Warm Blooded

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Warm blooded animals2

In biology, a warm-blooded animal species is one whose members maintain thermal homeostasis; that is, they keep their body temperature at a roughly constant level, regardless of the ambient temperature.

This involves the ability to cool down or produce more body heat. Warm-blooded animals mainly control their body temperature by regulating their metabolic rates (e.g. increasing their metabolic rate as the surrounding temperature begins to decrease).


Warm-bloodedness generally refers to three separate aspects of thermoregulation.


A large proportion of the creatures traditionally called "warm-blooded" (mammals and birds) fit all three of these categories.

Studies in the field of animal thermophysiology have revealed many species belonging to these two groups that don't fit all these criteria. For example, many bats and small birds are poikilothermic (opposite of Homeothermy) and bradymetabolic when they sleep for the night (or day, as the case may be).

Mechanism in warm blooded animals5

The creatures traditionally regarded as warm-blooded have a larger number of mitochondria per cell, which enables them to generate heat by increasing the rate at which they "burn" fats and sugars.

This requires a much greater quantity of food than is needed by cold-blooded animals in order to replace the fat and sugar reserves.

In many endothermic animals a controlled state of hypothermia called hibernation, or torpor conserves energy by lowering the body temperature

Heat loss is a major threat to smaller creatures as they have a larger ratio of surface area to volume. Most small warm-blooded animals have insulation in the form of fur or feathers. Aquatic warm-blooded animals generally have deep layers of fat under the skin for insulation, since fur or feathers would spoil their streamlining

Many warm-blooded animals blanch (become paler) in response to cold, which reduces heat loss by reducing the blood flow to the skin.

Mechanism in warm blooded animals6

Cold blooded scorpion

Avoid over heating7

In equatorial climates and during temperate summers over-heating is as great a threat as cold. In hot conditions many warm-blooded animals increase heat loss by panting and or flushing (increasing the blood flow to the skin).

Hairless and short-haired mammals also sweat, since the evaporation of sweat consumes a lot of heat.

Elephants keep cool by using their huge ears like radiators in automobiles: they flap their ears to increase the airflow over them.

Warm blooded lizard

Cold blooded lizardAdvantages of warm bloodedness8

Warm-blooded animals have much greater stamina than cold-blooded creatures of the same size and build, because their faster metabolisms quickly regenerate energy supplies (especially ATP) and break down muscular waste products (especially lactate).

Warm-blooded creatures can be active at more time during the diurnal cycle in places of sharp temperature differences between day and night

Warm blooded animal (homeothermic ) ihas the ability to maintain its constant body temperature even in freezing cold weather

Because of warm blooded nature, mammals are less prone to fungal diseases.

Thermographic image: a coldblooded snake is eating a warmblooded mouseDisadvantages of warm bloodedness9

Because warm-blooded animals use enzymes which are specialized for a narrow range of body temperatures, over-cooling rapidly leads to torpor and then death.

Also, the energy required to maintain the homeothermic temperature comes from food - this results in homeothermic animals needing to eat much more food than poikilothermic animals.

Shivering and fat-burning to maintain temperature are very energy-intensive, for example:in winter many small birds lose one third of their body weight overnight.

in general a warm-blooded animal requires 5 to 10 times as much food as a cold-blooded animal of the same size and build, so cold-blooded animals are better at surviving in barren environments

Thermoregulation10

Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different.

If the body is unable to maintain a normal temperature and it increases significantly above normal, a condition known as hyperthermia occurs.

The opposite condition, when body temperature decreases below normal levels, is known as hypothermia.

Thermoregulation in both ectotherms and endotherms is controlled mainly by the preoptic area of the anterior hypothalamus.Such homeostatic control is separate from the sensation of temperature.

Most body heat is generated in the deep organs, especially the liver, brain, and heart, and in contraction of skeletal muscles.

Thermoregulation11

Ectotherms are animals which regulate their body temperature via external means.

These animals are reliant on the environment for the gain or loss of heat.

As such, they need behavioral and structural adaptations for regulation of heat.

Thermoregulation in ectotherms12

Adaptions to warm up13

As ectotherms need to gain heat from the environment, they display certain behaviour which allows them to warm up.

Basking in the Sun is the most commonly seen method, especially with the terrestrial reptiles, amphibians and arthropods, as the Sun is the main source of the Earths heat.

The marine iguana inhabits only the Galapagos Islands, and it is the only lizard to have evolved to forage at sea.They occupy the barren rocks by the shore which are devoid of food, as such, they mainly feed on seaweed, found in the sea around them.

Challenge:: The sea around the Galapagos Islands remains cold all year round. Marine iguanas must thus gain enough body heat for them to survive the chilling temperatures of the sea (15-16oC).

Marine inguana14

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The Solution: The marine iguana exploits the rocks they live on to increase their body temperature rapidly.---They gather at the uppermost rocks (which are the warmest) near the shore and bask in the sun for approximately half-an-hour before entering the seas to forage for seaweed

The Physics behind the solution:

The iguanas conduct heat through conduction and radiation.

