thermoregulation
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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
CLIMATESG) ADVANTAGES & DISADVANTAGES OF ECTOTHERMY &
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
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
Rec
tal
tem
per
atu
re
(oC
)
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
fur
Large ears to radiate
heat
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.
(3)
Question [MAY, 2003]
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.
Question [MAY, 2003]
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
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!!
BUT
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
CLIMATESG) ADVANTAGES & DISADVANTAGES OF ECTOTHERMY &
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
highest BMR: 1-2 yrs
BMR accelerates during puberty
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
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
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
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
NO
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:
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
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:
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
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)
4
3
2
1
0
Wat
er lo
st p
er d
ay(L
/100
kg
body
ma
ss)
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
Rate of evaporation from the skin
Amount of insulation
Amount of insulation
Rate of blood flow between the body core and skin
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.
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
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!!
Larva
Pupa
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.
Question [MAY, 1996]
c) A robin appears to be larger in winter than in summer.
Question [MAY, 1996]
d) African tribesmen living in cold mountain regions are much more stockily built than those of the warmer lowlands.
Question [MAY, 1996]
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.
Question [MAY, 2005]
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
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