Lesson 2 of 10 / Homeostasis and response
Controlling body temperature
Why do sweating and skin blood flow change together?
In this lesson: Explain how the hypothalamus coordinates responses to an increase or decrease in body temperature.
About 6 min
The key ideaThe hypothalamus coordinates changes in heat loss and heat production to oppose a change in body temperature.
Blue drops represent sweat; upward arrows represent heat removed during evaporation.
Red: skin blood flow. Blue: sweat. Vessel widths are schematic, not measured diameters.
Too warm: the hypothalamus coordinates more sweating and dilation of skin arterioles. Evaporation removes heat; greater surface blood flow increases heat transfer to cooler surroundings.
Explanation
Temperature receptors in the skin detect changes in the surroundings, while receptors in the hypothalamus detect changes in the temperature of blood flowing through it. The hypothalamus coordinates appropriate responses through the nervous system.
When the body is too warm, sweat glands secrete more sweat. Water evaporating from the skin takes heat from the body. Sweat that remains liquid provides much less of this cooling effect, so humid air can reduce the effectiveness of sweating.
Arterioles supplying the skin capillaries also dilate. More blood flows near the skin surface, allowing more heat to be transferred to cooler surroundings. The vessels change diameter; they do not move towards the surface.
When the body is too cold, these arterioles constrict, reducing blood flow near the surface and reducing heat loss. Sweating decreases. Rapid involuntary contractions of skeletal muscles cause shivering; increased respiration in these muscles releases more heat. These responses decrease as temperature returns towards its normal range.
Step by step
- 1
Detect
Temperature receptors provide information; the hypothalamus coordinates the response.
- 2
Change heat exchange
Link sweat evaporation and skin blood flow to the rate of heat loss.
- 3
Change heat production
In cold conditions, shivering increases muscle activity, respiration and heat release.
Worked example
Warm skin after exercise
Explain why a person may have warm, flushed skin while losing heat after exercise.
One way to explain it
Skin arterioles dilate, increasing blood flow through capillaries near the surface. More heat is transferred from the blood to cooler surroundings, helping temperature fall towards normal.
Why this answer works
- Warm skin does not mean the response is heating the body.
- Greater blood flow carries heat to the surface.
- State the corrective effect on internal temperature.
Is this true? "Capillaries move closer to the skin when the body is hot."
Blood vessels stay in place. Dilation of supplying arterioles increases the flow of blood through capillaries near the skin.