Temperature Regulation

Maintaining Homeostasis with the Environment

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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

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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 wire3

"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.

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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).

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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

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Cutting energy losses

• Diurnal- vs- nocturnal • Hibernation – Slow down HR, metabolism,

breathing, etc. but constantly monitor external environment

• Fat Insulation- Seals • Fat Localization- Camels

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