Skin and Heat Regulation: All mammals are warm-blooded animals and can regulate and maintain constant internal body temperature. This mechanism of regulating and maintaining constant body temperature is known as thermoregulation. The hypothalamus is a region of the brain responsible for controlling body temperature.

When it detects a reduction or rise in internal temperature, it transmits messages to the muscles, organs, glands, and neurological system. It reacts in a number of ways to help the body regain control of its temperature. Let’s learn more about Skin and Heat Regulation, its functions, factors and mechanism.

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Skin and Heat Regulation: Overview 

All mammals including humans are warm-blooded endothermal or ectothermal. Their body temperature fluctuates with the environmental temperature. This means that they must somewhere escape both conditions too hot or too cold environment and thus they hibernate (winter sleep) or aestivate( summer sleep). The temperature of a healthy body falls within a small range. A person’s normal body temperature is between 98°F (37°C) and 100°F (37.8°C). When it comes to temperature, our body is quite adaptable. However, if our body temperature reaches elevated levels, it can impair our ability to function. For example, “hypothermia” occurs when our body temperature dips below 95°F (35°C). This illness has the potential to cause cardiac arrest, brain injury, and death. You can suffer brain damage or even death if your body temperature climbs to 107.6°F (42 °C).

Many factors, such as spending time in cold or hot weather, might change your body’s temperature.

Internal temperature can be raised by a variety of factors, including:

1. Fever
2. Exercise
3. Digestion

Internal temperature can be lowered by a variety of factors, including:

1. Drug use
2. Alcohol use
3. Metabolic conditions, such as an under-functioning thyroid gland

Fig: Skin

Arrector Pili Muscles

Fig: Arrector Pili

1. The skin’s hairs lie flat, preventing heat from being trapped between the hairs by a layer of still air. 
2. The arrector pili muscles, which are microscopic muscles beneath the skin’s surface, are responsible.
3. The connected hair follicles are not erect when these muscles relax. 
4. These flat hairs accelerate the flow of air adjacent to the skin, increasing convectional heat loss.

Heat Production

In the human body, there are numerous sources of heat production.

1. Chemical reactions involving the oxidation of glucose in all body cells, particularly in the liver, release heat.
2. The activity of our muscles generates the majority of the heat produced in our bodies. On a cold day, vigorous movement keeps you warm; on a hot day, it overheats you.
3. Consumption of hot meals and beverages produces a moderate amount of heat.

Ectothermal and Endothermal

The terms cold-blooded and warm-blooded have been substituted by poikilothermal (Poikilo: varying) and homeothermal (Homeo: same) respectively. The terms ectothermal (ecto: outside) and endothermal (endo: inside) are used for animals according to the manner in which they warm their bodies. Mammals and birds have an internal heat producing mechanism (endothermal). The Body temperature of other animals rises or falls with the outside temperature (ectothermal).

Heat Loss

Heat is lost from our body through the following four channels:

1. Skin: About 85% of body heat is lost through the skin by convection, conduction and radiation and through evaporation of sweat.
2. Lungs: Heat is lost in the warm air which is breathed out. This loss in warm air can easily be experienced by gently blowing on the back of your hand keeping the mouth wide open. Some heat is also lost during the vaporisation of water from the lungs.
3. Urine and Faeces: These substances are eliminated at body temperature.
4. Foods: Heat is also lost when cold foods, water, or cold beverages are taken into the body.

Mechanism of Heat Loss

Fig: Heat Regulation

1. Vasodilation is the process of increasing (-dilation) the size of blood vessels (vaso-). Greater volumes of blood can now flow near the skin’s surface because to the skin’s expanded peripheral vessels. 
2. This enables our bodies to radiate a significant amount of heat. In this example, the term “radiation” refers to the process of transmitting heat over space using electromagnetic waves.
3. Simultaneously, if a fluid, such as moving air or water in a pool, comes into contact with our skin when we are very hot, heat will be lost through convection. 
4. The greater the amount of our body surface exposed to this (usually) circulating air (e.g. as little clothing as possible), the higher the circulating air’s speed (e.g. it’s really windy), and the smaller the distance between the skin surface and the blood vessels, the greater the heat loss from our body via convection.
5. When our skin comes into contact with a cold object (such as a cold drink), we lose heat by conduction, which is the direct transmission of heat from a hotter surface to a colder surface that is touching that hotter surface.

