Exercise in the heat and cardiovascular drift

Overview

The hypothalamus and thermoreceptors, radiation, conduction, convection and evaporation, humidity, sweating and falling plasma volume, venous return and stroke volume, cardiovascular drift and how to reduce it, and early-morning marathons.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   Which part of the brain controls body temperature?

   Model answer

   The hypothalamus is the body's thermoregulatory centre. The hypothalamus receives information from thermoreceptors and triggers heat loss or heat gain.

2. 2

   Where are the thermoreceptors that detect body temperature found?

   Model answer

   Peripheral thermoreceptors are found in the skin. Central thermoreceptors in the hypothalamus monitor the temperature of the blood.

3. 3

   How does the body lose heat when core temperature rises during exercise?

   Model answer

   Arterioles supplying the skin vasodilate, bringing warm blood to the surface. Sweat glands increase sweat production so heat is lost by evaporation.

4. 4

   Name the four ways the body loses heat.

   Model answer

   The body loses heat by conduction, convection, radiation and evaporation.

5. 5

   Which method of heat loss matters most during exercise in the heat, and why?

   Model answer

   Evaporation of sweat is the main method during exercise in the heat. Radiation and convection fail when the air is as hot as the skin.

6. 6

   Why is exercise in hot, humid conditions especially demanding?

   Model answer

   Humid air is already heavily loaded with water vapour, so sweat evaporates poorly. Heat is not lost effectively, so core temperature keeps rising.

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