Describe, step-by-step, how an increase in blood glucose (i.e. caused by eating
ID: 78667 • Letter: D
Question
Describe, step-by-step, how an increase in blood glucose (i.e. caused by eating a bowl of sugary cereal such as Cap'n Crunch) would result in changes in the hormones insulin and glucagon during or within 15 minutes after the meal was consumed compared to 1 hour after the meal was consumed. Be specific in your answer & include brief description of: a) Where the hormones insulin & glucagon are made vs. where they act in the body related to regulation of blood glucose b) How the 2 hormones differ in their relative level and action both during the meal vs. 1 hour after mealExplanation / Answer
a) Insulin is produced by the beta cells of pancreas and glucagon is secreted by alpha cells. These alpha and beta cells along with delta cells which secrete somatostatin constitute the Islet of Langerhans or the endocrine part of pancreas. Both, Insulin and glucagon are involved in regulation of glucose levels in blood. Insulin decreses and glucagon increases blood glucose levels. They act on peripheral tissues and target organs through receptors and regulate carbohydrate, fat and protein metabolism.
b) Insulin release is biphasic. A very rapid rise in insulin secretion is seen within minutes after administration of a glucose load followed by a rapid fall and then if the glucose overload is still present, a long lasting slow release of the insulin is seen. The first top results from exocytosis of granules from the "readily released" pool and comprises 5-10% of the insulin stored in the beta cells. The sustained slow release is comprised of granules from the "reserve pool". Closer examination of this phenomenon has greatly increased knowledge about insulin secretion. Let us examine these steps closely.
1: Fast first phase occurs due to exocytosis of already stored granules and comprises 5-10% of insulin stored in beta cells of pancreas. It takes place during the meal.
2: A slow second phase requires ATP. Granules are moved from the reserve pool to the readily released pool of insulin granules. Docking and energizing of the granules are part of this slow second phase. This slow phase is the major contributor to insulin release. Maximal quantities of insulin are released after 1 hour.
Glucagon secretion is not as well understood as that of insulin. Glucagon secretion is linked to the alpha cell's metabolism. Hypoglycemia and anoxia lead to release of glucagon from these cells. Alpha cells release glucagon in response to metabolic stress.