Thermoregulation

THERMOREGULATION

Control of body temperature

Overview:A) TEMPERATURE CONTROLB) ORGANISMS ARE CLASSIFIED BASED ON HEAT SOURCEC) BASAL METABOLIC RATED) THE HYPOTHALAMUS REGULATES BODY

TEMPERATUREE) ECTOTHERMIC ANIMALSF) ENDOTHERMIC ANIMALS: ADAPTATIONS TO EXTREME

CLIMATESG) ADVANTAGES & DISADVANTAGES OF ECTOTHERMY &

ENDOTHERMY

Range of environmental temperature inhabited by organisms:

90C in hot springs

-40C in the Arctic

Thermophilic bacteria

Most organisms, however, live in a narrow range of temperature from 10-30C

What must animals do to survive when ambient temperature

changes?

THERMOREGULATETHERMOREGULATE (control body temperature)

Thermoregulation is important: as cells can function only over a

narrow range of temperatures

if cells: cool below 0C: ice crystals form = damage some animals produce antifreeze

molecules

What about temperatures above 45 C?

ice crystal punctures cell wall

Action of antifreeze

Curious: Wood frog tolerates freezing

Wood frog in summer Wood frog, frozenWood frog, frozen

The “winter” frog is in cardiac arrest, & has 65% of its body water frozen.

All animals gain heat from two sources:

Metabolism of food Absorption of solar energy - directly or indirectly [see next slide]

2. absorption of solar energy - directly or indirectly from heat:

reflected from objects

convected from the warming of the ground

conducted from the ground

Three physical processes account for heat gain

ConvectionRadiation

Conduction

Four physical processes account for heat loss

Convection Radiation

Conduction

Evaporation

Evaporative cooling

Panting

Bathing

Sweating

Cats, rabbits and kangaroos spread saliva on their bodies. WHY?

To cool down as saliva evaporates.

Sweating

The skin

The skin of bullfrogs secretes more mucus when it is hot, allowing more cooling by evaporation

Core temperature

temperature of the tissues 2.5 cm beneath skin

determined by taking the oral /rectal temperature

Normal conditions:

extremities are cooler

When body is cold:

heat is diverted to the core region

Core temperature tends to refer to the temperature of:organs parts of the body that are well insulated

Why is it important that the core temperature remains constant?

To keep vital organs warm

The enzyme systems must operate in optimum conditions

Overview:

A) TEMPERATURE CONTROLB) ORGANISMS ARE CLASSIFIED BASED ON HEAT SOURCEC) BASAL METABOLIC RATED) THE HYPOTHALAMUS REGULATES BODY TEMPERATUREE) ECTOTHERMIC ANIMALSF) ENDOTHERMIC ANIMALS: ADAPTATIONS TO EXTREME

ENDOTHERMY

For many years, physiologists classified animals according to

whether:

they maintained a constant body

temperature

they maintained a constant body

temperature

their body temperature fluctuated with environment

homeotherms regulate body temperature

about a set point

homeotherms regulate body temperature

about a set point

poikilothermsallowed their body

temperature to conform to the environment

poikilothermsallowed their body

temperature to conform to the environment

Problem with this terminology:

a poikilotherm in an environment with a stable temperature (e.g. many deep-sea fish species) has a more constant body temperature than some homeotherms

These limitations in classifying animals in this way, led to another view based on how body heat is generated :

Endotherms (internal source)

Ectotherms (external source)

Endotherms animals that use

metabolism to generate body heat and maintain their temperatures above the ambient temperature

birds and mammals

Ectotherms animals with a

relatively low metabolic rate, do not use metabolism to produce heat and have a body temperature that conforms to the ambient temperature

all non-vertebrates, fish, amphibia and reptiles

The evolutionary advantage of being endothermic :

is that it gives much more environmental independence

it is no coincidence that the most successful animals in the extremes of temperatures found in:

deserts at the poles

are mammals and birds

Ectotherms and endotherms respond differently in metabolic

chambers

Conclusion:

The lizard:apparently cannot regulate its body temperature or metabolism independently of environmental temperature

The mouse:regulates its body temperature by increasing its metabolic rate, which increases its production of body heat

The laboratory conclusion that the lizard cannot regulate its body

temperature may be tested by: 1. releasing the lizard

in its desert habitat.2. measure its body temperature as it goes in its normal behaviour as the air temperature can change by 40 C in a few hours

