Lecture 22: Thermoregulation and osmoregulation

1.   Four physical processes account for heat gain or loss (what are they and how do they work)

2.  Ectotherms have body temperatures close to environmental temperature;  endotherms can use metabolic heat to keep body temperature warmer than their surroundings

3.  Thermoregulation involves physiological and behavioral adjustments that balance heat gain and loss (what are they and how do they work)

4. Q10

•         Most biochemical and physiological processes are very sensitive to changes in body temperature.

•         The rates for most enzyme-mediated reactions increase by a factor of 2-3 for every 10oC temperature increase, until temperature is high enough to denature proteins.

•         This is known as the Q10 effect, a measure of the multiple by which a particular enzymatic reaction or overall metabolic process increases with a 10oC increase in body temperature.

•         For example, if the rate of glycogen hydrolysis in a frog is 2.5 times greater at 30oC than at 20oC, then the Q10 for that reaction is 2.5.

5. Ecto- vs. Endothermy

•         It is not constant body temperatures that distinguish endotherms from ectotherms.

•         For example, many ectothermic marine fishes and invertebrates inhabit water with such stable temperatures that their body temperatures vary less than that of humans and other endotherms.

•         Also, many endotherms maintain high body temperatures only part of the time.

•         In addition, not all ectotherms have low body temperatures.

•         While sitting in the sun, many ectothermic lizards have higher body temperatures than mammals.

•         Endothermy has several important advantages.

•         High and stable body temperatures, along with other biochemical and physiological adaptations, give these animals very high levels of aerobic metabolism.

•         This allows endotherms to perform vigorous activity for much longer than is possible for ectotherms.

•         Sustained intense activity, such as long distance running or powered flight, is usually only feasible for animals with an endothermic way of life.

•         Endothermy also solves certain thermal problems of living of land, enabling terrestrial animals to maintain stable body temperatures in the face of environmental temperature fluctuations that are generally more severe than in aquatic habitats.

•         For example, no ectotherm can be active in the below-freezing weather that prevails during winter over much of the Earth’s surface, but many endotherms function very well under these conditions.

•         Endotherms also have mechanisms for cooling the body in a hot environment.

•         Being an endotherm is liberating, but it is also energetically expensive, especially in a cold environment.

•         For example, at 200C, a human at rest has a metabolic rate of 1,300 to 1,800 kcal per day.

•         In contrast, a resting ectotherm of similar weight, such as an American alligator, has a metabolic rate of only about 60 kcal per day at 200C.

•         Thus, endotherms generally need to consume much more food than ectotherms of similar size - a serious disadvantage for endotherms if food is limiting.

•         Ectothermy is an extremely effective and successful “strategy” in many terrestrial environments.

6.   Water balance and waste disposal depend on transport epithelia (describe how this works)

7.  An animal’s nitrogenous wastes are correlated with its phylogeny and habitat (how so and why)

8.  Cells require a balance between osmotic gain and loss of water

9.  Osmoregulators expend energy to control their internal osmolarity;  osmoconformers are isoosmotic with their surroundings