How Does the Body Regulate Temperature?
- Published8 Oct 2020
- Author Michael W. Richardson
- Source BrainFacts/SfN
When selecting an outfit for the day, you might turn to your phone, TV, or nearest window to check the weather. A 10-degree temperature shift could mean the difference between grabbing a light jacket or rolling up your sleeves on a nice day.
Your body is even more vigilant about regulating and tracking its internal temperature. Neuroscientist Shaun Morrison of Oregon Health & Science University explains how the body and brain regulate temperature, and what happens when things go awry.
How is the brain involved in temperature regulation?
Body temperature regulation is like a reflex. You’re not conscious of it. The average healthy human body maintains an internal temperature of around 37 degrees Celsius (98.5 degrees Fahrenheit), though individuals can vary slightly. The body makes tiny shifts and changes that keep it at a healthy temperature depending on the environment and the body’s output.
In the brain, the hypothalamus controls this reflex. It also plays roles in hormone secretion, sleep, and other functions. The hypothalamus receives input from temperature receptors in the skin and internal organs, including the gut.
Even at rest in a temperate environment, your hypothalamus remains vigilant. Muscles produce a huge amount of heat when they’re working, including the heart, guts, and even the diaphragm muscles that enable breathing. Maintaining a proper body temperature is a full-time job, even when it seems like you aren’t actively working any muscles.
When body temperature rises, what are the major risks?
The body’s cells are very susceptible to high temperatures. As temperature rises above 40 degrees Celsius (104 degrees Fahrenheit), the proteins in cells can start to unravel. This can impairs cell function and can eventually lead to cell death. In the brain, this can have long-term consequences, including permanent brain damage.
Reduced function of the heart muscle can be a real danger. As body temperature rises, the heart works harder to pump blood to the periphery to cool the body. As the heart muscle weakens, cardiac output falls and oxygen supply to the organs, including the brain, is reduced.
The biggest danger in a hot environment is dehydration and reduced blood flow to the brain. The moisture in sweat comes from water in the blood. If this water is not replenished by drinking, which could happen in a desert environment, then blood volume will decrease. This leads to reduced cardiac output and reduced blood flow to the brain.
When the heart suddenly slows, blood flow to other organs will also drop. If blood flow to the brain drops too much, victims of heatstroke will faint. This is an adaptive technique — it’s much easier for the heart to pump blood to the brain when you’re flat on the ground.
What happens when body temperature falls?
Falling body temperature is much less dangerous than rising temperature. While high temperatures can quickly cause cell death, low body temperature doesn’t have the same effect. That’s why some mammals can enter periods of hibernation where their internal temperatures drop significantly. While bears’ internal temperatures may only drop a few degrees during their slumber, the Arctic ground squirrel’s temperature can drop close to freezing, though only for a few weeks. Humans don’t have that ability, hypothermia sets in well before then.
In low temperatures, cellular function begins to slow. Humans may become confused or disoriented. Those are signs that neurons in the cerebrum or cerebral cortex aren’t sending signals as they should. But the main danger isn’t cognition. Like heatstroke, hypothermia’s threat lies in the heart and the brain areas regulating it. As internal temperature drops to dangerous levels, heartbeat regulation degrades. Victims develop arrhythmias — irregular heartbeats that alter blood flow to the rest of the body. If blood isn’t pumped to key organs, especially the brain, then you’re in trouble. Cardiac arrhythmias leading to cardiac arrest seem to be what kills most people who die of exposure.
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