Lecture+5-endothermy+2023.pdf

Biology 2601: Organismal Physiology Endothermy 1 Endothermic Homeotherms Maintain a high and stable body temperature (Tb) using internal heat High basal metabolic rate (cellular, tissue and whole animal levels). Mechanisms to retain heat such as insulation (fur, feathers, blubber) 2 Ectotherms...

Biology 2601: Organismal Physiology Endothermy 1 Endothermic Homeotherms Maintain a high and stable body temperature (Tb) using internal heat High basal metabolic rate (cellular, tissue and whole animal levels). Mechanisms to retain heat such as insulation (fur, feathers, blubber) 2 Ectotherms vs endotherms 3 A physical model Power required to maintain a heated object at a set point of 37 °C: P = C(Tset – Ta). Zero power when air temperature is 37 °C. Power (W) C = |slope| Air Temperature (°C) 37 4 A physical model Insulation reduces conductance and reduces power required to maintain the set point temperature. Power (W) C = |slope| Air Temperature (°C) 37 5 Add biology Endothermic homeotherms have a minimum energy expenditure (BMR) and deviate from the physical model. Power (W) C = |slope| Air Temperature (°C) 37 6 The Scholander Curve Below the TNZ, M = C(Tb – Ta). Within the TNZ, C changes and MR constant. Wilmer, Stone, Johnston. 2000. Environ. Physiol. of Animals 7 Changing conductance Vasomotor responses (vasoconstriction, vasodilation, anastomoses) 8 Changing conductance Pilomotor or ptilomotor responses www.mnn.com 9 Changing conductance Postural changes or huddling (crèche) 10 Changing conductance Regional heterothermy through countercurrent exchange 11 Changing conductance Cold adapted animals have lower thermal conductance than tropical animals 12 Seasonal acclimatization to cold tolerance can be achieved by metabolic adjustment or through changes in pelage (insulation) 13 Excess heat production Shivering is caused by non-synchronous muscle contractions to generate heat. 14 Excess heat production Non-shivering thermogenesis is the production of excess heat by futile cycles. E.G. the H+ leak across the inner mitochondrial membrane mediated by uncoupling proteins. H+ returns, ATP synthesized Substrate broken down, H+ pumped out 15 Excess heat production Non-shivering thermogenesis is the production of excess heat by futile cycles. E.G. the H+ leak across the inner mitochondrial membrane mediated by uncoupling proteins. H+ returns, Heat wasted Substrate broken down, H+ pumped out 16 Excess heat production Brown fat is specialized for non-shivering thermogenesis 17 Brown vs white fat Ahajournals.com 18 Heat Loads At and above the UCT conductance is maximal. Above the UCT excess heat can be stored by increasing Tb or lost by evaporation. e.g. heat storage in squirrels and camels. 19 Heat Loads At and above the UCT conductance is maximal. Above the UCT heat can be stored by increasing Tb or lost by evaporation. e.g. evaporation by sweating, licking, panting, gular flutter. 20 Endothermy in “ectotherms” Regional endothermy in skunk cabbage (and other Araceae) Spadix 21 22 Thermogenesis in aroids • Not inhibited by CO, cyanide, or azide • Alternative oxidase pathway Alternative oxidase in the ETC TZMM Fig 11.8 Regional endothermy in flight muscles of moths 24 Why fish are ectotherms • Fish can generate heat, but they have problems keeping it • Surrounded by thermally-conductive water (25 X more than air) 25 Fish gills act as a heat sink CPU Heat Sink Fish Gills 26 27 Regional endothermy in tuna: temperature gradients in 19°C Water 23 °C 29 °C 31 °C 27 °C 23 °C 19 °C 28 A rete mirabile retains heat (and other things) in a small region Water From heart/core = arterial blood Back to heart/core = venous blood Water e.g. Counter-current heat exchanger 29 Area of Rete HWA Fig. 10-46 30 Blue fin tuna red muscle temperature is elevated above water temperature 31 Regional endothermy evolved in bony fishes on at least three separate occasions HWA Fig 10-47 Why regional endothermy in fish? 32 • To allow long migration through water of different temperatures? • To allow better performance as a predator chasing prey into colder water? • Improvements in power output of muscles or vision (in bill fishes)?