The human body maintains a constant internal temperature of around 37°C through thermoregulation. The hypothalamus acts as the thermostat, monitoring internal temperature and triggering physiological responses like sweating or shivering to increase or decrease heat loss from the skin. When body heat production exceeds heat loss to the environment through conduction, convection, evaporation and radiation, core temperature rises, while imbalance in the other direction causes core temperature to fall. Strenuous exercise can challenge this system by greatly increasing heat production, requiring enhanced cooling to prevent overheating.

1. BY: TAHIR RAMZAN

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

3. 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..

4. 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.

5. Monitoring body temperature
In 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.

6. 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.

7. 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.

8. The Human Skin

9. Thermoregulation in Heat

10. Body Temperature Cotrol
It is controlled by balance between heat production and heat
loss.
Heat production = Heat loss
Total body temperature as a result can be expressed as:
Body Temperature = heat produces metabolically
+ heat gained from the environment
- heat lost to the environment

12. 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 centre
These 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.

13. 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 ).

14. 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

15. 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.

17. 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

18. Heat Production
It is the by-product of metabolism.
Factors determining rate of heat production:
1.Basal rate of metabolism
2.Extra rate of metabolism caused by muscle activity
3.Extra rate of metabolism caused by effect of thyroxine.
4.Extra rate of metabolism caused by epinephrine/nor-
epinephrine/sympathetic stimulation
5.Extra rate of metabolism caused by chemical activity in
cells.
6.Extra rate of metabolism needed for digestion,
absorption and storage of food.

19. HEAT LOSS
Heat produced in deeper tissues of body is transferred to skin
and 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.

20. Thermoregulation

21. 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

22. 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.

23. 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.

24. 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.

26. 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.

27. 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

28. 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.

29. 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!

30. 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