Thermoregulation SBI4U Biology

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

Comparing the two

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

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

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

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 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 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: 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 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 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 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 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!