Thermoregulation

Animals stay warm or cool.

Some animals make their own heat. They stay warm in the cold.

Other animals use the sun. They sit in the sun to get warm. They can also find shade to stay cool.

Some animals have a body that stays the same. They make heat inside their bodies.

A dog can pant to stay cool. This helps them not get too hot.

Other animals change with the weather. They use the world around them. A lizard might lie on a hot rock. This helps it get warm.

If it gets too cold, some animals sleep. This helps them save energy. Bears do this when they sleep all winter.

It is good to stay at the right temperature. This helps all living things live well.

Living things must keep their bodies at the right temperature. This is called thermoregulation.

Some animals are endotherms. These are often called warm-blooded. They make their own heat through metabolic processes. This means they use food to make power. They have many mitochondria. These are tiny parts in cells that help make heat.

Other animals are ectotherms. People call them cold-blooded. They get heat from the world around them. They might sit in the sun to get warm. Or they might seek shade to cool down.

If a body gets too hot, it is called hyperthermia. If it gets too cold, it is called hypothermia.

Animals use many ways to stay safe. Mammals have fur to trap heat. Some have blubber, which is a thick layer of fat. This helps them stay warm in cold water. Birds use feathers to stay warm too. To cool down, many animals use evaporation. This is when water turns to gas. A dog pants to let heat out. A kangaroo might lick its arms to cool down.

Living things have a special way to stay safe. They must keep their body temperature within certain limits. This process is called thermoregulation.

It is part of something called homeostasis. Homeostasis is when a living thing keeps its internal conditions steady. This is very important even when the world outside changes. If a body gets too hot, it is called hyperthermia. If it gets too cold, it is called hypothermia.

Animals use different ways to manage their heat. Endotherms are often called warm-blooded. They make heat inside their bodies using metabolic processes. These animals have many mitochondria in their cells to help.

Ectotherms are often called cold-blooded. They use the world around them to change their temperature. They might lie in the sun to get warm. Or they might find shade to cool down.

Some animals even use dormancy to save energy. Bears hibernate and bats use torpor to drop their temperature.

Scientists have studied how this works for a long time. John Hunter observed the difference between these two groups. He saw that warm-blooded animals keep a constant temperature. He saw that cold-blooded animals change with their surroundings.

For a long time, we could not measure exact temperatures. This changed when thermometers were introduced. Now we know that different body parts have different temperatures. Scientists often check the rectum to find the core temperature.

There are many specific facts about how animals stay safe. Humans can face lethal heat if the wet-bulb temperature stays high. In 2022, studies showed heat above 30.55 °C is hard for healthy adults. Normal human temperature is about 37 °C.

To stay warm, mammals use fur or blubber. Blubber is a thick layer of fat found in whales. Birds use feathers to trap warm air. To cool down, many animals use evaporation. A dog pants to move water across its tongue. A kangaroo might lick its arms to cool.

Your own body uses a brain system to control heat. A part of the brain called the hypothalamus does this. It uses a signal to tell the body to change. In a hot place, it dilates skin blood vessels. This helps heat leave the body through the surface. In a cold place, it constricts those same vessels. This helps the body keep its heat inside.

This feedback loop keeps everything in a steady balance.

Thermoregulation is the biological process used by organisms to maintain a stable internal body temperature. This ability is vital because it allows life to persist even when the surrounding environment changes drastically. This process is a key part of homeostasis, which is the state of dynamic stability in an organism's internal conditions. Maintaining this stability is important because it keeps the body far from thermal equilibrium with its environment.

If an organism fails to regulate its heat, it can face dangerous conditions. Hyperthermia occurs when the body temperature rises significantly above normal levels. In humans, sustained wet-bulb temperatures can lead to lethal hyperthermia. Research from 2022 found that a wet-bulb temperature exceeding 30.55 °C causes uncompensable heat stress in healthy young adults. Conversely, hypothermia happens when the body loses heat faster than it can produce it, dropping the core temperature below normal.

Animals are often classified by how they manage this heat along a spectrum. Endotherms, often called warm-blooded, generate most of their heat through internal metabolic processes. These organisms can keep their internal temperature nearly independent of the outside air. They achieve this by having a larger number of mitochondria per cell, which allows them to metabolize fats and sugars at higher rates.

On the other end of the spectrum are ectotherms, commonly called cold-blooded. For these animals, internal physiological heat sources are of negligible importance. Instead, they rely heavily on environmental influences to regulate their temperature. Many ectotherms live in stable environments like the tropics or oceans. They use behavioral mechanisms, such as sun-bathing to increase heat or seeking shade to lower it.

Ectotherms use several specific methods to move heat in or out of their bodies. To gain heat, they might use conduction by lying on a hot surface or radiation by lying in the sun. They can also use convection by climbing to higher ground or entering warm air currents. To cool down, they may use evaporation through the loss of bodily fluids. They also use convection by increasing blood flow to body surfaces to maximize heat transfer. Another method is conduction, such as lying on cool ground or staying wet in a river.

Endotherms have developed complex structural and physiological adaptations to manage heat. To prevent heat gain in hot areas, many use evaporative cooling. Animals with sweat glands, like humans, release moisture through the skin. Animals with fur, such as dogs or pigs, rely more on panting to increase evaporation across the moist surfaces of the lungs and tongue.

Birds use a different method called gular fluttering, which involves rapid vibrations of the throat skin. To stay warm, mammals often use insulation. This can include fur or a thick layer of subcutaneous fat called blubber, which is common in marine mammals like whales.

Some animals even use dormancy to save energy, such as hibernating bears or bats in torpor.

Historically, our understanding of these thermal differences grew with technology. John Hunter observed that the main difference between warm-blooded and cold-blooded animals was the constancy of their temperature. Before the invention of thermometers, scientists could not obtain exact data on animal temperatures. Once thermometers were available, researchers discovered that heat production and loss vary across different body parts. Because blood circulation helps bring about a mean temperature, scientists must identify parts that most accurately reflect the internal organs. Traditionally, the rectum has been used to measure this core temperature, though in some species, the vagina, uterus, or bladder may be used.

The control center for this entire system is located in the brain. Thermoregulation is primarily managed by the preoptic area (POA) of the anterior hypothalamus. In mammals, specific neurons in the POA that express the prostaglandin E receptor 3 (EP3) are crucial. These neurons provide continuous inhibitory signals to other parts of the brain, such as the dorsomedial hypothalamus. In a hot environment, these inhibitory signals increase to suppress heat production and dilate skin blood vessels. In a cold environment, these signals are reduced to increase heat production and constrict blood vessels. This feedback loop ensures the body returns to its set point, a process that was fundamental to understanding mammalian homeostasis in 2022.

Thermoregulation connects to many broader biological concepts, including energy use and evolution. Maintaining a constant temperature is energetically expensive, which is why some animals use torpor to temporarily lower their metabolic rate. This strategy reduces the temperature difference between the animal and the air, minimizing heat loss. This also makes the process less costly in terms of energy. The study of these processes falls under the field of physiological ecology. By understanding how organisms balance heat, scientists can better understand how life survives in diverse global ecosystems.