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On the utility of a mechanistic approach to physiology - the evolutionary origin of endothermy
Published on April 27, 2016 33 min
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My name is John Torday. I'm a Professor of evolutionary medicine at UCLA. This lecture is entitled "The Evolutionary Origin of Endothermy" as Integrated Physiology.
The evolution of endothermy is considered to be a watershed in vertebrate history, yet it is poorly understood at best. It has arisen in mammals and birds and is conventionally thought of as having occurred as a consequence of muscle generating heat. The aerobic capacity model has gained acceptance, according to which selection for metabolic demand has led to increased metabolism and accidentally, to endothermy as a consequence. However, the cellular molecular approach to the evolution of visceral organs in adaptation to land, provides a mechanistic continuum of adaptive events, both ontogenetically and phylogenetically, offering a novel testable and refutable approach to how and why endothermy evolved.
It should be kept in mind that birds and mammals are both endothermic and share a number of physiologic characteristics. Highly specialized lungs with expanded pulmonary capacities and ventilation rates. Fully separated pulmonary and systemic circulatory systems, expanded cardiac output. The last two traits of the direct result is the duplication of the beta-adrenergic receptor during the water land transition. These physiologic traits fostered the highly specialized lungs.
Based on the cellular molecular approach to endothermy, phylogenetically, ontogenetically, and functionally, endothermy can be understood as a consequence of interactions between the respiratory, neuroendocrine and metabolic systems during the water to land transition. The effect of adrenaline on endothermy is consistent with the duplication of the beta-adrenergic receptor during the water-land transition fostering the independent regulation of blood pressure in the lung and non-lung circulations. Independent regulation of blood pressure in the lung and non-lung circulation, complimented by the role of the beta-adrenergic receptor in adrenaline stimulated fatty acid release from fat pads causing increased metabolic rate.