The ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different is called THERMOREGULATION. It is important to maintain a fairly steady body temperature as each species has a preferred body temperature at which functioning is normal. The contents of this presentation are: homeostasis, metabolic rate, endotherms, ectotherms, heat balance, concept of heat transfer, counter current heat exchange, torpor, hibernation and aestivation.

1. SUBMITTED TO:
DR. RAKHI SHARMA
HOD ZOOLOGY
STANI MEMORIAL PG COLLEGE, JAIPUR
• 2017-18
UNIVERSITY OF RAJASTHAN
THERMOREGULATION
SUBMITTED BY:
SUNIDHI
M.SC. ZOOLOGY (PRE.)

2. INTRODUCTION:
The ability of an organism to keep its body temperature within certain boundaries,
even when the surrounding temperature is very different is called
thermoregulation. It is important to maintain a fairly steady body temperature as
each species has a preferred body temperature at which functioning is normal.
The ability of an organism to simply adopt the surrounding temperature as its own
body temperature, thus avoiding the need for internal thermoregulation is called
thermoconformation.

3. CONTENTS:
• Homeostasis
• Metabolic rate
• Endotherms
• Ectotherms
• Heat balance
• Concept of heat transfer
• Counter current heat exchange
• Torpor
• Hibernation
• Aestvation
• Reference

4. HOMEOSTASIS:
A state of dynamic stability in an organism’s internal conditions, maintained from
thermal equilibrium with its environment is called homeostasis.
Hyperthermia: If the body is unable to maintain a normal temperature and it increases
significantly above normal. For humans, this occurs when the body is exposed to
constant temperature of approx. 55°C (131 F) and prolonged exposure at this
temperature and upto around 75˚C death is almost unavoidable.
Hypothermia: When body temperature decrease below normal level. It results when
the homeostatic control mechanism of heat within the body malfunction, causing the
body to lose heat faster than producing it. Hypothermia sets in when the core body
temperature get lower than 35°C.

5. METABOLIC RATE:
The metabolic rate is the amount of energy consumed minus the amount of
energy expanded by the body. The basal metabolic rate (BMR) describes the
amount of daily energy expanded by humans at rest, in a neutrally temperature
environment, while in the postabsorptive state. It measures how much energy the
body needs for normal, basic, daily activity.
About 70% of the daily energy expenditure comes from the basic functions of the
organs in the body. Another 20% comes from physical activity, and remaining 10%
is necessary for body thermoregulation.
This rate will be higher if a person is more active or has more lean body mass. As
you age, the BMR generally decrease as the percentage of less lean muscles mass
decrease.

6. ENDOTHERMS:
Endotherms generate most of the heat they need internally. When it’s cold out,
they increase metabolic heat production to keep their body temperature constant,
so their internal body temperature is independent of temperature of the
environment.
People, polar bears, penguins, and prairie dogs, birds and mammals are
endotherms.

7. ECTOTHERMS:
For ectotherms, body temperature mainly depends on external heat sources. That
is, ectotherms body temperature rises and falls along with the temperature of the
surrounding environment. Examples: amphibians, invertebrates and most fishes.
Although ectotherms do generate metabolic heat like all living things. Ectotherms
can’t increase this heat production to maintain a specific internal temperature.

8. HEAT BALANCE:
For both endotherms and ectotherms body temperature depends on the balance
between heat generated by the organism and heat exchanged with – lost to or gained
from – the environment.
There are three main ways that an organism can exchange heat with its environment:
radiation, conduction along with convection and evaporation.
• Radiation is the transfer of heat from a warmer object to a cooler one by infrared
radiation, that is without direct contact.
• Conduction: Heat can be transferred between two objects in direct contact by
means of conduction. Conduction of heat between your skin and nearby air or water
is aided by convection, in which heat is transferred through movement of air or
liquid.

9. • Evaporation: Vaporization of water from a surface leads to loss of heat for
example, when sweat evaporates from your skin.

10. MECHANISM OF HEAT BALANCE:

11. NEED OF TEMPERATURE REGULATION:
There are some basic limits on survivable body temperature for most animals. The
rate of chemical reactions changes with temperature, both because temperature
affects the rate of collisions between molecules and because the enzymes that
control the reactions may be temperature sensitive.
Reactions tend to go faster with high temperature, up to a point, beyond which
their rate drops sharply as their enzymes denature.
Each species has its own network of metabolic reactions and set of enzymes
optimized for a particular temperature range. By keeping body temperature in that
target range, organisms ensure that their metabolic reactions run properly.