Conduction: The iguanas conduct heat from the hot rocks. As heat is conducted more quickly through solids via lattice vibration, they are able to conduct heat rapidly.

Radiation: Heat energy from the Sun is transferred by EM waves to the iguana. Marine iguanas are also black, increasing heat absorbed via radiation as black surfaces are good absorbers of radiant energy.

Marine inguana15

Marine inguana16

Image Credits: http://www.photostuff.org/galapagos.html

RadiationConductionImage Credits: http://www.photostuff.org/galapagos.htmlCrocodiles often lies near the river bank with its mouth wide open in the heat of the afternoon, remaining almost motionless.

The Physics behind their behaviour:

The greater the exposed surface area, the more heat lost through radiation. As such, by opening its mouth and increasing its exposed surface area, the crocodile increases the rate of heat loss.

Increase the rate of water vapour escaping from its body.

As water absorbs thermal energy from the crocodile when it changes into water vapour, the body temperature of the crocodile is reduced.Crocodile17

The Namaqua Chameleon lives in the extreme conditions of the desert.Living solitarily, they spend much time searching for mates.

The Challenge: To heat up as quickly as possible in the morning, the only time of the day it is cool enough for them to be active.

The Solution: The Namaqua Chameleon uses its colour changing abilities.

The side of the body facing the sun becomes darker-coloured.

The side of the body facing away from the sun becomes lighter-coloured.

Namaqua Chameleon18

The Physics behind the solution:

Darker-coloured surfaces are good absorbers of radiant energy from the sun.

As such, making the side facing the sun darker-coloured increases the heat energy absorbed from the sun, allowing it to warm up quickly

Lighter-coloured surfaces are poor emitters of radiant energy.

As such, making the other side white decreases the heat energy lost from the chameleon by reducing the heat emitted.

Namaqua Chameleon19

Just like the Namaqua Chameleon, the Sidewinder also lives in the extremely hot desert.They are also active during parts of the day when temperatures are relatively low.

The Challenge: To prevent themselves from overheating in the desert.

The Solution: The sidewinder moves in a manner which obtained it its name- sidewinding, moving via side-to-side motions across the sandSidewinder20

`The Physics behind The Solution:Recall the formula for the rate of conduction:

A in the formula represents the cross-sectional surface area between two objects.

Through sidewinding, at any one point in time, only two small sections of the snakes body comes into contact with the desert sand, reducing the cross-sectional surface area A.As such, Q/t is reduced greatly, preventing the sidewinder from conducting too much heat.Sidewinder21

An endotherm is an organism that produces heat through internal means, such as muscle shivering or increasing its metabolism.

Many endotherms have a larger number of mitochondria per cell than ectotherms, which enables them to generate heat by increasing the rate at which they metabolize fats and sugars.

In many endothermic animals, a controlled state of hypothermia, called hibernation or torpor, conserves energy by lowering the body temperature.Endotherms22

In cold environments, birds and mammals employ the following adaptations and strategies to minimize heat loss:

1.using small smooth muscles (erector pili in mammals) which are attached to feather or hair shafts; this non-shivering thermogenesis distorts the surface of the skin as the feather/hair shaft is made more erect (called goose bumps or pimples)

2.increasing body size to more easily maintain core body temperature (warm-blooded animals in cold climates tend to be larger than similar species in warmer climates.)Thermoregulation in Birds and animals23

3.having the ability to store energy as fat for metabolism.

4.have shortened extremities.

5.have countercurrent blood flow in extremities - this is where the warm arterial blood travelling to the limb passes the cooler venous blood from the limb and heat is exchanged warming the venous blood and cooling the arterial

Thermoregulation in Birds and animals24

Kangaroo licking its arms to cool down on a very hot day

In warm environments, birds and mammals employ the following adaptations and strategies to maximize heat loss:

1.behavioural adaptations like living in burrows during the day and being nocturnal.

2.evaporative cooling by perspiration and panting.

3.storing fat reserves in one place (e.g. camel's hump) to avoid its insulating effect.

4.elongated, often vascularized extremities to conduct body heat to the air.

Thermoregulation in Birds and animals25

`dThermoregulation In Humans26

The body must balance its heat budget.The core temperature of the human body is 37CHeat is gained:

by conduction from warm air surrounding the body

by the bodys metabolic activity which generates heat e.g. when muscle move

Heat is lost:

by conduction and radiation to cold air (or water)

by evaporation of sweat from the body surface (c.f. properties of water)

Humans can also affect their body temperature by changing their behavioure.g. wearing different clothes, seeking shade.Thermoregulation in Humans27

Advantages of warm bloodedness

nervesMore heat generatedLess water covers the skin.Less evaporationSkin arteries constrictLess blood to the skin. Less radiation & conduction of heat

Muscles of skin arteriole walls constrictSweat glands decrease secretionMusclesshiveringnervesCore body temperature 37CHypothalamusSweat glands increase secretionnervesMusclesreduce activityThermoreceptorsNEGATIVE FEEDBACKBlood temperatureBody loses heat31Maintaining the body temperature32

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Warm Blooded