ThermoregulationBiology Stage 3Chapter 15Pages 317-324

YouTube clip

Thermoregulation (Bozeman Science 5 min)

https://www.youtube.com/watch?v=TSUCdLkI474&feature=youtu.be

KeywordsThermoregulationEctothermsEndothermsMetabolic heatHeat exchangeInsulation

◦Brown fatSurface area-to-

volume ratioTemperature

gradient

Physiological responses

PiloerectionVasodilationVasoconstrictionEvaporating

◦Sweating◦Panting

EctothermsAll animals, other

than birds and mammals, are ectotherms (‘outside heat’)

They do not generate their own heat but have a body temperature the same as that of the environment, whether it is hot or cold

They are often inactive during winter because their cells function so slowly at low temperatures

Ectotherm Ectotherms do alter

their behaviour to vary their internal temperature

They lie in the sun to warm up or burrow underground to stay cool

Some animals (some fish & insects) use the heat produced by their metabolism or by muscular activity (metabolic heat) to maintain a body temperature higher than the environment

EndothermsEndotherms (birds &

mammals) generate and maintain their own body heat

Maintaining body heat is called thermoregulation

If the environment is colder, the internal temperature is maintained by increasing heat production and reducing heat loss

If the environment is warmer, the internal temperature is maintained by decreasing heat production and increasing heat loss

EndothermsThermoregulation

involves:1. controlling

metabolic heat production

2. regulating heat exchange with the environment

Controlling heat productionHeat production is

controlled through increasing or decreasing metabolic activities

Metabolic heat can be generated by:Increasing muscle

activity (shivering)Increasing cellular

activity (brown fat)Increasing rates of

cellular metabolism

The hypothalamus is the regulatory centre in the brain

It signals to increase or decrease metabolic activities

It also regulates physiological responses to maintain homeostasis

Heat sensors or thermoreceptors in the body relay information to the hypothalamus

Regulating heat exchangeThe rate of heat

exchange with the environment depends on:

1. Insulation2. Surface area-to-

volume ratio3. Temperature

gradient between the body and the environment

4. Adaptive behaviours

INSULATIONFur & feathers Trap layer of warm air next

to skin Fur and feathers only good

insulators when dry Piloerection – tiny muscles

cause hair to lift away from skin increasing the thickness of the trapped air layer

Layer of fat Brown fat – hibernating

animals Large amount of

mitochondria

Regulating heat exchangeSURFACE AREA-TO-VOLUME

RATIO Smaller animals have a

larger surface area-to-volume ratio than larger animals

They therefore require relatively more food to maintain a higher metabolic rate

ADAPTIVE BEHAVIOURS Endotherms can vary their

behaviour to maintain optimum body temperature

TEMPERATURE GRADIENTRegulation involves: Circulatory changes

◦ Vasodilation◦ Vasoconstriction

Counter-current arrangements of blood vessels

Loss of heat through evaporation◦ Sweating◦ Panting

Countercurrent heat exchange

Rising body temperature

Falling body temperature

Feedback systems Negative feedback systems

have a number of common features:

The stimulus is the change in the environment

The receptor detects the change

The modulator is a control centre responsible for processing information

The effector carries out a response counteracting the effect of the stimulus (or change in the environment)

Behavioural responses to change in external temperature

Sensory receptor

Eff ector

External temperature <37oC or >37oC

Thermoreceptor Skin

Conscious area of brain

Somatic NS

Skeletal muscles

Behavioural response

Response

Changing heat gain or heat loss adjusts body temperature

stimulus

Regulation

Transmission

Response to high core temperature

Effector

Core temperature ˃37 o C Thermoreceptors

Hypothalamus

Surface blood vessels Sweat glands

Vasodilation Sweating

Reduced heat production & increased heat lossreturns core temperatureto normal

Stimulus

ModulatorControl centre

Response

Negative

feedback

Receptor

Response to low core temperature

Effector

Core temperature <37 o C Thermoreceptors

Hypothalamus

Surface blood vessels

Skeletal muscles Vasoconstriction

PiloerectionShivering

Reduced heat loss & Increased heat productionreturns core temperatureto normal

Stimulus

ModulatorControl centre

Response

Negative

feedback

Receptor