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Organismal Physiology Lecture No. 2.docx

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Western University
Biology 2601A/B
Tamsen Taylor

Organismal Physiology Lecture No. 2: Endothermy th Thursday September 13 , 2012 Introduction: -The explored temperature range for the environment may vary from -238°C (the surface of the moon) to 5,430°C (the Earth’s core). We, along with most of the organisms on Earth, live within the aquatic environment of the hydrosphere where there is a 4°C temperature range. The greatest range for oceanic organisms lies in places such as the deep sea vents and the polar seas. - As human beings are classified as homeothermic endotherms, and are thus responsible for regulating their body temperature, they (along with birds and other mammals) can live in higher temperature ranges that often fluctuate. E.g. Terrestrial temperatures. Homeothermic Endotherms: -As mentioned previously, mammals and birds can survive wide temperature ranges on Earth. Other ectothermic organisms such as turtles have a much slower metabolism in colder temperatures. What is remarkable is the fact that both mammals and birds have evolved their endothermic traits independently of each other; depicting physiological convergence as a solution to the thermal problem. What is important to note is that core/body temperature does not change in endothermic homeotherms. Effect Of Temperature On Endothermic Homeotherms: -This can be observed by examining an organism’s metabolic rate over an n range in temperature. In the thermoneutral zone metabolic rate is maintained at a very stable interval. The size of the zone varies for different homeothermic species. Large animals will exhibit a naturally large thermoneutral zone, while small animals, a small one. -Once within the thermoneutral zone, the organism will experience the modulation of insulation and blood flow. Outside the thermoneutral zone, species will exhibit increased energy consumption due to heat generation at colder temperatures and increased energy consumption due to heat loss at higher temperatures. Regulation of body temperature in homeotherms requires a set point for which there are many biological sensors like: the skin, spinal cord, back of the brain, hypothalamus, and scrotum (in males). Shivering Thermogenesis: -In Antoine Lavoisier’s experiment, a guinea pig’s thermal heat was measured from drops of water that trickled from a double-ice barrier calorimeter. The outer ice barrier protects the inner ice from environmental temperatures. -Because of water’s high heat capacity, a swimmer’s heat is lost through conduction and he/she find the need to shiver between swims. This shivering involves uncoordinated muscle contractions, performs no muscle contractions and uses ATP in order to generate heat for body temperature regulation. Non-Shivering Thermogenesis: -In an experiment, rats that were placed in 6°C environments shivered uncontrollably at first, but given time they ceased shivering a
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