1. Thermoregulation

2. Learning Objectives 2/13/08
Distinguish between the thermoregulators classified as endotherms and ectotherms, homeotherms, heterotherms, and poikilotherms
Describe the adaptive advantage(s) of endothermy
Discuss the 4 mechanisms utilized by land homeotherms to balance their heat budget
Discuss the roles of the hypothalamus in vertebrate temperature regulation
Compare and contrast some of the physiological mechanisms involved in acclimatization to new temperature ranges

3. Clarification on terms…
Ectotherm (ecto = “outside”) - An animal that derives body temperature from an external heat source.
Endotherm (endo = “inside”) - An animal that derives body temperature from internal heat production.
Note: These terms relate to the source of body heat, not whether the animals are capable of regulating body temperature.
Why is body temperature homeostasis important?
What must be true in order for an endotherm to maintain temperature homeostasis?

4. Poikilotherm (poikilo =“varied”) - body temperature approximates the ambient temperature. Not capable of controlling body temperature as ambient temperature varies. What is the adaptive advantage here?
Heterotherm (hetero = “different”) - regulates body temperature when active, but allows body temperature to fluctuate with the environment when inactive.
Homeotherm (homeo = “same”) - controls body temperature, keeping it relatively constant as ambient temperature varies.
These terms relate to whether or not the animal is capable of controlling body temperature.
Describe the advantage to temperature homeostasis from the fact that animal bodies are made mostly of water.

5. Heat Exchange Between an Animal and its Environment
See Fig

6. Body Temperature Regulation: Endotherm vs. Ectotherm
What anatomical & physiological
characteristics are common
among endotherms?
What other organ systems
are commonly well
developed in endotherms?
Are all ectothermic animals
correctly described as
“conformers”? Illustrate your answer with some examples.

7. Lizard Behavioral Thermoregulation

8. Behavioral and physiological mechanisms in Homeotherms
Relocation
Thermogenesis
Shivering
Non-shivering
Vasoconstriction/vasodilation
Evaporative water loss

9. Flipper of a seal or whale
Heat Exchange in Appendages
Cross-section:
See Fig
Leg of a bird or mammal
Flipper of a seal or whale
Which mechanism of heat transfer is operating here?

11. Control of Conductance by Regional Heterothermy
Cold-climate homeotherms can allow their appendages to cool to reduce heat loss.
Countercurrent heat exchange occurs between warm out-flowing blood in a central artery and cold in-flowing blood in surrounding veins.

12. Integumentary System in Thermoregulation
Organs of thermoregulation in the skin:
sweat glands
arrector pili muscle
vasodilation/vasoconstriction
What organ serves as the control center to regulate these organs?
Why are there both cold and hot
thermoreceptors in the body?

13. Temperature Homeostasis in Humans

14. Temperature Acclimatization
See p. 916
Molecular mechanisms
Make more enzymes (Why?)
Produce enzyme variants (Explain)
Alter cell membrane components (How?)
Produce cryoprotectants (“freeze tolerance”)
Produce stress-induced proteins
Behavioral mechanisms
Torpor
Hibernation (winter torpor)
Estivation (summer torpor)
Diurnal (daily, often nocturnal) torpor

15. The Fluid Cell Membrane
How does the behavior of the cell membrane change with temperature?
How does the chemical make-up influence this behavior?

16. Wood frog, Rana sylvatica (glucose acts as a cryoprotectant)
Wood frog in summer
Wood frog, frozen
The “winter” frog is in cardiac arrest, & has 65% of its body water frozen.
If ECF water freezes, what would happen to ICF water?

17. Heat-shock proteins protect and chaperone other proteins
Produced in response to various forms of stress: temp, hypoxia, pH, cancer, etc.
Protein clumps are seen in the
neurons of patients with Mad
Cow disease and Alzheimer’s
disease.
What cell function may be faulty in these disease processes?