Unlike what was observed in the metabolic chamber, the body temperature of the lizard is at times considered different from the environmental

temperature

Conclusion the lizard can regulate its body temperature quite

well by behavioural mechanisms rather than by internal metabolic mechanisms

in the laboratory experiment, the lizard could not use its thermoregulatory behavior, but in its natural environment it could move to different places to alter the heat exchange between its internal and external environments

Behavioural thermoregulation is NOT the exclusive domain of ectotherms

it is also the first line of defence for endotherms

behavioural thermoregulation is widespread in the animal kingdom

given the option, most animals select the thermal

microenvironments that are best for them

Three Types of Thermoregulation Mechanisms:

1. Behavioural 2. Physiological3. Structural

BEHAVIOURAL : Conscious action is taken e.g. altering posture, orientation, and/or microclimate to regulate body temperature.

Chicks seek shade.

HuddlingHuddling

Lie in water

Behavioural mechanismsReorientation Wallowing

(lie in water)Shelter

Thermal gaping Body raisingColour changes

PHYSIOLOGICAL: Changes occur from within the organismSweatingVasodilation / vasoconstrictionLowering heart rateRaising of hair

STRUCTURAL / ANATOMICAL : physical features of the organism

Dewlap in Zebu cow

Large ears to radiate

Homeotherm

an animal that is able to maintain a fairly constant body temperature independently of the environmental temperature by using physiological mechanisms

Poikilotherm

an animal that is unable to maintain its body temperature within narrow limits using physiological mechanisms, although many do so using behavioural mechanisms

Organisms from different phyla have evolved numerous adaptations for controlling body temperature. One of the most basic distinctions is that between ectotherms and endotherms.

a) Name TWO sources of heat that contribute to the

body temperature of animals. (1)b) Complete the following table by giving one example

of each thermoregulatory mechanism in mammals. (3)

Question [MAY, 2003]

Thermoregulatory mechanism

Example

StructuralElephant: large ears to lose heat

BehaviouralRabbits enter burrow on a hot day

PhysiologicalSweating on a hot day

c) Complete the following table by giving one example of each thermoregulatory mechanism in mammals.

Explain the following observations:

a. Mammals and birds generally hunt reptiles and amphibians shortly after dawn. The percentage of successful hunts decreases sharply during the late morning and afternoon. (2)Reptiles & amphibians are ectotherms and move slowly early in the morning. Easy to catch. Move quicker later on as their body temperature rises.

Explain the following observations:

b. A number of animals hibernate during the winter months. (2)

Do not find enough food to meet the demands of their high metabolic rate.

c. The Sandhill Snail (Theba pisana), a native of the Maltese Islands, spends the summer months attached to the upper parts of the stalks of tall vegetation. (2)

Ground absorbs heat. Temperature is higher near the ground.Thus snail positions itself at a cooler temperature.

Both ectotherms and endotherms control blood flow to the skin

just as behavioural thermoregulation is not the exclusive domain of ectotherms, physiological thermoregulation is not the exclusive domain of endotherms

both can alter the rate of heat exchange between their bodies and their environments by controlling the flow of blood to the skin

VasodilationVasoconstriction

Cold day Hot day

Marine iguana:- basks on black lava rocks- maintains a temperature of 37°C

- spends a considerable time in the sea (25°C) to feed on seaweed

How does the Marine Iguana avoid heat loss when diving?

Reduces heart beat (bradycardiabradycardia).Less blood flow to the skin

In Seals: as part of the dive reflex, blood is diverted away

from the skin to the core organs, thus saving energy that would otherwise go into re-warming cooled blood.

Some ectotherms produce heat

Many insects: flight muscles must reach 35 - 40C before flightthese temperatures must be maintained during flight, even at air temperatures around 0C

Honeybees regulate temperature as a group

Honey bees survive harsh winters by: clustering together shivering to generate metabolic heat

Some reptiles use metabolic heat production to raise their body

temperatures above the air temperature

the female Indian python protects her eggs by coiling her body around them

if the air temperature falls: she contracts the muscles of her body wall to generate heat

Some fish elevate body temperature by conserving

metabolic heat

“Cold” fish: great heat losses at gills.

Warm blood is in contact

with cold water

Bluefin tuna & great white sharks maintain a high body temperature!!

The bluefin tuna & great white sharks, can maintain temperature differences as great as 10 - 15C

between their bodies and the surrounding water. How is this possible?

Generate heat from their powerful swimming muscles

Ability of these “hot” fish to conserve heat

Heat is conserved by a countercurrent heat exchanger

Arterial blood flowing into the

muscles is warmed by venous blood

flowing out of the muscles.

