The document discusses thermoregulation in vertebrates, detailing how animals maintain body temperature despite environmental fluctuations through physiological and behavioral mechanisms. It distinguishes between ectotherms and endotherms, outlining their temperature regulation strategies and adaptations to cold and warm environments. The role of the hypothalamus in temperature control in humans is also highlighted, indicating the complexity of thermoregulatory processes across different species.

1. THERMOREGULATION IN
VERTEBRATES
SUBMITTED BY:
NAMARTA SHARMA
06-ZOOL-18
M.SC. SEM 2ND

2. Thermoregulation is a complex and important physiological process that
maintains, to varying degrees, an animal’s body temperature, despite variations in
environmental temperature.
Animals have successfully colonized the varied places on earth by possessing
homeostatic mechanisms for maintaining a relatively constant internal environment,
despite fluctuations in the external environment.
Homeostasis is the state of steady internal conditions maintained by living things.
The ability to control the body temperature is called thermoregulation and involves
the nervous, endocrine, respiratory and circulatory systems in higher animals.
Thermoconforming organisms adopt surrounding temperature as their own body
temperature and there is no need of internal thermoregulation.

3. IMPACT OF TEMPERATURE ON ANIMAL LIFE
The rate of cellular respiration increases with temperature up to a certain point.
The enzymes most efficiently catalyze their chemical reactions at an optimum
temperature.
The chemical interactions holding the enzymes together in their three-
dimensional shape are disrupted when there is rise in temperature.
High temperatures cause the proteins in nucleic acids to denature and low
temperatures may cause membranes to change from a fluid to a solid state,
which can interfere with many cellular processes, such as active-transport pumps.
Animals can guard against these damaging effects of temperature fluctuations by
balancing heat gains and heat losses with their environment.

4. HEAT GAINS AND LOSSES
Animals produce heat as a by-product of metabolism, and either gain heat from, or lose it to, the
environment.
Body temperature = heat produced metabolically + heat gained from the environment – heat
lost to the environment
Animals use four physical processes to exchange heat with the environment : conduction, convection,
evaporation, and radiation.
Conduction is the direct transfer of thermal motion (heat) between molecules of the environment and
those on the body surface of an animal.
Convection is the movement of air or a liquid over the surface of a body and contributes to heat loss
(if the air is cooler than the body) or heat gain (if the air is warmer than the body).
Evaporation is loss of heat from a surface as water molecules escape in the form of a gas.
Radiation is the emission of electromagnetic waves produced by objects, such as another animal’s
body or the sun.

6. SOLUTIONS TO TEMPERATURE FLUCTUATIONS
Three basic ways:
1. They can occupy a place in the environment where the temperature remains
constant and compatible with their physiological processes,
2. Their physiological processes may have adapted to the range of
temperatures in which the animals are capable of living,
3. They can generate and trap heat internally to maintain a constant body
temperature, despite fluctuations in the temperature of the external
environment.

7. SOME IMPORTANT TERMS
Hyperthermia: Condition that occurs when body is unable to maintain a normal
temperature and increases significantly above normal.
Hypothermia: Occurs when body temperature decreases below normal level. It
results when homeostatic control of mechanisms of heat within the body
malfunction, causing the body to lose heat faster than producing it.
Thermal acclimation: Capacity to tolerate temperature changes below and above
normal tolerable range by shifting homeostatic mechanisms in accordance with
the changed thermal states of the environment.

8. Animals can be categorized as ectotherms or endotherms, based on whether their source of body heat
is from internal processes or derived from the environment.
Ectotherms (cold-blooded) derive most of their body heat from the environment rather than from their
own metabolism. They have low rates of metabolism and are poorly insulated. In general, reptiles,
amphibians, fishes and invertebrates are ectotherms, although a few reptiles, insects and fishes can
generate some internal heat.
Endotherms (warm-blooded) obtain their body heat from cellular processes. Birds and mammals are
endotherms.
Another way of categorizing animals is based on whether they maintain a constant or variable body
temperature.
Most endotherms are homeotherms(have a relatively constant body temperature)and most
ectotherms are heterotherms(have a variable body temperature) or poikilotherms.
But there are many exceptions. Some endotherms vary their body temperatures
seasonally(hibernation),others vary it on a daily basis.

9. BRAIN CONTROL
In both ectotherms and endotherms, temperature regulation is controlled by preoptic area of anterior
hypothalamus.
It is separate from sensation of temperature (thermoreceptors).

11. TEMPERATURE REGULATION IN FISHES
Body temperature of most fishes is determined by their surrounding water temperature. Fishes that
live in extremely cold water have antifreeze materials in their blood. Polyalcohols or water soluble
peptides and glycopeptides lower the freezing point blood plasma and other body fluids. These fishes
also have proteins or protein-sugar compounds that stunt the growth of ice crystals that begin to form.
These adaptations enable these fishes to stay flexible and swim freely in a supercooled state.
Some very active fishes maintain a core temperature significantly above the temperature of the water.
Bluefin tuna and the great white shark have their major blood vessels just under the skin. Branches
deliver blood to the deeper, powerful, red swimming muscles where smaller vessels are arranged in a
countercurrent heat exchanger called the rete mirabile. The heat generated by these red muscles
is not lost because it is transferred in the rete mirabile from venous blood passing outward to cold
arterial blood passing inward from the body surface. This arrangement of blood vessels enhances
vigorous activity by keeping the swimming muscles several degrees warmer than the tissue near the
surface of the fish.

