Which of the following is true about somatostatin, insulin, and glucagon?
Correct Answer: Somatostatin blocks release of insulin and glucagon.
Description: Ans. D. Somatostatin blocks release of insulin and glucagon. (Ref. Ganong 21st fpg.427; KDT 6th/Pg. 273).Guyton physiology llth/pg. 971...........# Somatostatin inhibits Giucagon and Insulin Secretion.# Insulin, amylin, and somatostatin, elaborated by the neighbouring beta and D cells, inhibit glucagon secretion.SOMATOSTATIN:# It is GH inhibiting hormone, secreted by D-cells of pancreas and by D cells in intestinal mucosa.# It is same chemically as growth hormone inhibitory hormone.# It suppresses anterior pituitary gland function, hence suppresses TSH, ACTH and GH.6# It inhibits release of gastrin and secretin, and decreases motility of stomach, duodenum and GB.# It inhibits islets of Langerhans and reduces secretion of both, insulin and glucagon.6# It also inhibits secretion of VIP, GIP & motilin.# It does not inhibit prolactin secretion.# USES:- Beneficial in pancreatic, biliary or intestinal fistulae;- in Gastrinoma,- in management of esophageal varices (octreotide).6Glucagon and Its Functions# Glucagon, a hormone secreted by the alpha cells of the islets of Langerhans when the blood glucose concentration falls, has several functions that are diametrically opposed to those of insulin. Most important of these functions is to increase the blood glucose concentration, an effect that is exactly the opposite that of insulin.# Like insulin, glucagon is a large polypeptide. It has a molecular weight of 3485 and is composed of a chain of 29 amino acids. On injection of purified glucagon into an animal, a profound hyperglycemic effect occurs. Only 1 mg/kg of glucagon can elevate the blood glucose concentration about 20 mg/100 ml of blood (a 25 % increase) in about 20 minutes. For this reason, glucagon is also called the hyperglycemic hormone.# The major effects of glucagon on glucose metabolism are:1) Breakdown of liver glycogen (glycogenolysis) and2) Increased gluconeogenesis in the liver. Both of these effects greatly enhance the availability of glucose to the other organs of the body.3) Other Effects of Glucagon: Perhaps the most important effect is that glucagon activates adipose cell lipase, making increased quantities of fatty acids available to the energy systems of the body. Glucagon also inhibits the storage of triglycerides in the liver, which prevents the liver from removing fatty acids from the blood; this also helps make additional amounts of fatty acids available for the other tissues of the body.4) Glucagon in very high concentrations also:(a) Enhances the strength of the heart;(b) Increases blood flow in some tissues, especially the kidneys;(c) Enhances bile secretion; and(d) Inhibits gastric acid secretion. All these effects are of minimal importance in the nor function of body.# Regulation of glucagon secretion:- Increased Blood Glucose Inhibits Glucagon Secretion.- Increased Blood Amino Acids Stimulate Glucagon Secretion.- High concentrations of amino acids, as occur in the blood after a protein meal (especially the amino acids alanine and arginine), stimulate the secretion of glucagon. This is the same effect that amino acids have in stimulating insulin secretion. Thus, in this instance, the glucagon and insulin responses are not opposites.- Exercise Stimulates Glucagon Secretion.Somatostatin Inhibits Glucagon and Insulin Secretion1) increased blood glucose,2) increased amino acids,3) increased fatty acids, and4) increased cone of several of the GI hormones released from upper GI tract in response to food intake.In turn, somatostatin has multiple inhibitory effects as follows:1. Somatostatin acts locally within islets of Langerhans to depress secretion of both insulin and glucagon.2. Somatostatin decreases the motility of the stomach, duodenum, and gallbladder.3. Somatostatin decreases both secretion and absorption in the GI tract.
Category:
Biochemistry
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