Body Temperature Regulation & Homeostasis

Thermoregulation in Humans

Thermoregulation is the process of regulating one's own body temperature. The body first must sense current temperatures and conditions in order to respond to changes. There are temperature receptors on the skin, around veins, and in the spinal cord area. They send the message to the brain, specifically the hypothalamus, about current inputs. Regulating the body's temperature to such a small range is difficult work. Even if a body is resting in an ideal temperature location, muscles continue producing heat. The heart still beats, the digestive system still processes food and nutrients, and the diaphragm allows breathing to continue. Each of these internal processes produces heat. When people actively use additional muscles or change their environment, there is even more to be compensated for. As data is sent to the hypothalamus, it tells the body how to respond in order to maintain homeostasis.

There are two general possibilities for the hypothalamus to restore homeostasis: heat up the body, or cool down the body. The body heats up through a variety of processes:

• Shivering and increased muscle activity - This converts stored chemical energy in order to raise heat levels in the body.
• Piloerection - This forces the body hairs to contract and stand on end. This allows the heat given off by the body to be trapped closer, and reduces heat loss. While human arm and leg hairs are often thin and this doesn't provide much benefit, this same system is seen in other mammals much more effectively. In humans, this is likely a leftover response from our evolutionary ancestors.
• Vasoconstriction - This narrows the blood vessels close to the skin so that the heat given off decreases.
• Thyroxin - This hormone comes from the thyroid and raises a person's metabolic rate. This conversion of chemical energy helps create internal heat.

The body must also cool itself in the case of getting too hot. Some of these same processes are reversed, while others are completely different.

• Sweating - This helps to cool the body by releasing water and salt.
• Vasodilation - This dilates or opens up the veins wider. This allows increased blood flow near the surface of the skin, transferring more of the internal heat to external sources.
• Stopping piloerection and thyroxin - Telling the body to have body hairs lay naturally flat and not increasing the metabolism both help cool the body to a certain extent.

Homeostasis in Humans

Homeostasis is the stable, ideal condition of the body. This is achieved at a range of 37-37.8 degrees Celsius (98-100 degrees Fahrenheit). The process of achieving homeostasis is fluid and constantly adjusting. For example, as a person gets colder, they may develop shivers but not piloerection, or they may experience vasoconstriction, but not thyroxin. If the person responds by adding layers of clothing, turning up the air temperature or moving to a warmer location, immediate adjustments can be made to the body's response.

Endotherms

Birds, humans, and other mammals are considered endotherms. An endotherm is a type of animal that uses internal processes to maintain body temperature. Endotherms are also known as warm-blooded animals. Endotherms maintain a high metabolic rate by burning many calories, in order to maintain a body temperature higher than the surrounding air.

Ectotherms

Amphibians, reptiles, fish, and invertebrates are considered ectotherms. An ectotherm is a type of animal that relies on external processes to maintain body temperature. These animals typically warm their bodies with sunlight or a heat lamp. Ectotherms are also known as cold-blooded animals.

Thermoregulatory Dysfunction

There are times when the body gets out of homeostasis, and if it stays that way for very long it can cause serious health conditions and even death. Having a temperature out of homeostasis for more than a few minutes is called thermoregulatory dysfunction.

Excess body heat

A fever is a sign of illness that should be monitored and treated if it becomes too high.

If body temperature goes above 40 degrees Celsius (104 degrees Fahrenheit), cell proteins start to unravel. This impacts cell function and can lead to cell death. This can even cause permanent brain damage. Reduced function of the heart muscle is obviously concerning. With increased temperatures, the heart must work harder to move blood and cool the body. If the heart weakens, blood movement slows and the amount of oxygen being supplied throughout the body is reduced. The lack of oxygen can prevent organs, including the brain, from functioning properly. Another concern is dehydration. As the body sweats to cool off the body, the water is coming out of the blood. If this water isn't replenished by drinking, the volume of blood in the body decreases. This also reduces blood flow throughout the body. When the heart rate suddenly drops, heatstroke is likely. Heatstroke causes a person to faint. This is because it is easier for the heart to pump if the person is flat rather than standing. The body is doing everything it can to get back to homeostasis.

Insufficient Body Heat

The human body can withstand freezing, or almost freezing temperatures for longer than it can handle being too hot.

Lower body temperature is not as dangerous as a high body temperature. In fact many mammals have adapted to internal temperature drops by entering a period of hibernation. Humans lack this ability and hypothermia is a concern. With decreased temperature, cellular functions slow. People can become disoriented or confused. The real danger comes from the heart. With lower temperatures, heartbeat regulation decreases. Irregular heartbeats, known as arrhythmias, alter blood flow throughout the body. Without enough blood going to the brain, many other processes slow and stop. Most people who die of being too cold actually die from cardiac arrest caused by an arrhythmia.

Lesson Summary

The process of maintaining a stable body temperature is called thermoregulation. This is controlled by the hypothalamus, a specific area in the brain. It takes in temperature readings from throughout the body, and constantly adjusts many processes in the body to maintain a stable temperature, considered homeostasis. It can tell the body to release more internal heat in order to cool down the body. This often appears as sweating or moving the heat from internal organs to the skin, so it can be released in the air. The hypothalamus can also tell the body to retain more heat by increasing muscle movement, such as shivering, and constricting the veins near the skin to prevent heat loss. Thermoregulatory dysfunction is when the body's homeostasis is not being maintained. This is very quickly concerning if the body becomes too hot. It can cause heatstroke, and permanent brain damage. While being too cold is also concerning, this process takes much longer to lead to serious complications. Both being too hot and too cold can cause the heart to stop functioning properly, limit the blood supply to the brain, and be a cause of death.

Humans are considered endotherms because they use internal processes to regulate body temperature. Endotherms are also known as being warm-blooded, such as birds and mammals. Reptiles, amphibians, and other animals are considered ectotherms as they rely on external factors to provide warmth. They are often known as being cold-blooded.