Re: How (and mostly why) does temperature affect the heart rate?

Hello Marlo,

Thanks for submitting the interesting question. As you probably already know, the body has to regulate the systems to keep us healthy (and alive!) Temperature is just one of those systems that is controlled by the autonomic nervous system, interacting with an area of the brain called the hypothalamus.

The body's goal is to maintain a very narrow range of temperature for the organs and tissues - this is "measured" by the body in a central location at that hypothalamus.

In your question, you wondered why the body would not try to warm itself by increasing blood flow to the skin. Well, in order to make that helpful, the outdoor temperature would need to be quite high - if you think about normal room temperature, it is at least 20-25 F lower than normal body temperature. So pushing blood to the skin would actually cool it, not warm it.

Also, the body does not have to rely on increasing the heart rate to push more blood to the skin - the body signals to small blood vessels in the skin to increase/decrease in diameter, allowing more/less blood to flow. The rest of the circulatory system compensates in a variety of ways. It's not quite as simple as just heart rate changing.

Hope this helps. There is a very good review of thermoregulation at this site: http://www.faqs.org/sports-science/Sp-Tw/Thermoregulatory-System.html that you might find helpful.

Best wishes.