- Homeostasis is the process through which organisms regulate biological functions like heart rate, blood pressure, and temperature.
- Like a home heating system, homeostasis turns body functions on and off in response to feedback about an organism.
- This process allows an organism to operate freely and independently in the world.
Living things have a remarkable ability to function and thrive in a variety of environments that are constantly changing. Despite exposure to wildly different temperatures during heat waves and cold snaps, or even changes in rainfall and food availability, our bodies are able to keep a constant temperature, blood pressure, and electrolyte balance. How do animals keep doing this in the face of all the changing conditions around them? The answer lies in homeostasis.
Homeostasis is one of the big ideas in biology. The term, first coined in 1929 by American physiologist Walter Cannon, was meant to describe the regulation of our internal environment through feedback and feedforward systems.
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“Homeostasis is the sweet spot,” Muzlifah Haniffa, an immunologist at Newcastle University in England, tells Popular Mechanics. “And the process is to maintain it actively in that sweet spot and to return any deviation that occurs back to the sweet spot.”
It is often likened to a home’s heating system that kicks on the heater when the room temperature falls too low, and turns it off when the temperature gets high enough; in other words, the system turns on and off in response to feedback about the temperature of the room. Your body, it turns out, has similar systems in place that keep its biological functions maintained at set points. Levels of sodium and potassium levels in the blood, for example, are examples of nutrients that are homeostatically controlled. Some biological functions, like body temperature, are strictly maintained at a constant number. Others, like blood cortisol levels, may fluctuate between different set points based on stress levels or sleep cycles.
“Homeostasis describes how variables in the body are maintained in a relatively constant range, despite widely changing environmental conditions,” George Billman tells Popular Mechanics. Billman, a physiologist at Ohio State University, explains that homeostasis is what allows animals to be independent and interact in the world without disrupting their internal function.
An often-cited example is blood pressure. Throughout the day, blood pressure varies within a narrow range, which is important for keeping the blood supplied with a fresh batch of oxygen and nutrients. If the pressure is too low, then it cannot supply oxygen to the body’s tissues; if it is too high, it will damage the blood vessels. There are sensors in the blood vessels that monitor blood pressure and adjust the vessels accordingly. If an animal starts running, for example, its blood pressure will increase and deliver more oxygen and nutrients to the muscles, which need an extra boost. When the creature comes to a rest, the pressure comes back down.
“Something that’s alive tries to keep itself going, so we eat when we’re hungry, we drink when we’re thirsty,” Dr. Marc Basson, a physician and biological scientist at the University of North Dakota, tells Popular Mechanics.
Dr. Basson describes a scenario in which a person is busy during the workday and they forget to drink water and become dehydrated. The blood becomes more concentrated and the heart rate will jump up to make sure the smaller volume of blood gets distributed evenly throughout the body. Eventually, the brain will get the message and send a signal to drink. The person will become thirsty and get a glass of water, and eventually the blood volume will go up and the heart rate will come down. “When everything goes back to normal, that’s homeostasis,” he says.
“The best descriptor of homeostasis is stability,” William Cliff, a biologist at Niagara University in New York, tells Popular Mechanics. “It’s the idea that something’s in a relatively stable state, even though the environment around it may be changing.”
Cliff points out that the purpose of homeostasis is to allow organisms to operate freely and independently in the world. He says that organisms with more evolved homeostatic mechanisms generally have more independence than those with more primitive systems. Turtles, for instance, have a more pared-down version. In order to tolerate cold temperatures in the winter, they must bury themselves in the muddy bottoms of ponds. They can slow down their metabolism and live without food for months, surviving with very low levels of oxygen. But in their low-energy state, they cannot move about in the pond, reproduce, or carry out other basic life tasks.
“Homeostasis is not a condition for life. There are organisms that only regulate a certain few things, and they’re very successful,” Cliff says. But being better able to regulate our body functions can enable a freer and more independent life. “A polar bear living in the Arctic is independent of the thermal temperature around it. It can go on day after day doing the same thing whether it’s hot or cold,” he says. “The snake under those situations is not independent.”
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