THERMOREGULATORY MECHANISM

BY: TAHIR RAMZAN BHAT

CLASS SEMINAR ON

What is Thermoregulation

The ability of an organism to keep its body temperature with in a certain range when temperature surrounding is extremely different.

Homeostasis

The human body has the ability to maintain a constant internal environment so that every organ and cell is provided the perfect conditions to perform its functions. This is called homeostasis. However, every organ plays a role in maintaining a constant internal environment. For example the lungs are responsible for the supply of oxygen to cells. The liver is to maintain a constant level of glucose and amino acids, and so on..

Temperature Regulation

A healthy human should have a body temperature of 37°C.  If the body temperature drops below 37°C, metabolic reactions become slower because molecules move slower and have less kinetic energy. If the temperature rises above 37°C, the enzymes of the body begin to get denatured and metabolic reactions will be much slower.

Sometimes, the temperature of the area you are at is low enough to decrease your body temperature. Sometimes it is high enough to raise your body temperature. That is why the body has the ability to control its body temperature. Our skin is responsible for this process.

Monitoring body temperatureIn humans and other mammals, the core body

temperature is monitored by a part of the brain called thermoregulatory centre. This is located in the hypothalamus of the brain.

It acts as the body’s thermostat ( a switch that is turned on and off by a change in temperature, eg in iron box).

Various methods and sites can be used for temperature recording e.g. conventional clinical mercury thermometer, skin electronic forehead thermometer, thermistor probes etc.

The skin and temperature control.Functions of the skin

• Forming a tough outer layer able to resist mechanical damage.

• Acts as barrier to the entry of disease- causing micro organisms.

• Forming an impermeable surface, preventing loss of water.

• Acts as a sense organ for touch and temperature changes.

• Controls heat loss through the body surface.

The Structure and Function of the Skin.

The skin is an organ that coats your entire body. The skin is made up of three layers, the Epidermis, the dermis and hypodermis.

The epidermis’s main function is to protect the dermis which contains most of the structures, and protect the body from ultra-violet rays. The surface of the epidermis is made of tough, dead cells.

The Human Skin

Thermoregulation in Heat

Body Temperature Cotrol

It is controlled by balance between heat production and heat loss.

Heat production = Heat lossTotal body temperature as a result can be expressed as:

Body Temperature = heat produces metabolically

+ heat gained from the environment

- heat lost to the environment

How is temperature controlled?Body temperature is monitored and controlled by temperature receptors in the skin and brain (thermoregulatory centre)Thermoregulatory centre is situated in the hypothalamus – in the brain.

Thermoregulatory centreThese receptors detect changes in the temperature of blood flowing through those areas.

If body temperature deviates from 37 °C, these receptors send out electrical signals to the thermoregulatory centre that trigger actions that increase or decrease heat loss.

Hypothalamus Regulation of Temperature

• Hypothalamus acts as “thermostat” that makes thermoregulatory adjustments to deviations from temperature norm in the brain (37 C ± 1 C or 98.6±1.8 F ).

HYPOTHALAMUS

1. ANTERIOR HYPOTHALAMUS:this center controls heat dissipating events. If this center is stimulated, the blood vessels of the skin are dilated, thus resulting in a greater flow of blood to the surface. Also impulse are transmitted to the sweat gland increasing perspiration. All these physiological responses act to increase the rate of heat loss from the body and thereby prevent overheating of the body

2. POSTERIOR HYPOTHALAMUS:This center calls on heat conservation events and thereby prevents chilling of the body. If this center is stimulated, the blood vessels of the skin are constricted, thus reducing the blood flow to the surface. In addition to this, surface hairs on the body are also stimulated to become erect, thus insulating layer of air surrounding the skin. At the same time, shivering is brought about through the same mechanism, to increase heat production.

the adrenal medulla and thyroid gland also take part in the regulation of either heat production or heat loss. When the adrenal medulla is stimulated, large amount of epinephrine and norepinephrine hormone are released into the blood. These two hormones have ability to increase the basal metabolic rate and therefore increase heat production.

when the thyroid gland is stimulated, large quantities of the hormone called thyroxine is released into the blood. Its action is similar to that of norepinephrine, however the thyroxine continues to be active for as long as 4 to 8 weeks, after its release into the blood. Norepinephrine on the other hand, remains active for only few minutes. Large secretion of the thyroid hormone can cause the metabolic rate to increase as much as 200% of normal.

