino acids that are utilized for the formation of various cellular substances.
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