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Temperature Regulation Maintaining Homeostasis with the Environment 1 Principles of Heat Balance • 2nd 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 H2O vary very little in temp. “Cold-blooded"; aka POIKILOTHERMS 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” – Fish changing depths in the water column to find a suitable temperature. – Desert animals burrowing beneath the sand during the day. – Insects that warm their flight muscles by vibrating them in place. – Dilating or constricting peripheral blood vessels to adapt more or less quickly to the ambient temperature. 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 HOMEOTHERMS • Metabolic heat (from glucose oxidation)= high energy expenditure • Warmer at center (organs) • The "Q10 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