Homeostasis refers to the ability of an organism or environment to maintain a state of internal balance and physical wellbeing in spite of changes or outside factors. Successful homeostasis is vital to the survival of any living thing, and being able to maintain homeostasis even in adverse conditions is one of the most important evolutionary advantages.
Here are some homeostasis examples, beginning with the human body, then moving on to examples in animals and plants.
The human body is an amazingly complex machine, but many of its parts and processes exist simply to maintain homeostasis. That is, the machine exists so the machine can continue to exist.
- Humans' internal body temperature is a great example of homeostasis. When someone is healthy, their body maintains a temperature close to 98.6 degrees Fahrenheit (37 degrees Celsius). Being warm-blooded creatures, humans can increase or decrease temperature internally to keep it at a desirable level. Whether you're lying in the summer sun or playing in the winter snow, your body temperature only changes by a degree or two. That's an example of homeostasis being maintained. When you get shivery in the cold, or sweat in the summer, that's your body trying to maintain homeostasis.
- Glucose is the most basic form of sugar, and the only type the body can use directly. The body must maintain proper glucose levels to ensure a person remains healthy. When glucose levels get too high, the pancreas releases a hormone known as insulin. If blood glucose levels drop too low, the liver converts glycogen in the blood to glucose again, raising the levels.
- When bacteria or viruses that can make you ill get into your body, your lymphatic system kicks in to help maintain homeostasis. It works to fight the infection before it has the opportunity to make you sick, ensuring that you remain healthy.
- The maintenance of healthy blood pressure is an example of homeostasis. The heart can sense changes in blood pressure, sending signals to the brain, which then sends appropriate instructions back to the heart. If blood pressure is too high, the heart should slow down; if it is too low, the heart should speed up.
- More than half of a human's body weight percentage is water, and maintaining the correct balance of water is an example of homeostasis. Cells that have too much water bloat and can even blow up. Cells with too little water can end up shrinking. Your body (and a healthy intake of fluids) maintains a proper water balance so that neither of these situations occurs.
- Calcium levels in the blood must be maintained at proper levels. The body regulates those levels in an example of homeostasis. When levels decrease, the parathyroid releases hormones. If calcium levels become too high, the thyroid helps out by fixing calcium in the bones and lowering blood calcium levels.
- The nervous system helps keep homeostasis in breathing patterns. Because breathing is mostly involuntary, the nervous system ensures that the body is getting much needed oxygen through breathing the appropriate amount of oxygen.
- Eating, drinking, even simple breathing can introduce indigestible and even dangerous substances into the body. The body maintains homeostasis by eliminating these substances through the urinary and digestive systems. An individual simply urinates and defecates the toxins and other nasty things from the blood, restoring homeostasis to the human body.
You can find examples of homeostasis through the animal kingdom, from fish drinking water to animals seeking salt licks!
- Did you know that many of your pets' behaviors are meant to maintain homeostasis? When your dog hangs his tongue out and pants, for example, he's basically sweating, bringing his body temperature down. Does your cat like to sleep in sunbeams? Same deal, only your cat is trying to get warmer. It's all about maintaining that homeostasis.
- Homeostasis is everything in cold-blooded animals. Lacking the ability to control their own body temperature, reptiles, amphibians and fish go to amazing lengths to find the right climate. The African lungfish, for example, estivates. When summer comes around, lungfish wrap themselves in a ball of mud and mucus and sleep the heat away, coming out months later when things have cooled off.
- Body temperature isn't the only component of homeostasis. There's also the microbiome, bacteria and other organisms that grow inside animals and keep them healthy. To get and keep those microorganisms, young animals from koalas to elephants will eat the feces of their parents. Thankfully, we humans are born with the proper bugs.
- Salt licks are another example of animals maintaining homeostasis. When their diet doesn't provide certain necessary minerals, animals like moose and woodchucks will seek out and lick rocks and other objects that contain those minerals. That's been going on for millions of years. Just look at Big Bone Lick State Park in Kentucky. They had mammoths at their salt lick!
- Ever wonder whether fish drink water? They do! Keeping up your water levels is a vital homeostatic process. Freshwater fish take in water through their gills, while saltwater fish drink through the mouth. To avoid salt overdose, saltwater fish have special cells that pump salt out of their bodies.
Humans and animals aren't the only ones who rely on homeostasis. Plants need to maintain the same balance in order to survive and thrive too.
- Like animals, plants also "breathe," though the exchange is the reverse of what we do. Plants take in carbon dioxide and release oxygen. Did you know they also regulate how much they take in and let out? Leaves have stomata, holes on the underside, that expand and contract to get just the right combination. That's homeostasis.
- Leaves are machines for maintaining homeostasis. In addition to the process of photosynthesis described above, those same stomata take in and excrete nutrients, including salt and many others, based on whether the plant needs more or less.
- Stomata are a triple threat. They regulate photosynthesis and plant nutrition, but they also maintain a plant at the optimum water level. When stomata open wide, they dry the plant out. When they close, they help retain water.
- Plants go to great lengths to maintain the proper temperature too. Being less mobile than the average animal, plants have to get creative. Sunflowers, for example, got their name for a reason: they're heliotropes, following the sun across the sky to maximize photosynthesis. Plants also undergo gravitropism, using gravity to guide their growth. Roots have evolved to go towards gravitational pull, while shoots shoot up against it.
- Plants have beneficial bacteria in their system just like animals. There's a whole category of microorganisms called PGPR, or "plant-growth promoting rhizobacteria." The bacteria occurs in soil and likes to hang out in roots. In fact, they like it so much, they pay rent: PGPR fend off other microbes that cause disease and help plants use minerals and make important hormones.
Homeostasis is universal. In fact, many biologists describe the whole natural world as maintaining homeostasis, responding to changing climate and species diversity to keep planet Earth in the most livable possible state.
At a more personal level, homeostasis is simply a word for living things ordering their bodies in order to continue living. Illness disrupts homeostasis, and health is largely defined by how well an organism maintains homeostatic balance.
If you want to continue your journey through the human body, you can get deep into proteins, its fundamental building blocks. Alternatively, you could go big and read up on macroevolution for examples of massive systems maintaining their own homeostasis on a species-wide scale.