TEMPERATURE Ranges from +45°C We’ll look at temperature effects on biological systems and adaptations with respect to: temperature regulation - endotherms adjustment to changing temperature adaptations to temperature extremes

Terminology Ectothermic (Cold-blooded, Poikilotherms) Endothermic (Warm-blooded, Homeotherms) Heterothermic Facultative Hyperthermy Nocturnal hypothermy

Heat Gain, Loss, and Storage Body heat = heat produced + (heat gained – heat lost) heat produced = metabolism heat gained = radiation, conduction, convection heat lost = radiation, conduction, convection, and evaporation

Conduction Transfer of heat between to objects in contact with each other Net flow from warmer to cooler May occur within same substance or between two phases

Convection Transfer of heat through a fluid by mass transport in currents Fluid can be liquid or gas Passive (“free”)—molecules that arise from heating surface Active (“forced”)—air moving over surface carrying away heat

Radiation Transfer of heat by electromagnetic radiation Emitted by all bodies above absolute zero Amt depends on 4 th power of absolute temperature ( o C + 273)

Evaporation Energy required to change liquid to a gas Biological systems— water to water vapor (g H 2 O = 585 cal) Water source can be external or internal Always results in heat loss

T body T amb VO 2 thermoneutral zone lower critical temp.

Within the zone of homeothermy, below the TNZ Increase H total by: voluntary muscular activity involuntary muscular activity - shivering non-shivering thermogenesis brown adipose tissue - has shunt to allow protons into mitochondria with- out making ATP other futile cycles Thermogenesis

Distribution of Brown Fat in Newborn Rabbit and Human Infant

Biochemical Events of Thermogenesis in Brown Fat Tissue