Thermoregulation

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

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?

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.

Heat Exchange Between an Animal and its Environment See Fig. 41.15

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.

Lizard Behavioral Thermoregulation

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

Flipper of a seal or whale Heat Exchange in Appendages Cross-section: See Fig. 41.20 Leg of a bird or mammal Flipper of a seal or whale Which mechanism of heat transfer is operating here?

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.

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?

Temperature Homeostasis in Humans

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

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

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?

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?