No matter the weather, the human body stays within a very small range of temperatures. This is because the body regulates the temperature, allowing a precise range to keep the body alive and working properly. The process actually starts at the hypothalamus in the brain. The hypothalamus contains the temperature sensors, as well as the control mechanisms to adjust internal temperatures based on the feedback it receives. The normal range for a human body is 37-37.8 degrees Celsius (98-100 degrees Fahrenheit). This range is considered homeostasis, a stable condition for the body.
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There are many different factors that can influence the body's temperature. These include illness, infections, outside temperatures, as well as drug and alcohol use. The hypothalamus senses these changes, and tells the body if it needs to start or stop sweating, create bumps and raise arm or leg hairs to hold in more heat, cause shivering, add certain hormones to the body to increase heat, increase or decrease metabolism, and even alter the width of capillaries in order to control blood flow.
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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:
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.
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.
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.
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.
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.
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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.
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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.
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.
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The four mechanisms are summarized as convection, radiation, conduction, and evaporation. More specifically they include: evaporation of sweat, conduction of heat from the body's core to the surface, radiation of heat away from the body, and convection by the heart pumping blood throughout the body.
The muscles in the body are constantly producing heat. These include the heart, diaphragm, and digestive systems. The outside environment, temperature of food consumed, and illness also affect body temperature.
When the body cannot maintain homeostasis for temperature, it is considered thermoregulatory dysfunction. This can include a fever, heatstroke, frostbite, or other temperature related illnesses.
When the body constricts the veins close to the skin in order to prevent heat loss. That is one type of temperature regulation. Another example, is when the body sweats to help cool the body down.
To regulate something means to maintain it within stable parameters. In the human body, the hypothalamus is responsible for regulating body temperature.
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