Lecture 12 10-14-10

Lecture 12 10-14-10 - Lecture 12 Lecture Controlled...

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Unformatted text preview: Lecture 12 Lecture Controlled Hypothermia: Hibernation, Estivation, & Daily Torpor Hibernation, Estivation Endothermy in Fish and Insects Endotherms in the Heat 14 October 2010 Homeothermy versus Poikilothermy Endothermy versus Ectothermy Diurnal variation in body temperature for the willow tit (a European chickadee (bird)) during the night at three different ambient temperatures. Endotherms exhibit varying degrees of temporal heterothermy, depending on species and environment. Temporal Heterothermy Hibernation, Estivation, and Torpor allow animals to escape energy demands of endothermy. Hibernation (long), torpor (short), and estivation (summer) are distinguished by differences in duration and season Golden-mantled ground squirrel Temporal Heterothermy – Controlled Hypothermia In torpid and hibernating birds and mammals, body temperature is allowed to drop close to Ta. Temporal Heterothermy – Controlled Hypothermia In torpid and hibernating birds and mammals, body temperature is allowed to drop close to Ta, resulting in substantial energy savings. At 15 C, energy expenditure of a torpid bat is ~40-fold less than an active bat. Controlled Hypothermia Torpor involves hypothermia for only part of the day Controlled Hypothermia Duration of daily torpor depends on food ration. On a 1/3 normal ration, pocket mice are torpid for 9 hours / day at 15 C. The energy savings allowed the animals to maintain body mass. Arousal is faster than descent into torpor because of enhanced oxygen consumption. Controlled Hypothermia Temperature regulation during torpor is not abandoned. Control of body temperature during temperature is relaxed and regulated in a manner that varies among species. The West Indian hummingbird readily enters torpor, but it will not allow its body temperature to drop below 18-20 C. Heat production is increased below Ta of 18 C. Endothermy in Fishes Thermal characteristics of water and respiratory physiology of fishes combine to make endothermy very difficult and rare in fishes. Endothermy in Fishes Thermal characteristics of water and respiratory physiology of fishes combine to make endothermy very difficult and rare in fishes. Endothermy in Fishes Large-bodied tunas generate heat in red muscle and conserve heat internally via vascular countercurrent exchange. Endothermy in Fishes Large-bodied tunas generate heat in red muscle and conserve heat internally via vascular countercurrent exchange. Heater Organ in Billfishes Brain Heater Heat Exchanger: Note close juxtaposition of arteries and veins. Heater Organ Cell: Note tight packing of mitochondria (5570% of cell volume) and sarcoplasmic reticulum (2530% of cell volume) and absence of contractile filaments in this modified muscle cell. Skeletal Muscle T Tubule Networks Heater Organ Summary of Brain Heater Organ • Modified muscle cell – Large SR, T tubule, and mitochondrial volumes – Loss of contractile filaments • ↑ sarcoplasmic Ca++ → contraction • Exceptional oxidative capacity • Extensive T tubule system indicates retention of neural control Endothermy in Insects Endothermic insects exhibit both temporal and spatial heterothermy. Thermoregulatory endothermic insects often exhibit thoracic homeothermy. Heat transfer from thorax to abdomen (or head) can be regulated. Endothermy in Insects Endothermy is tied to the mechanics and energetics of flight. Power output of flight muscles increases as temperature increases. Many large-bodied insects simply cannot fly unless they are warm. Pre-flight warm-up involves shivering. Endothermy in Insects Brood incubation by queen bee Heat is produced in thorax by shivering and transferred to abdomen by blood flow Endothermy in Insects Flight Muscle Regulated countercurrent flow controls heat transfer between thorax and abdomen Abdomen Heart Air Sac Thorax Venous Blood Countercurrent Blood Flow Diaphragm In Animal Physiology, by K. Schmidt-Nielsen Heat Balance Heat S + R + LE + G + C + M + s = 0 (S + Ri) + M = (G + C + Re + LE) + s Think about what this means. ● ● Endotherms: M normally > (S + Ri) M = G + C + Re + LE ● Heat Balance Heat In general, the distinction between endothermy and endothermy ectothermy depends on the relative magnitudes of M versus other terms in the heat balance equation. In extreme cases, heat balance in endotherms can be dominated by heat gain from solar radiation, leading to a positive value of s and an increase in Tb. This phenomenon has been noted in diurnal rodents, including antelope ground squirrels and cape ground squirrels. HEAT BALANCE HEAT Antelope Ground Squirrel Southwestern United States Heat balance on the desert surface is dominated by S. HEAT BALANCE HEAT Antelope Ground Squirrel Southwestern United States HEAT BALANCE HEAT Antelope Ground Squirrel Southwestern United States Behavior is almost always the first and most flexible line of defense. HEAT BALANCE HEAT Antelope Ground Squirrel Southwestern United Tb from 38 to By tolerating an increase in States 43 C, antelope ground squirrels extend their activity period on the hot desert surface. HEAT BALANCE HEAT HEAT BALANCE HEAT Cape Ground Squirrel Kalahari Desert Border of South Africa and Botswana Kalahari Desert Kalahari Border of South Africa and Botswana HEAT BALANCE Cape Ground Squirrel Tail Down Salivation ↑ Tb Tail Up Energy Metabolism and Temperature Regulation in Reindeer (Caribou) Regulation Ch. 10 in HW&A Winter acclimatization extends the TNZ by reducing thermal conductance and the lower critical temperature. Energy Metabolism and Temperature Regulation in Reindeer (Caribou) Regulation Ch. 10 in HW&A Thermal conductance is reduced in the winter in part because fur thickness is increased. Energy Metabolism and Temperature Regulation in Reindeer (Caribou) Regulation Ch. 10 in HW&A Regional heterothermy is an important component of the reindeer’s thermoregulatory strategy. Energy Metabolism and Temperature Regulation in Reindeer (Caribou) Regulation Differences in membrane fatty acid composition maintain membrane fluidity despite differences in temperature. ...
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