In todays’ Time Machine, we are taking a look back at a paper written by Dr. Henry Gray Barbour during his time in the Department of Pharmacology at Yale University School of Medicine. Published in Physiological Reviews in 1921, his paper examined how body heat is regulated in various species.
In this review, Dr. Barbour explains that water is the best medium for conducting heat throughout the body. This is because water retains heat well, can be expelled through sweat to help cool the body, and circulates quickly to distribute heat, thereby preventing tissue damage.
Exploring how animals and humans regulate body temperature, Dr. Barbour highlights that while warm-blooded animals can regulate their internal temperature, doing so requires significant energy. The strategies animals use to regulate body temperature also vary from dogs panting and humans sweating to rabbits and elephants shifting blood flow to their large ears to dissipate excess heat to the environment. Adipose tissue also provides an important barrier to heat loss for organisms, resulting in lower metabolic demands to create heat. This means that a thin dog, for example, has a higher metabolism (and higher heat production) than a chunky dog.
In cold conditions, humans shiver to generate body heat and reduce blood flow to the skin to conserve heat. In warm environments, on the other hand, the body releases excess heat through dilated blood vessels near the skin that allow the body to radiate heat to the environment, and through sweat which cools the body by evaporation.
Body temperature is not constant and often fluctuates throughout the day. For diurnal species temperatures are typically lowest in the morning and highest in the afternoon or evening. For nocturnal animals, such as owls, peak body temperatures occur during the night instead. Internal and surface temperatures also vary throughout the body. You can measure this variation yourself using a surface thermometer.
The nervous system plays a key role in regulating body heat, which is why spinal cord injuries can impair a person’s ability to regulate body heat. The thyroid and adrenal glands also contribute to heat regulation through the release of hormones. These hormones are often down regulated in hibernating animals, allowing the animals to slow down their metabolism and reduce body temperature to conserve energy during a long winter fast. Conversely, increases in these hormones can raise metabolism and hence, heat production.
When an animal has a fever, the body’s internal thermostat resets to a higher temperature, prompting the body to retain heat that would normally be dissipated. This can increase the risk of dehydration and blood thickening, making it much harder to manage body temperature. Medications that reduce fevers work through various mechanisms – some dilate blood vessels to promote evaporative cooling, whereas anesthetics lower metabolism to reduce the production of heat.
About Dr. Barbour
Dr. Barbour completed his undergraduate studies at Trinity College in 1906 and earned his MD in 1911 from Johns Hopkins University. He began his professional career as an assistant professor of Pharmacology and Toxicology at Yale University from 1912-1921 after which he became professor and chair of pharmacology at McGill University (1921-1924), followed by the University of Louisville. He is best known for his research on temperature regulation and water balance as well as for coming up with a way to measure the specific gravity of blood plasma.
Sources
Henry G Barbour.The heat-regulating mechanism of the body. Physiological Reviews. 1(2): 295-326, 1921. DOI: 10.1152/physrev.1921.1.2.295
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Categories: Climate Change, Diet and Exercise, Environment, Exercise, Time Machine
Tags: American Physiological Society, climate, fitness, health, heat, history, medicine, metabolism, nursing, nutrition, Physiological Reviews, Sweat, temperature, thermoregulation, water balance, wellness
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