Bluefin tuna:large, rapidly

swimming fish

Countercurrent heat exchangeoccurs between:

warm out-flowing blood in a central artery and

cold in-flowing blood in surrounding veins

Cold-climate homeotherms can allow their appendages to cool to reduce heat loss

Flipper in dolphin / seal

Air: - 16 C

Overview:A) TEMPERATURE CONTROLB) ORGANISMS ARE CLASSIFIED BASED ON HEAT SOURCEC) BASAL METABOLIC RATED) THE HYPOTHALAMUS REGULATES BODY TEMPERATUREE) ECTOTHERMIC ANIMALSF) ENDOTHERMIC ANIMALS: ADAPTATIONS TO EXTREME

ENDOTHERMY

changing their rates of heat production, measured as

metabolic rate

Endotherms respond to changes in environmental

temperature by

Thermoneutral zone

Within the thermoneutral zone: the metabolic rate of endotherms is low and independent

of temperature

Basal Metabolic Rate (BMR)

the metabolic rate of a resting animal at a temperature within the thermoneutral zone

BMR refers to the minimum amount of energy that the body requires to complete its normal functions when at rest mentally and physically more than 12 hours after the last meal

Factors that regulate the rate of energy release:

2. Hormones: Thyroxine: increases metabolic rate: effects are

long term Adrenaline: produces short-term increases in

metabolic activity

1. Environmental temperature People living in cold climate have higher BMR

compared to people living hot climate.

3. Gender:women have lower BMR than men 10-12% lower than those of men of same age, height and weightReason: more muscle tissues in men

Males 1,600 -1,800 kcal per day

Females 1,300 - 1,500 kcal per day

4) Age:

highest BMR: 1-2 yrs

BMR accelerates during puberty

BMR is reduced

gradually

BMR is reduced

gradually

5. Physical activity (PA):Sedentary lifestyle leads to lower BMR because it leads to less active muscles.

6. Diet: Starvation or serious abrupt calorie-reduction can dramatically reduce BMR by up to 30%

Restrictive low-calorie weight loss diets can cause the BMR to drop as much as 20%

7. Body Surface Area:

A tall thin person will have a higher BMR than a shorter, fatter person

BMR also increases in pregnant women

BMR of an endotherm is about 6X greater than of an ectotherm of

the same :

size body temperature

Heat for thermoregulation is created through:

Shivering Nonshivering nonshivering

thermogenesis occurs in brown fat

Numerous mitochondria = brown colour

Heat released

Heat + ATP released

What happens to the BMR as the animal becomes smaller?

shrewshrew

ENDOTHERMY

HEAT GAIN HEAT LOSS

Balance in heat gain and heat loss

The hypothalamus: monitors the temperature of the

blood flowing through it receives information regarding

changes in external temperature from thermoreceptors

two types of thermoreceptors: hot cold

Hypothermia is a reduction in the core temperature below normal

results from:- a natural turning down of the thermostat- traumatic events e.g. starvation, exposure,

serious illness- treatment by anaesthesia

Animals can save energy by turning down the thermostat

Foil Blanket

Many species of birds & mammals use regulated hypothermia

as a means of surviving periods of cold and food scarcity

some become hypothermic on a daily basis:

e.g. hummingbirds

Endotherms can reduce:

1.metabolic rate

2.body temperature

to produce a state of

dormancy called

TORPOR

to produce a state of

dormancy called

TORPOR

Torpid mammals

is the deliberate lowering of the set pointTorpor

Torpor in Rufus hummingbird Normal body temperature: 39°C Lowered to 12-17°C at night when nectar is scarce

Normal consumption at night if set point is 39°C: 0.24g fat

Consumption in torpor: : 0.02g - energy savings of about 90%

Why is the set point lowered?

When food needed to meet demands of

thermoregulation is not present.

Long-term torpor in endotherms is: HIBERNATION (low food) AESTIVATION (heat or drought)

Torpor can be: Daily bats torpor during the dayhummingbirds at night

Daily bats torpor during the dayhummingbirds at night

Long-term can last for days or weeks in summer or winter

What happens to the body temperature in hibernation?

Certain squirrels show prolonged torpor with brief arousals in winter

How is periodic arousal fuelled?

By burning brown fat.

Do bears hibernate? bears drop body temperature slightly and

enter a winter sleep large mammals have too large a mass to

allow rapid cooling

Bears in winter sleep: metabolism is near normal are easily aroused do not defecate, urinate, drink

occurs also in ectotherms Torpor

One species of burrowing frogs can survive for years buried in mud without food and water.