Perspiration

Fig: Perspiration and evaporation via skin

1. Sweating is another way for the body to regulate its temperature (perspiration). Sweating begins when the body temperature increases above 37 degrees Celsius. Sweat production can be raised or decreased depending on the situation.
2. Sweat production increases when we need to cool down, for example. Sweat drops form on our skin surface and then evaporate, carrying with them our body heat. If all other factors remain constant, the greater the skin surface area and the higher the sweat rate, the greater the rate of sweating cooling.
3. When it comes to body heat loss, the processes of radiation and convection are most effective when the ambient temperature is below 20 degrees Celsius, whereas evaporative cooling accounts for the majority of heat loss when the ambient temperature is above 20 degrees Celsius, especially when it’s above 35 degrees Celsius.
4. Increased humidity, on the other hand, restricts our body’s ability to disperse heat through perspiration.

Functions of the Skin

Skin can perform a variety of tasks that are helpful to the body. These are some of them:

1. Environmental Protection
   For obvious reasons, this is the most vital function of the skin! Pathogens such as viruses and bacteria are kept out of human tissues by the skin, which allows them to enter only through gaps in the skin, such as injuries, or orifices such as the nose and mouth.

2. Prevention of Water Loss
   Amphibians with thin skin must stay near water at all times to avoid drying out. Humans and the majority of other terrestrial animals, on the other hand, have thick skin that allows them to lose very little water. When people live in a desert environment, their skin thickens to prevent water loss due to the dry air!

3. Allowing for Sensation
   The nerves in the skin transmit information to the brain regarding pressure, texture, heat, cold, pain, and pleasure. This enables us to react correctly to our surroundings.

4. Temperature regulation
   a. Sweating allows humans and other mammals to intentionally remove water from their skin. 
   b. Evaporation allows the body to cool itself by leaking water onto the skin. Because the warmest water molecules evaporate first, the final result is that heat is carried out from the body.
   c. The body can also promote heat loss by flushing, which allows heated blood from deep within the body to flow near to the skin and radiate out into the surroundings.
   d. The human phenomenon of “goosebumps” is assumed to represent a vestigial temperature regulating reaction, which many people are unaware of. 
   e. The microscopic arrector pili muscles in our skin tighten when we get goosebumps, causing our vestigial hairs to stand on end. If we had thick fur like our forefathers, extra warm air would be trapped close to our skin, keeping us warm.

5. Camouflage
   Many animals have skin with colours and patterns that help them blend in with their surroundings and avoid being noticed. This is critical for predator and prey species alike. Prey species can’t be eaten if their predator can’t see them, and predators can’t avoid their prey if they can’t see them.

6. Storage
   In the tissues of their skin, many animals store fat and water. This permits these materials to serve as additional insulation while they are awaiting usage.
   Many animals that dwell in cold climes have developed thick layers of “blubber” — fat that acts as a barrier between the outer cold and the animal’s interior organs.

7. Excreting scent signals
   Our skin, as well as the sweat we produce, might have another purpose: it can function as a signal to other animals. Many animals use “scent markers” produced by glands in their skin to identify their territory. Even information about the animal’s age, gender, health, and mate availability can be found in those characteristics.

Thermoregulation

Thermoregulation is the method through which your body keeps its internal temperature constant. The goal of all thermoregulation systems is to bring your body back to a state of homeostasis. This is an equilibrium state. 

In humans, body temperature is controlled by the thermoregulatory centre in the hypothalamus. It receives input from 2 sets of thermoreceptors:

1. Receptors in the hypothalamus monitor the temperature of the blood as it passes through the brain (the core temperature), which remains very close to the setpoint, which is 37 °C in humans. This temperature fluctuates a little but is kept within very narrow limits by the hypothalamus.
2. Receptors in the skin (especially on the trunk) monitor the external temperature.

Fig: Thermoregulatory Centre in Hypothalamus

Response to low temperature

1. Vasoconstriction occurs when the blood arteries beneath the skin receive signals and narrow, reducing blood flow and retaining heat to keep the inside body warm.
2. Thermogenesis is a natural process that occurs in all warm-blooded species. To keep the body warm, the organs produce heat in a variety of ways.
3. Hormonal thermogenesis: The thyroid gland regulates hormone release in this way to enhance the body’s metabolism, which generates more heat to maintain a constant internal body temperature.
4. Reduced sweat production means less heat is lost through evaporation from the skin’s surface.
5. Adrenaline secretion is increased when the adrenal gland produces more of this hormone, which raises the rate of heat production in the liver.

