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 Earths
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 animals
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