Overview:

ENDOTHERMY

The majority of animals are ectothermic : Their activity: is determined by the

environmental temperature

Metabolic rate:is relatively low

Lack mechanisms for conserving heat

(no body covering)

Do attempt to regulate their temperatures within broad limits:

using mostly BEHAVIOURAL methods

The main sources of heat gain are:

Absorption of solar radiation

Contact with the air and ground

The amount of heat absorbed depends upon:

the colour of the organism

orientation to the Sun and surface area exposed

COLOUR: temperature influences pigmentation on grasshoppers

DARK at a low

temperature

LIGHT at a high

temperature

Parallel to incoming sun

Orientation to the sun

Perpendicular

Which position is ideal for

lizard to warm up?

Orientation to the sun: a form of behavioural mechanism

Perpendicular

More surface area exposed

Reptiles:Crocodiles regulate their body temperature on land by: Varying orientation

Thermal gaping

Moving into the water if the temperature becomes too high

Lizards regulate body temperature by:a) burrowingb) pull back ribs to reduce body surface area when

the temperature becomes highc) eye bulgingd) thermal dancing

Thermal dancing

When the sand is hot, the lizard lifts opposite pairs of feet alternately so

that they can cool in the air.

Lizards regulate body temperature by:

e) eliminating urine from the cloaca [cloaca – terminal region of gut of most vertebrates into which kidneys and reproductive ducts open]

Cloaca in birds.

Overview:

ENDOTHERMY

1) having a high metabolic rate2) controlling efficiently heat loss from the body surface

How do they conserve heat?

Birds and mammals maintain a constant body temperature by :

Whale blubber

Subcutaneous fat A layer of fur / feathers

act as Insulators

Featherless Chickens

Israel: Israel: May 22, 2002May 22, 2002

Genetically modified chickens – farmers save money – no need to ventilate to keep chickens cool

Blubber & Fur act as Insulators:

In which case can the insulation be

bypassed?

Blubber

Fur thickness increases in winter:

Fur in a camel:reflects sunlight & so heat

Camels have very long legs:

to hold their body far from the hot sand

to enable air to flow under the body and therefore cool them

Fur insulates the camel

Control group(Unclipped fur)

Experimental group(Clipped fur)

Knut and Bodil Schmidt-Nielsen and their colleagues from Duke University observed that the fur of camels exposed to full sun in the Sahara Desert could reach temperatures of over 70°C, while the animals’ skin remained more than 30°C cooler. The Schmidt-Nielsens reasoned that insulation of the skin by fur may substantially reduce the need for evaporative cooling by sweating. To test this hypothesis, they compared the water loss rates of unclipped and clipped camels.

EXPERIMENT

RESULTS

Removing the fur of a camel increased the rateof water loss through sweating by up to 50%.

The fur of camels plays a critical role intheir conserving water in the hot desertenvironments where they live.

CONCLUSION

Three factors limit heat loss:-

Rate of evaporation from the skin

Amount of insulation

Rate of blood flow between the body core and skin

If the temperature rises, the blood vessel dilates (gets bigger).

This means more heat is lost from the surface of the skin

VasodilationVasodilation

If the temperature falls, the blood vessel constricts (gets shut off).

This means less heat is lost from the surface of the skin

VasoconstrictionVasoconstriction

The total heat production of endotherms depends upon the:

Volume of the body

The rate of heat loss depends upon the:

Surface area

The bigger the Surface Area : Volume ratio is, the faster heat will be lost.

Animals living in:

Cold regions tend to be large e.g. polar bears, whales Hot climates are

generally smaller

Large SA: VolKangaroo rat

Small SA:Vol

Exceptions exist, but animal must be adaptede.g. small mammals in temperatetemperate or arctic arctic regions:-

a) large appetite to maintain a high metabolic rate

b) small extremities such as small ears to reduce heat loss

c) hibernate in winter

e.g. small mammals in temperatetemperate or arctic regions:-

Ground squirrel hibernating

Exceptions exist:

Elephant in warm climates

Small mammals in Small mammals in temperate or arctic temperate or arctic

regionsregions

Adaptations shown by small animals in hot climates

Being Being nocturnalnocturnal

Adaptations shown by small animals in cold climates

Being diurnalBird migration

Adaptations shown by small animals in cold climates

Have short extremities

Ectotherms and endotherms use behaviour to regulate

body temperature

Behavioural thermoregulation Includes:- Change in posture- Orient to the sun- Move between still air and

moving air- Huddling / Curling up- Burrowing- Humans select appropriate

clothing and heat or cool their buildings

Change in posture

A handstand-like position that some dragonflies assume to prevent overheating.

