jimtrue.com : school : BSC2011 : CH 44: Thermal Regulation (Muscular, Respiratory, Circulatory)

Posted by Jim True on November 16, 2004 5:28 PM. Last Updated October 22, 2006 9:23 PM

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CH 44: Thermal Regulation (Muscular, Respiratory, Circulatory)

Thermal Regulation

• Section from Ch. 44, pp. 925-935.
• Regulator - an animal capable of controlling internal environmental conditions independently of external conditions.
• Conformer - animals whose internal environment is similar to their external environment.
• Regulation and conformity apply to responses to a wide variety of conditions. (these are factors that affect another condition, just like facultative and obligate.
• Two of the most significant are responses to temperature and the relative concentration of water inside and outside cells.
• Thermal(temperature) responses are found among all animals which the balance of water is much more significant in aquatic animals.
• Thermal regulation of chemical reactions is direct.
• Q₁₀ Effect - For every 10 degree C increase or decrease in temperature, there is a corresponding TWO-FOLD increase or decrease in metabolism. ie if the temperature changes from 40 to 50 degrees Celsius, the organisms metabolic rates is twice as fast; in the opposite direction, it is half as fast as it was before.
• This applies up to a maximum or down to a minimum lethal temperature at which enzyme activities drop to levels incapable of sustaining life.
• Heat gain or loss is assocated with four different processes:
1. Conduction - direct transfer of heat from one object to another. occurs via direct contact. e.g. Person becomes hypothermic if left in cold water.
2. Convection - Transfer of heat by the movement of air or liquid over the body surface. E.g. cooling breeze on your face.
3. Radiation - Emission of electromagnetic waves. Warm body radiates heat, e.g. sun, your face when you "blush".
4. Evaporation - Removal of heat from a liquid as it converts to gas, e.g. the cooling effect of sweating, which is enhanced by convection as a breeze blows across your sweat.
• Ectotherm - Animals that are temperature conformers, ie, their bog temperature and thus their metabolic activities are regulated by their external environment. All invertebrates, plus almost all fishes, amphibians and almost all reptiles.
• Ectothermic animals are reliant on environmental temperatures because their own metabolic rates are too low to generate much body heat.
• Ectothermic animals typically have lower activity levels and cannot sustain high levels of activity for long.
• An advantage to ectothermy is that food requirements are not as high to maintain metabolic levels.
• Endotherm animals that are temperature regulators, i.e., their body temperature is independent of their environment. (Usually warmer). Among vertebrates, all mammals and birds, plus some fishes and reptiles.
• There are invertebrate ectotherms as well, primarily among the flying insects, which generate heat through the flight muscles.
• Control of temperature ranges of the body for both endotherms and ectotherms falls into 4 categories:
1. Heat exchange across skin.. Usually associated with changes in the circulatory system.
• Vasodilation - Increase in blood vessel diameter brings heated blood near skin to allow cooling (blushing).
• Vasoconstriction - Decrease in vessel diameter that minimizes heat loss.
• Countercurrent heat exchange - Blood vessels passing outward from the core of the body (heated blood) lie parallel to blood vessels carry blood from the body surface inward (cooled blood). Heat transfers by conduction keeping the body core warm. This is found in many endotherms, including the few species of endothermic fishes (bluefin tuns, great white and mako sharks).
• Insulation of body (hair, feathers, fat layers) can greatly alter rate of heat loss/absorption.
2. Evaporative loss. - a Terrestrial adatation. Occurs through exhaled air (including panting) and across skin in animals that sweat.
3. Shifts in behavior.
• Moving into shade or jumping into water when body temperatures begin to rise to uncomfortable levels, e.g., basking reptiles.
• Hibernation - Metabolic shutdown when food supplies are not adequate to sustain active life, e.g., bears in winter.
• Migration - movement away from less favorable environemts, e.g., many birds.
• Shivering - involuntary behavior in which the muscles undergo rapid short contractions which generates extra heat.
• Movement - muscle activity itself increases body heat. "Pacing to keep warm".
4. Alteration of heat production from metabolism. Found only in birds and mammals, which are collectively referred to as homeotherms.
• These animals regulate their body temperature within a narrow range.
• Any time the environmental temperature is lower than the body temperature, there is a net loss of heat.
• Homeotherms compensate for this loss.
• They do so through a metabolic process called non-shivering thermogenesis, which increases the rate of heat production by mitochondria.

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