14. TEMPERATURE REGULATION IN AMPHIBIANS AND REPTILES
Most of these animals are ectotherms, they derive heat from their environment and their body
temperatures vary with external temperatures.
Most amphibians have difficulty in controlling body heat because they produce little of it metabolically
and rapidly lose most of it from their body surfaces. Behavioural adaptations enable them to
maintain their body temperature within a homeostatic range most of the time. Amphibians have an
additional thermoregulatory problem because they must exchange oxygen and carbon oxide across
their skin surface, and this moisture layer acts as a natural evaporative cooling system. This
problem of heat loss through evaporation limits the habitats and activities of amphibians to warm,
moist areas. Some amphibians such as bullfrogs can vary the amount of mucus they secrete from
their body surface-a physiological response that helps regulate evaporative cooling.
Reptiles have dry rather than moist skin, which reduces loss of body heat through the skin through
evaporative cooling. They also have an expandable ribcage which allows for more powerful and
efficient ventilation. Reptiles are almost completely ectothermic. They have low metabolic rate and
warm themselves by behavioural adaptations.

17. TEMPERATURE REGULATION IN BIRDS AND MAMMALS
Birds and mammals can live in habitats all over the earth because they are homeothermic
endotherms.
Various cooling mechanisms prevent excessive warming in birds. Because they have no sweat
glands, birds pant to lose heat through evaporative cooling. Some species have a highly
vascularized pouch(gular pouch) in their throat that they can flutter(gular flutter) to increase
evaporation from the respiratory system. Feathers are excellent insulators for the body, especially
down type feathers that trap a layer of air next to the body to reduce heat loss from the skin.
Aquatic species face the problem of heat loss from their legs and feet. They have peripheral
counter current heat exchange vessels called a rete mirabile in their legs to reduce heat loss.
Marine animals such as seals and whales have thick pelts and a thick layer of insulating fat called
blubber just under the skin, in the tail and flippers, where there is no blubber, a counter current
system of arteries and veins helps keep heat loss to a minimum.
Birds and mammals also use behavioural mechanisms to cope with external temperature
changes. They can sun themselves or seek shade as the temperature fluctuates. Many animals
huddle together to keep warm, other shares burrows for protection from temperature extremes.
Migrations to warm climates and hibernation enable many different birds and mammals to survive
through the harsh winter months.

20. Strategies in cold environment:
1. Piloerection- Small smooth muscles (arrector pili in mammals) attached to feather or hair shafts
distorts surface of skin making feather/hair shaft stand erect (goosebumps /pimples). To slow
movement of air across skin and minimize heat loss.
2. Increase in body size to more easily maintain core body temperature (Bergmann’s rule).
3. Ability to store energy as fat for metabolism.
4. Shortened extremities.
5. Countercurrent blood flow in extremities.
6. Shivering.
7. Vasoconstriction.
8. Non-shivering thermogenesis.
Strategies in warm conditions:
1. Behavioral adaptations- living in burrows during day and being nocturnal.
2. Evaporative cooling by perspiration and panting.
3. Storing fat reserves in one place (camel’s hump) to avoid its insulating effect.
4. Elongated, often vascularized extremities to conduct body heat to the air.
5. Vasodilation.
6. Sweating.

21. Some additional processes:
Sweat glands: Evaporation across respiratory surfaces or across skin through sweat glands.
Animals with body covered with fur have limited ability to sweat, rely on panting to increase
evaporation across moist surfaces of lungs and tongue and mouth. Example: cats, dogs, pigs.
Sweat glands only in foot pads and snout. Sweat produced on paws, sole and palm is to
increase friction and enhance grip.
Thick skin, continuous layer of insulating fat beneath dermis in case of mammals.
Shivering: When the core body temperature drops, the shivering reflex is triggered to maintain
homeostasis.
Animals living in desert, e.g., camels, have dense coats to prevent heat gain.
Torpor: Short term temporary drop in body temperature to survive cold frosty nights. Low
metabolic rate is less energetically expensive. Example, Daily torpor in bats.
Hibernation: State of inactivity and metabolic depression in endotherms, characterized by low
body temperature, slow breathing and heart rate, low metabolic rate etc. Example: Hibernating
bears.
Aestivation: State of animal dormancy, taking place in summer, characterized by inactivity and a
lowered metabolic rate, in response to high temperatures and arid conditions.

23. Thermoregulation in humans
Adaptations to varying climatic conditions includes both physiological mechanisms resulting from
evolution and behavioral mechanisms resulting from conscious cultural adaptations.
The physiological control of the body’s core temperature takes place primarily through
hypothalamus, which assumes the role as body’s thermostat. It possesses control mechanisms as
well as key temperature sensors, which are connected to nerve cells known as thermoreceptors.
Scattered through the body in both PNS and CNS, these nerve cells are sensitive to changes in
temperature and are able to provide useful information to the hypothalamus through the process of
negative feedback, thus maintaining a constant core temperature.

27. REFERENCES
~ Zoology by Miller and Harley
~ ebay.co.uk
~ Wikipedia
~ Shutterstock.com