Thermoregulation

Thermoregulation is the way living things keep their body temperature just right, even when it's very hot or very cold outside. This helps them stay healthy and work properly. Some animals, called thermoconforming organisms, just let their body temperature match the air around them. But most animals, including humans, have special ways to control their temperature inside their bodies.

When the body gets too hot, it can lead to a condition called hyperthermia, which can be very dangerous. For humans, this can happen if the air stays very hot for too long. The opposite problem is hypothermia, when the body gets too cold. This usually happens after being outside in cold weather for a long time. Both of these conditions are serious and need care to bring the body back to a normal temperature.

Scientists didn’t know exactly how animals’ temperatures worked until they invented thermometers. These tools helped them learn that different parts of the body can have different temperatures. They found that some places, like deep inside the body, show the most accurate picture of how warm or cool a person or animal really is. Some animals, like bears and bats, can even let their body temperature drop for short periods to save energy.

Classification of animals by thermal characteristics

Endothermy vs. ectothermy

Animals can keep their body temperature steady in different ways. Endotherms, often called warm-blooded animals, make most of their heat through their own body processes. They can keep their temperature steady even when it's cold outside by creating more heat inside. These animals have more energy-making parts in their cells, which helps them produce heat.

Ectotherms, sometimes called cold-blooded animals, rely on outside sources like the sun or warm surfaces to control their temperature. Even though we call them cold-blooded, their temperatures can be similar to warm-blooded animals. They live in places where the temperature stays steady, like tropical areas or oceans, and change their behavior to manage temperature—like basking in the sun or hiding in the shade.

Ectotherms

Main article: Ectotherm

Ectothermic cooling

Ectotherms cool down in several ways:

• Vaporization: Losing water through sweat or other body fluids.
• Convection: Increasing blood flow to the skin to release heat.
• Conduction: Losing heat by touching cooler surfaces, like lying on cool ground or staying in water.
• Radiation: Releasing heat by sending it away from the body.

Ectothermic heating (or minimizing heat loss)

Ectotherms warm up or keep heat loss low by:

• Convection: Moving to warmer places, like climbing trees or entering warm water.
• Conduction: Lying on hot surfaces.
• Radiation: Basking in the sun or adjusting body position to catch more sunlight.
• Insulation: Changing body shape or inflating to keep in heat.

Some fish can stay active in very cold water by using special substances to prevent ice from forming in their bodies. Amphibians and reptiles cool down by losing water and by changing their behavior, like lying on a warm rock to absorb heat.

Endothermy

Main article: Endotherm

Endotherms control their own body temperature, often keeping it steady. They cool down by losing water through breathing or sweating. Animals with fur, like cats and dogs, mainly pant to lose heat through their mouths and tongues since they don’t sweat much except on their paws. Birds can cool down by rapidly moving their throat skin. Feathers and fur act as insulators to keep heat in. Some animals, like polar bears, have thick layers of fat called blubber to stay warm.

In cold weather, some animals lower their metabolism to reduce heat loss and save energy. Many can lower their body temperature temporarily at night to survive cold temperatures. They use many ways to control temperature, including behaviors, body changes, and a system that senses and responds to temperature changes to keep everything balanced.

Homeothermy compared with poikilothermy

Homeothermy and poikilothermy describe how steady an animal's internal temperature is. Most endothermic animals, like mammals, are homeothermic, keeping a steady temperature. Some animals can switch between temperature control methods and are poikilothermic, meaning their temperature can change a lot. Most fish are ectotherms and poikilothermic, relying on the water around them for heat.

Vertebrates

John Hunter showed that warm-blooded animals, like birds and mammals, keep a steady body temperature, while cold-blooded animals change with their surroundings. Birds and mammals usually stay warm no matter the weather around them, a trait called homeothermy. Other animals often change their temperature with the environment, known as poikilothermy.

Birds and mammals have special ways to stay warm or cool. In cold places, they might stand up their feathers or hair to trap heat, grow larger, store fat for energy, or use special blood flow to keep warm. In hot places, they might stay in cooler spots, sweat or pant to cool down, or have longer body parts to send heat away. Humans, like other mammals, also regulate their temperature through their brain and can adapt to many different climates. Reptiles, such as certain lizards, move to different spots to stay at their needed temperature.

In plants

Some plants can warm themselves up, which helps them grow even in cold weather. For example, flowers in the Araceae family and cycad cones can make heat. The sacred lotus stays warmer than the air around it when it blooms, using stored energy from its roots.

Plants might warm up to protect themselves from frost or to attract insects that help them reproduce. Certain plants, like wheat and potatoes, have special proteins that prevent freezing.

Behavioral temperature regulation

Animals, including those that are not humans, have ways to keep their body temperature just right. For example, desert lizards cannot control their own temperature, so they move to warmer or cooler spots to stay comfortable. In the morning, they might come out of their burrows and sit in the sun to warm up. They can also warm up by touching hot rocks. To cool down, they might lift their feet off hot sand, find shade, or go back into their burrows.

Some animals share warmth with each other, like bats and birds that huddle together to stay warm. Others, like koalas, choose cooler parts of trees to stay comfortable on hot days. Some animals even go into a deep sleep called hibernation during cold weather to save energy, while others enter a similar state called estivation during very hot weather. Small animals like bats and hummingbirds may also take short naps called torpor to save energy each day.

Variation in animals

Living things have different ways of keeping their body temperature just right, even when it's very hot or very cold outside. Some animals, like humans, work hard to stay at a steady temperature. Others, like some lizards, just take on the temperature of where they are.

For humans, a normal temperature is around 36.8 °C or 98.2 °F, but this can change a little bit from person to person. The temperature can also change during the day. It’s usually lowest while we’re sleeping and highest during the day when we’re active.

Effect on lifespan

It is hard to study how changes in body temperature affect how long humans live.

Limits compatible with life

Animals can only live within certain temperature ranges. If it gets too cold, an animal’s body processes slow down. This can affect the brain and make the animal very sleepy. Eventually, without help, the body can stop working.

If it gets too hot, the body’s processes speed up too much, and the body can run out of energy. This can also affect the brain and make the animal confused or lose consciousness. Some animals can handle very high temperatures, like certain desert ants and mites, which can survive in extreme heat.