PHYS 506 Anatomy and Physiology Endocrine (Pancreatic Islet Cells) MCQs Answers 2023/24

PHYS 506 Anatomy and Physiology Endocrine (Pancreatic Islet Cells) MCQs Answers 2023/24 Pancreatic Islet Cells 186. A patient presents with Whipple triad, including plasma glucose 60 mg/dL, symptomatic hypoglycemia, and improvement of symptoms with administration of glucose. CT of the abdomen is suggestive of islet cell carcinoma. Which of the following best describes the islets of Langerhans? (A) They are found primarily in the head of the pancreas. (B) They constitute approximately 30% of the pancreatic weight. (C) They contain six distinct endocrine cell types. (D) They have a meager blood supply (E) They secrete insulin and glucagon. Answer: E. The islets of Langerhans, which constitute 1% to 2% of the pancreatic weight, secrete insulin, glucagon, somatostatin, and pancreatic polypeptide. Each is secreted from a distinct cell type, A, B, D, and F, respectively. The islets are scattered throughout the pancreas, but are more plentiful in the tail than in the body or head. Insulin 187. Which of the following pancreatic secretions has a receptor with four subunits, two of which have tyrosine kinase activity? (A) Insulin (B) Glucagon (C) Somatostatin (D) Pancreatic lipase Answer: A. The insulin receptor in target tissues is a tetramer. The two β subunits have tyrosine kinase activity and autophosphorylate the receptor when stimulated by insulin. Questions 188 and 189 refer to the following figure. 188. Which one of the metabolic pathways refers to the hormone produced by the pancreatic beta cells? Answer: C. In carbohydrate metabolism, insulin is glycogenic, glycolytic, and antigluconeogenic. Thus, insulin brings about hypoglycemia by both promoting the polymerization of glucose (glycogenesis) and enhancing glucose utilization (glycolysis). In the figure, there are two glycogenic hormones: cortisol (B) and insulin (C). Cortisol, however, inhibits glucose utilization. The other hormone in this series that promotes glycolysis is epinephrine (A), which also promotes glycogenolysis. Hormone D is glucagon, a product of the pancreatic alpha cells; however, glucagon promotes glycogenolysis and inhibits glycolysis. Somatotropin (E) also causes hyperglycemia but it inhibits glycolysis without a large effect on glycogen metabolism. Epinephrine (A), cortisol (B), glucagon (D), and somatotropin (E) are all gluconeogenic hormones. These four hormones are anti-insulin hormones and are referred to as the glucose counterregulatory hormones. 189. Which one of the metabolic pathways refers to the pancreatic hormone that is elevated in type 1 diabetes mellitus? Answer: D. In type 1 diabetes, glucagon (D) is elevated because the inhibitory effect of insulin on glucagon secretion is absent. Glucagon is hyperglycemic because it is glycogenolytic, gluconeogenic, and anti-glycolytic. Also, epinephrine increases glucagon secretion in the setting of type 1 diabetes. Stimuli for Insulin Secretion 190. Which of the following is most likely to produce the greatest increase in insulin secretion? (A) Amino acids (B) Amino acids and glucose (C) Amino acids and somatostatin (D) Glucose and somatostatin Answer: B. Both amino acids and glucose stimulate insulin secretion. Further, amino acids strongly potentiate the glucose stimulus for insulin secretion. Somatostatin inhibits insulin secretion. 191. Insulin secretion is increased by: (A) Losing-weight (B) Gut hormones (C) Lowering the plasma glucose concentration (D) Somatostatin (E) Stimulation of the adrenergic nerve supply to the pancreas Answer: B. Hormones secreted by the gut, especially gastric inhibitory peptide (GIP), but also secretin and cholecystokinin, are strong promoters of insulin secretion. Regarding choice A: Generally, body weight is proportional to food intake, as is insulin secretion. High rates of insulin secretion may lead to insulin resistance, by downregulating insulin receptors in target tissues. Losing weight is accomplished by decreasing food intake, and/or increasing exercise, both of which decrease insulin secretion. Lowering insulin secretion allows the number of insulin receptors to increase, and insulin sensitivity returns to normal. Regarding choice E, β-adrenergic receptors promote, and α-adrenergic receptors inhibit, insulin secretion. Nevertheless, when the adrenergic nerve supply to the pancreas is stimulated (as during prolonged strenuous exercise), the effect of the α-receptors predominates, and insulin secretion is inhibited. Simultaneously, the secretion of glucagon is increased. 192. Which of the following hormonal responses would be expected after a meal high in protein? Insulin Glucagon Growth hormone (A) ↑ ↑ ↓ (B) ↑ ↑ ↑ (C) ↑ ↓ ↓ (D) ↓ ↓ ↑ (E) ↓ ↑ ↑ Answer: B. A protein meal stimulates all three of the hormones indicated. Metabolic Effects of Insulin 193. The effects of insulin include… (A)Depolarization of muscle cells (B) Lipolysis (C) Inhibition of glycogen synthase activity (D)Glucose transport into the pancreatic beta cell (E) Increase in secondary active transport of glucose into muscle and fat cells Answer: D. Glucose enters the beta cell by a specific glucose transporter called GLUT-2 (which also transports glucose into the hepatocyte). Glucose is phosphorylated and metabolized with the generation of adenosine 5'-triphosphate (ATP). The ATP closes the ATP-sensitive K+ channel, which leads to the depolarization of the β cell membrane and thereby activates a voltage-dependent Ca2+ channel. The resultant increase in intracellular Ca2+ stimulates insulin secretion. Insulin decreases cell membrane permeability to both Na+ and K+ , but it decreases Na+ permeability more, causing hyperpolarization of skeletal and cardiac muscle cells and adipocytes but not of liver or pancreatic cells. Insulin also promotes lipogenesis, protein anabolism, glycogenesis, and glycolysis. Insulin promotes glucose uptake by muscle and adipose tissue but not by the liver, and it promotes storage and utilization of glucose in all three tissues. Glucose storage by muscle and liver is achieved by formation of glycogen via an increase in glycogen synthase activity. Glucose transport across skeletal and cardiac muscle cells and adipocytes occurs by insulindependent facilitated diffusion via the GLUT-4 transporter. 194. Insulin exerts all of the following effects EXCEPT… (A)Hyperpolarization of skeletal muscle cells (B) Promotion of lipogenesis (C) Stimulation of glycogen synthase activity (D)Increase in secondary active transport of glucose into muscle cells (E) Increase in glucose transport in adipocytes Answer: D. Insulin decreases cell membrane permeability to both Na+ and K+ , but it decreases Na+ permeability more, causing hyperpolarization of skeletal and cardiac muscle cells and adipocytes but not liver or pancreatic cells. Insulin also promotes lipogenesis, protein anabolism, glycogenesis, and glycolysis. Insulin promotes glucose uptake by muscle adipose tissue and the liver, and it promotes storage and utilization of glucose in all three tissues. Glucose storage by muscle and liver is achieved by formation of glycogen via an in-crease in glycogen synthase activity. Glucose transport across skeletal and cardiac muscle cells and adip . . . . . . . . .