The abdomen is raised until its tip points at the sun, minimising the surface area exposed to solar radiation.

Birds orient wings to

incoming sun

Orientation to the sun

Moving between shade and sun

Sheep keep cool in the shade.

Huddling

Penguins huddling

Lone penguin: great heat loss

Huddling

Huddling in a group BUT curling when alone

BurrowingAir temperature may fall to -50C but in burrows the temperature seldom drops below -5C.

Weasel in burrow.

ENDOTHERMY

Costs of Not Thermoregulating

Predation riskPredation risk Reduced foragingReduced foraging Reduced performanceReduced performance

Disadvantages of ectotherms Activity restricted to certain hours or

habitats (temperate & tropical latitudes). Activity restricted to brief bouts. Rapid exhaustion. Sluggish until warmed by the sun. Immune system does not work so well at low

temperatures.

Disadvantages of endotherms

Require MUCH food (80 – 90% of metabolic energy is used to thermo regulate).

Require CONTINUOUS supply of food, water & oxygen.

Advantages of endotherms Always ready for action; can be active at a variety of

times of day and in a wide range of habitats. Their work capacity is many times that of

ectotherms.

Not greatly affected by outside temperatures. Muscles provide endurance power; capable of

sustained high activity.

Advantages of ectotherms:

Low metabolic rate, so can occupy habitats with low or sporadic food supply (many ectotherms can go for months without food).

Have “sprint” speed. Endure shortages of food, water or oxygen.

What is the advantage for mosquito eggs, larvae & pupae to develop in

water rather than on land?

Cooler!!

Two species of Two species of Lepus Lepus adapted to live at adapted to live at different temperatures. Explain how.different temperatures. Explain how.

Refer to:

SEP, 2003 Paper 3 [graph plotting]

MAY, 2013 Paper 2 [comprehension]

Short Questions

Dewlap Hump of fat White colour

1. Explain how three features, visible in the drawings, may enable the zebu cow to be better adapted to being able to withstand high temperatures.

Dewlap:Increases surface area for

heat loss.

Hump of fat Fat is localised in one area.

Heat loss is possible from the rest of the body.

White colour

Cow does not absorb much heat.

2. Consider the following statements:a) Penguins huddle together during the cold Antarctic

winter, changing places with one another from time to time.

b) When a dog is feeling hot it pants with its large wet tongue hanging out.

c) A robin appears to be larger in winter than in summer.

d) African tribesmen living in cold mountain regions are much more stockily built than those of the warmer lowlands.

Stockily built

i) Explain how the behaviour of (1) the penguins and (2) the dog contribute to the maintenance of a constant body temperature.

Penguins reduce surface area for heat loss. Dog cools as saliva evaporates.

ii) Mammals living in very hot desert conditions do not display the same panting behaviour as the dog. Why not?To avoid water loss.

iii) Account for the seasonal difference in the appearance of the robin.Layer of insulation is thicker when feathers are fluffed to reduce heat loss.

iv) Suggest a reason for statement (d). Stockily built in cold climates to have a smaller surface area for heat loss and a larger volume to generate heat.

4. Use your knowledge to explain the following:

Predators generally hunt lizards in the early morning. (5 marks)

Lizards are ectotherms.Have a low body temperature and metabolic rate

until they warm up.Sluggish early in the morning and thus easy to

catch.

Essay Titles1. How do terrestrial vertebrates regulate their body temperature?[1978]

2. Explain what is meant by HOMEOSTASIS. With reference to EITHER temperature regulation in a mammal, OR to the control of blood glucose level, illustrate the principle of negative feedback. [1988]

3. Ectothermal organisms cannot control their body temperature. Discuss. [MAY, 2000]

4. Write a comparative account on thermoregulation in ectotherms and endotherms. [MAY, 2009]

Mechanisms for thermoregulation• Insulation

- Fur- Hair- Feathers- Fat- Blubber

• Evaporative cooling- sweating, panting, bathing

• Shivering• Nonshivering thermogenesis & brown

fat• Circulation adaptations

- Countercurrent exchange- Vasodilatation (cooling)- Vasoconstriction (heat conservation)

• Behavioural responses

So cool!!So cool!!

THE ENDTHE END

Thermoregulation

Technology

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