**Question:** The first physiological response to high environmental temperature is

A. Increased heart rate
B. Increased blood volume
C. Increased skin blood flow
D. Diuresis

**Core Concept:** The human body has various physiological mechanisms to maintain its core temperature in response to environmental changes. When the environment becomes hotter, the body initiates compensatory responses to dissipate heat and prevent overheating.

**Why the Correct Answer is Right:** The correct answer, C. Increased skin blood flow, is the initial response to high environmental temperature. This response helps to evaporate sweat, which cools the skin surface and, in turn, the entire body.

**Why Each Wrong Option is Incorrect:**

A. Increased heart rate (Option A) is a later response, as it contributes to more efficient heat generation and distribution within the body.
B. Increased blood volume (Option B) is not the primary response to high temperature. Its primary role is to increase cardiac output, which helps maintain tissue perfusion in hypothermia.
D. Diuresis (Option D) is a response to dehydration, not high temperature. It involves the production and excretion of more urine, helping to flush excess electrolytes and water from the body.

**Clinical Pearl / High-Yield Fact:** The sequence of responses to high temperature is as follows:
1. Increased skin blood flow (C)
2. Increased heart rate (A)
3. Vasodilation (D)
4. Diaphoresis (D)
5. Shivering (A)
6. Alarm phase (fever response)

**Correct Answer: C.** Increased skin blood flow is the correct answer because it directly addresses the objective of dissipating heat through increased heat exchange with the surroundings. This is achieved through increased blood flow to the skin, promoting sweating and evaporative cooling.