Response to high temperature

1. Sweating: Perspiration glands are stimulated to release sweat, which cools our skin as it evaporates. The interior temperature is lowered as a result of this.
2. Vasodilation is a process in which the blood vessels beneath the skin dilate and increase blood flow, which cools the body by expelling heat through heat radiation.
3. Lowering body hairs – The muscles that adhere to the hairs relax, causing the fur to lie flat and reduce the depth of the layer of insulation.

Heat Stroke or Sunstroke is a condition in which sweat production is unable to keep pace with its evaporation in very hot winds. This results in a rise in body temperature (fever), which may sometimes be fatal. Drinking a lot of water and taking a little more salt in summer is a good precaution against heatstroke.

Behavioural Responses 

Animals respond to heat by resting or lying down with their limbs spread out to increase the amount of body surface exposed to the air. We respond by dressing loosely, turning on fans or air conditioning, and drinking cold beverages.

1. The hypothalamus releases a hormone that prompts the anterior pituitary gland to release thyroid-stimulating hormone as the ambient temperature drops gradually (TSH).
2. TSH causes the thyroid gland to secrete thyroxine into the bloodstream.
3. Thyroxine boosts metabolic rate, which means more heat is produced, especially in the liver.
4. When the temperature rises again, the hypothalamus responds by limiting the anterior pituitary gland’s secretion of TSH, resulting in less thyroxine being produced from the thyroid gland.

Importance of Thermoregulation

The importance of thermoregulation are as follows:

1. The body’s thermoregulation mechanisms are all meant to bring it back to homeostasis or equilibrium.
2. This mechanism helps in the regulation of heat loss and gain, as well as the maintenance of an organism’s optimal temperature range.
3. As previously stated, a healthy body temperature ranges from 37°C to 37.8°C. Hypothermia is a medical emergency that occurs when a person’s body temperature drops from 37°C to 35°C or lower.
4. Cardiac arrest, brain damage, and even death can result from this illness. Hypothermia, or a drop in internal body temperature, is caused by metabolic problems such as a malfunctioning thyroid gland, as well as the use of alcohol and other drugs.

Summary

The body is completely protected by the integumentary system, which includes the skin and its supporting components. The skin is made up of many layers of cells and tissues that are connected to the underlying structures through connective tissue. Heat is lost in four ways: evaporation, convection, conduction, and radiation. If the skin temperature is higher than the ambient air temperature, the body can lose heat by convection and conduction. If the temperature of the ambient air is higher than that of the skin, the body will gain heat by convection and conduction.

In these conditions, the only option for the body to get rid of heat is through evaporation. Everything that prevents normal evaporation elevates the internal body temperature when the ambient temperature is higher than the skin temperature. During intense physical exercise, evaporation becomes the predominant method of heat loss (such as sports). Humidity influences thermoregulation by lowering sweat evaporation and, as a result, heat loss.

FAQs on Skin and Heat Regulation

Q.1. What is the function of the skin?
Ans: With a total area of around 20 square feet, the skin is the body’s largest organ. The skin protects us from microorganisms and the elements, assists in body temperature regulation, and allows us to feel touch, heat, and cold.

Q.2. What is Arrector Pili?
Ans: The Arrector Pili Muscle is a small muscle that connects the base of a hair follicle to dermal tissue on one end and the base of a hair follicle to dermal tissue on the other. The arrector pili muscles contract all at once to generate heat when the body is chilled, causing the hair to “stand up straight” on the skin. 

Q.3. How is heat regulated in the skin?
Ans: The vast blood supply of the skin helps in temperature regulation: dilated vessels enable heat to escape, while constricted vessels retain heat.

Q.4. What is the mechanism for temperature regulation?
Ans: Convection, radiation, conduction, and evaporation are the four mechanisms that the body utilises to regulate temperature.

Q.5. What part of the skin is responsible for temperature regulation?
Ans: Insensible perspiration is a process in which the dermis regulates body temperature by producing sweat and controlling evaporation. Sweat is produced by sweat glands in the dermis, which then evaporates on the skin’s surface.

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