**Question:** True about glucagon

A. Glucagon is primarily involved in increasing blood glucose levels.
B. Glucagon is secreted in response to high blood glucose levels.
C. Glucagon has no effect on blood glucose levels.
D. Glucagon secretion is regulated by insulin.

**Correct Answer:**

**Core Concept:** Glucagon is a peptide hormone produced by alpha cells in the pancreas, which plays a crucial role in maintaining glucose homeostasis.

**Why the Correct Answer is Right:**
Glucagon acts as a counterregulatory hormone to insulin, released in response to low blood glucose levels (hypoglycemia) to increase glucose production in the liver and promote glucose uptake in peripheral tissues.

**Why Each Wrong Option is Incorrect:**

A. **Glucagon primarily increases blood glucose levels**: This is incorrect because glucagon actually lowers blood glucose levels by stimulating glycogenolysis, gluconeogenesis, and lipolysis, leading to increased glucose production and release.

B. **Glucagon is secreted in response to high blood glucose levels**: This is incorrect because glucagon is actually released in response to low blood glucose levels (hypoglycemia) to counteract the actions of insulin and raise blood glucose levels.

C. **Glucagon has no effect on blood glucose levels**: This is incorrect because glucagon does indeed lower blood glucose levels by stimulating hepatic glucose production.

D. **Glucagon secretion is regulated by insulin**: This is incorrect because glucagon secretion is regulated by the counterregulatory hormones, such as cortisol, epinephrine, and growth hormone, in response to hypoglycemia. Insulin does not directly regulate glucagon secretion.

**Clinical Pearl:** A thorough understanding of the counterregulatory hormones and their role in maintaining glucose homeostasis is essential in managing hypoglycemia and understanding the pathogenesis of diabetes mellitus.

In clinical scenarios, a patient's blood glucose level should be assessed before administering glucagon, as incorrect use of glucagon can cause a sudden rise in blood glucose levels, which may worsen hypoglycemic symptoms and complications.