Temperature Regulation Maintaining Homeostasis with the Environment 1

Principles of Heat Balance 2 nd Law of Thermodynamics: heat moves from a warmer body (heat source) to a colder body (heat sink) Enzymes usually only work with in 10 degrees Celsius temperature range before they lose their conformation (denature). Heating: – Conduction: The movement of heat – Convection: The movement of air or water in currents (rise as they warm) – Radiation: Transfer of energy in electromagnetic waves – Evaporation: gives off excess heat 2

Body size and the transfer of heat Transfer of heat is proportional to body surface exposed (surface area) Small animals "huddle" Emperor penguin huddle Birds huddle on a wire 3

"Cold-Blooded" –vs- "Warm Blooded" : "thermoregulation" Ectotherm- "changeable" body temperature Mostly aquatic - large bodies of H 2 O vary very little in temp. “Cold-blooded"; aka POIKILOTHERMSPOIKILOTHERMS They cannot control their own internal body temperature, but they are rarely actually "cold" and have other means to thermoregulate: – Snakes and lizards sunning themselves on rocks; “basking” Snakeslizards – Fish changing depths in the water column to find a suitable temperature. Fish – Desert animals burrowing beneath the sand during the day. Desert – Insects that warm their flight muscles by vibrating them in place. Insects – Dilating or constricting peripheral blood vessels to adapt more or less quickly to the ambient temperature.blood vessels 4

"Cold-Blooded" –vs- "Warm Blooded" : "thermoregulation" Endotherm- able to maintain a constant body temp. Land changes temp. rapidly, animals must adjust quickly. “Warm-blooded"; aka HOMEOTHERMSHOMEOTHERMS Metabolic heat (from glucose oxidation)= high energy expenditure Warmer at center (organs) The "Q 10 effect": the multiple by which a particular enzymatic reaction or metabolic process increases with each ten-degree Celsius increase in body temp. 5

The Thermostat The Hypothalamus: interprets information from thermoreceptors throughout the body. – Releases thyrotropin-releasing hormone (TRH) in response, which triggers the pituitary… Pituitary Gland – Releases thyroid-stimulating hormone (TSH), which affects the thyroid… Thyroid Gland – Releases Thyroxine (metabolic rate increases = temperature (body heat will then increase). 6

Regulatory Strategies: Regulating Rising Body Temp : Expose more body surface (heat loss) Evaporation from skin surface (perspiration) Panting Blood vessels in skin dilate (to release heat into environ.) Regulating Falling Body Temp : Blood vessels near skin constrict (to limit heat loss) Metabolism speeds up Shivering Hair stands up (erector muscles in skin) to trap warm air 7

Cutting energy losses Diurnal- vs- nocturnal Hibernation – Slow down HR, metabolism, breathing, etc. but constantly monitor external environment Fat Insulation- Seals Fat Localization- Camels 8