**Question:** Stimulus for insulin secretion is-

A. Increased blood glucose concentration
B. Decreased blood glucose concentration
C. Infusion of glucagon
D. Infusion of somatostatin

**Core Concept:** Insulin and glucagon are the two primary hormones involved in maintaining glucose homeostasis in the body. They are secreted by the alpha and beta cells of the pancreas, respectively. Insulin promotes glucose uptake and storage in target cells, while glucagon stimulates glycogenolysis and gluconeogenesis in the liver to increase blood glucose levels.

**Why the Correct Answer is Right:** The correct answer, A, "Increased blood glucose concentration," highlights the main stimulus for insulin secretion. When blood glucose levels rise, the beta cells of the pancreas detect the increase in blood glucose and secrete insulin to facilitate glucose uptake by cells, thereby decreasing blood glucose levels.

**Why Each Wrong Option is Incorrect:**

B. Decreased blood glucose concentration (incorrect): Although hypoglycemia can lead to glucagon secretion, it is not the stimulus for insulin secretion. Insulin secretion is primarily triggered by hyperglycemia (high blood glucose levels).

C. Infusion of glucagon (incorrect): Infusion of glucagon would result in increased blood glucose levels, counteracting the expected effect of insulin secretion. Glucagon is secreted when blood glucose levels are high to counteract it, not stimulate insulin secretion.

D. Infusion of somatostatin (incorrect): Somatostatin is a hormone that inhibits the secretion of various gastrointestinal peptides, including insulin and glucagon. Infusion of somatostatin would not stimulate insulin secretion but rather suppress it, making it the wrong answer.

**Clinical Pearl:** The understanding of insulin and glucagon secretion helps healthcare professionals manage patients with diabetes mellitus, particularly type 1 diabetes, where the body does not produce insulin, leading to high blood glucose levels, and patients need exogenous insulin therapy to maintain euglycemia. Clinicians must also consider the differential diagnosis of hypoglycemia (low blood glucose) and its potential causes, such as adrenaline overdose, starvation, or excessive insulin administration.