ThermoregulationThermoregulationSBI4U Biology

Controlling Body TemperatureControlling Body Temperature

Homeothermy “Same

Temperature”EndothermMammals, BirdsMetabolically costly!Large caloric intakeMore habitat choiceThermoregulation

mainly physiological

Poikilothermy“Colourful (Variable)

TemperatureEctothermReptiles, AmphibiansMetabolically cheaperLower caloric intakeLimits habitatsThermoregulation

mainly behavioural

Comparing the twoComparing the two

Physiology of Physiology of HomeothermyHomeothermy• Hormones, such as thyroxine• Nervous control, including peripheral nerves• Receptors in skin & within body• Hypothalamus is coordinator of thermoregulation, as well as a receptor

Not so simple, is it? And it’s all automatic…

Shivering:Shivering:• An autonomic nervous response• Rapid muscle contractions generate heat• costs us some energy, though, so not a long term solution.

Goosebumps:Goosebumps:• Erector pili muscles try to raise our hair• Raised hair traps air as a layer of insulation, warmed by body heat• Great for furry mammals, not so much for the ‘Naked Ape’…

Control Skin Control Skin blood flow:blood flow:• Pre-capillary Sphincter muscles stop blood flow, to avoid heat loss.• Vasoconstriction• If prolonged, the muscles relax (Vasodilation) to prevent tissue damage.• Appendages most affected: ears, nose, feet, hands…

Adaptations Adaptations to cold:to cold:• Behavioural postures• Shorter limbs & extremities• Thicker fur, fat…• Hibernation: long term solution to save a LOT of metabolic energy• Seasonal migrations, too.

Losing Heat:Losing Heat:• Radiate it out of your skin – vasodilation of capillaries will increase blood flow & heat loss.• Evaporate it off of your skin – nerves stimulate sweating• Evaporate it off your tongue – dogs & birds pant.

Dealing with Dealing with Heat:Heat:

• Avoiding the energy cost by estivation & torpor• Torpor is a sleep-like state, where body temperatures are allowed to fluctuate more than usual• Birds, small mammals, land snails, toads.

Adaptations Adaptations for Heat:for Heat:• Long limbs & extremities• Turbinate bones in nasal cavity are numerous, thin, & covered in moist tissues for evaporative heat loss.• Behavioural: postures, being nocturnal…

Adaptations for Adaptations for Heat:Heat:

• “Rete Mirabile”: Latin for “miraculous net”• Arterial blood warms the Venous blood in cold, and bypasses the ‘net’• In heat, blood freely flows into the ‘net’, heat lost.• Mostly mammals• Countercurrent Heat Exchange

Everyone’s a bit Everyone’s a bit different…different…• Like many other homeostatic responses, thermoregulation is also influenced by: • genetics• acclimation• However, a range of tolerance exists; exceeding it is harmful: hypothermia & hyperthermia kill!