Endocrine Glands Involved in Temperature regulation

Heat Production

It is the by-product of metabolism.Factors determining rate of heat production:1.Basal rate of metabolism2.Extra rate of metabolism caused by muscle activity3.Extra rate of metabolism caused by effect of thyroxine.4.Extra rate of metabolism caused by epinephrine/nor-

epinephrine/sympathetic stimulation5.Extra rate of metabolism caused by chemical activity in

cells.6.Extra rate of metabolism needed for digestion, absorption

and storage of food.

HEAT LOSSHeat produced in deeper tissues of body is transferred to skinand is lost to air.Factors determining the rate of heat loss:1.How rapidly heat is conducted from where it is produced in

body core to skin.2.How rapidly heat is transferred from skin to surroundings.●increased blood flow to skin increases the rate of heat transfer.

Thermoregulation

PHYSICAL PROCESSES TO EXCHANGE HEAT WITH THE ENVIRONMENT

These four processes as a very important factor to exchange their body heat or temperature with the outside stimuli

CONDUCTION

     The direct transfer of thermal motion between molecules of the environment and those on the surface body of an human.

     This transfer is from an area of higher temperature to one of lower temperature because heat moves down thermal gradients.

 

Ex. When a person sit on a cold ground, he lose heat, and when he sit on warm sand, he gains heat

CONVECTION

   Movement of air or a liquid over the surface of a body

   It contributes to heat loss if the air is cooler than the body or heat gain if the air is warmer than the body

 

Ex. On a cool day, the body of a person loses heat by convection because the skin temperature is higher than the surrounding air temperature.

EVAPORATION

   Heat is lost from the body via sweat. Even when a person is not sweating, water still evaporates.

Loss of heat from a surface as water molecules escape in the form of a gas   

Ex. Humans, and some other mammals have sweat glands that actively move watery solutions through pores to the skin surface. When skin temperature is high, water at the surface absorbs enough thermal energy to break the hydrogen bonds holding the individual water molecules together, and they depart from the surface, carrying heat with them. As long as the environmental humidity is low enough to permit complete evaporation, sweating can rid the mammalian body of excess heat, however, the water must evaporate. Sweat dripping from a mammal has no cooling effect at all.

RADIATION

  Loss of heat by radiation means loss in the form of infrared heat rays. If the temperature of the body is greater than the temperature of the surroundings, a greater quantity of heat is radiated from the body than is radiated to the body.

The emission of electromagnetic waves that objects, such as another animal’s body or the sun, produce

    Radiation can transfer heat between objects that are not in direct contact with each other, as happens when an animals suns itself.

EXERCISE IN THE HEAT

Exercising in hot weather puts extra stress on your body. If you don't take care when exercising in the heat, you risk serious illness. Both the exercise itself and the air temperature increase your core body temperature.To help cool itself, your body sends more blood to circulate through your skin. This leaves less blood for your muscles, which in turn increases your heart rate. If the humidity also is high, your body faces added stress because sweat doesn't readily evaporate from your skin. That pushes your body temperature even higher.

PHYSIOLOGICAL CHANGES IN HUMID ENVIRONMENT

High heat and humidity reduce body’s ability to loose heat by radiation, convection and evaporation respectively. This inability to loose heat during exercise in a hot/humid environment results in a great core temperature and a higher sweat rate. This combined effect of fluid loss and high core temperature generally has determined effects on performance in endurance events and increases the risk of hypothermia and heat injury

THERMOREGULATION IN SPORT

• The harder the muscles are working, the more heat is generated.

• The more energy that is being processed by the body the more heat is being generated.

• If the environment is warmer than the body, no heat can be removed from the body.

Cont...

• At the same time, if the environment is too cold, then heat will be lost too quickly.

• Due to increased or decreased temperature effects the flow of blood, the contractions of all the muscles (including the heart) and the functions of the nervous system.

• Clothing will play a large role in this, as we’ll see in our experiment next session!

KEY TERMS

• Hyperthermia – a condition in which body temperature is elevated to a very high level

• Hypothermia – a condition in which body temperature is lowered to a very low level

• Hypohydration – a condition in which there are very low levels of fluid in the body