## Core Concept
The body's response to hypoglycemia involves a complex interplay of hormonal and neural mechanisms aimed at rapidly restoring normal blood glucose levels. The primary goal is to counteract the effects of low blood glucose on the brain and other tissues. The initial response to hypoglycemia is crucial for preventing severe neurological damage.

## Why the Correct Answer is Right
The correct answer, **C. Glucagon**, is part of the body's immediate response to hypoglycemia. When blood glucose levels drop, the pancreas releases glucagon, a hormone that stimulates the liver to convert stored glycogen into glucose and release it into the bloodstream. This rapid response is vital for quickly correcting hypoglycemia. Glucagon works by activating **glycogen phosphorylase** and inhibiting **glycogen synthase**, thus promoting glycogenolysis and inhibiting glycogenesis.

## Why Each Wrong Option is Incorrect
- **Option A:** While **epinephrine (adrenaline)** is indeed released in response to hypoglycemia and helps to increase glucose levels by stimulating glycogenolysis and gluconeogenesis, it is not the first line or the most direct response in terms of rapidity and specificity for correcting blood glucose levels.
- **Option B:** **Cortisol** does play a role in glucose metabolism by promoting gluconeogenesis and inhibiting glucose uptake in peripheral tissues, but it is not the immediate response to hypoglycemia. Cortisol levels increase more slowly and its effects are more sustained.
- **Option D:** **Insulin** is actually the hormone that lowers blood glucose levels, making it worsen hypoglycemia. It is not a response to hypoglycemia but rather the cause of hypoglycemia when in excess.

## Clinical Pearl / High-Yield Fact
A key clinical pearl is that the initial management of hypoglycemia involves administering **glucose** (or glucagon if the patient is unable to take glucose orally). Glucagon is particularly useful in situations where the patient is unconscious or unable to consume glucose orally. Remember, "glucagon" for hypoglycemia when you can't give glucose!

## Correct Answer: C. Glucagon.