1. Thermoregulation
SBI4U Biology

2. Controlling Body Temperature
Homeothermy
“Same Temperature”
Endotherm
Mammals, Birds
Metabolically costly!
Large caloric intake
More habitat choice
Thermoregulation mainly physiological
Poikilothermy
“Colourful (Variable) Temperature
Ectotherm
Reptiles, Amphibians
Metabolically cheaper
Lower caloric intake
Limits habitats
Thermoregulation mainly behavioural
Controlling Body Temperature

3. Comparing the two

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

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

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

8. 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’…

9. Control Skin 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…

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

11. 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.

12. Dealing with 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.

13. Adaptations 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…

14. Adaptations for 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

15. Everyone’s a bit 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!