12. CONCEPT OF HEAT TRANSFER:
The body is divided into a warm internal core and a cooler outer shell.
Internal core: The internal body temperature is the temperature of the vital organs
inside the heat and trunk, which, together with a variable amount of other tissue,
comprise the warm internal core. The hypothalamus in brain is master switch that
regulate body’s core temperature.
The temperature of internal core of the body remains very constant, within +/- 1 F.
Outer shell: The temperature of outer shell is strongly influenced by the
environment. The thermoregulatory responses strongly affect the temperature of
the shell, specially the skin.

14. COUNTERCURRENT HEAT EXCHANGE:
Countercurrent heat exchange is a common mechanism in organisms that utilizes
parallel pipes of flowing fluid in opposite directions in order to save energy.
Concurrent flow is not as efficient as countercurrent flow in retaining energy.

15. COUNTERCURRENT HEAT EXCHANGE IN WHALE’S TONGUE:
A whale’s tongue uses this system. As blood flows to the tip of the tongue, it heats
up blood returning to the body.

16. Gray whales take in many galloons of cold sea water into their mouth at a time, and
this results to be a large heat sink.
If the gray whales were to lose a significant amount of heat to the water, it wouldn’t
be able to eat enough food to produce the energy required to heat its body. It was
therefore essential for its survival to have a system to conserve energy in the form
of heat. Through natural selection, a countercurrent heat exchange system was
established in the gray whale’s tongue through an artery, it gives off heat to the
blood returning to the whale through its veins.
This is a significant way to save heat, as the heat would otherwise be lost to the
water that the whale swallows.

17. TORPOR:
Torpor is the state of decreased physiological activity in an animal, usually by a
reduced body temperature and metabolic rate. It enables animals to survive
periods of reduced food availability.
• It can refer to a period of low body temperature and metabolism lasting less
than 24 hours, as in ‘daily torpor’. Examples: Humming bird, mice and bats.
• During the active part of the day, such animals maintain normal body
temperature and activity levels, but their metabolic rate and body temperature
drops during a portion of the day( usually night) to conserve energy.

18. • Torpor is often used to help animals survive during periods of colder
temperature, as it allows them to save the energy that would normally be used to
maintain a high body temperature.
• Slowing metabolic rate to conserve energy in times of insufficient resources is the
primarily noted purpose of torpor.
• Daily torpor is seasonally dependent and can be an important part of energy
conservation at any time of year.
• Hibernation and aestivation are made up of multiple bouts of torpor.

19. HIBERNATION:
Hibernation is the state of inactivity and metabolic depression in endotherms during
winter. It is characterized by low body temperature, slow breathing and heart rate, and
low metabolic rate.
• The function of hibernation is to conserve energy when sufficient food is
unavailable. To achieve this energy saving, an endotherm decreases its metabolic
rate, which then decreases body temperature.
• Before entering hibernation, animal need to store enough energy to last through
entire winter. Large species eat large amount of food and store the energy in fat
deposits. In small species food catching replaces eating and becoming fat.
• Some species of mammals hibernate while gestating young, which are born either
while the mother hibernates or shortly afterwards. Example: female polar bear.

20. Obligate hibernation:
The animals that spontaneously, and annually, enter hibernation regardless of
ambient temperature and access to food. Example: ground squirrels, rodents.
Faculative hibernation:
Faculative hibernators only enter hibernation when either cold stressed, heat
deprived, or both.
The white- tailed praire dog is an obligate hibernator and the closely related
tailed praire dog is a faculative hibernator.

21. AESTIVATION:
Aestivation is a state of animal dormancy, similar to hibernation, characterized by
inactivity and a lowered metabolic rate, that is entered in response to high
temperatures and arid conditions.
• It takes place during times of heat and dryness, which are summer months.
• This is done to avoid damage from high temperatures and risk of desiccation.
• The primary physiological and biochemical concerns for an aestivating animal
are to conserve energy, retain water in the body, ration the use of stored energy,
handle the nitrogenous end products, and stabilize body organs, cells,
macromolecules and tissues.

22. • The depression of metabolic rate during aestivation causes a reduction in
macromolecule synthesis and degradation.
• To stabilize the macromolecules, aestivators will enhance antioxidant defense and
elevate chaperone proteins.
• In other words, animals who aestivate go through nearly the same physiological
processes as animals that hibernate.

23. REFERENCES:
• https://en.m.wikipedia.org/wiki/Thermoregulation
• www.khanacademy.org/scienc/biology/principles-of-physiology/metabolism-
and-thermoregulation/a/endotherms-ectotherms
• http://minerva.union.edu/linthicu/concurrent.htm
• http://scienceblogs.com/grrlscientist/2006/04/09/hummingbirds-and-torpor
• https://en.m.wikipedia.org/wiki/Aestivation
• https://en.m.wikipedia.org/wiki/Hibernation

24. Thank you