Endothermy & Thermoregulation

1. Endothermy & Thermoregulation • Modes of Increasing Heat Production • below thermoneutrality (thermogenic processes) 1) Shivering: high-frequency, relatively uncoordinated contraction of skeletal muscles; convert chemical to thermal energy

2. Endothermy & Thermoregulation • Modes of Increasing Heat Production • below thermoneutrality (thermogenic processes) 2) Nonshivering thermogenesis (NST): • increase ion pumping by Na+-K+ active transport pump in cell membranes • frees catabolism to permit oxidation of food reserves with immediate release of heat

3. Endothermy & Thermoregulation • Modes of Increasing Heat Production • below thermoneutrality (thermogenic processes) 2) Nonshivering thermogenesis (NST): • best site = brown adipose tissue or brown fat • brown fat has: large # mitochondria large # blood vessels

4. Modes of Increasing Heat Production • below thermoneutrality (thermogenic processes) 2) Nonshivering thermogenesis (NST): • brown fat = hibernating gland (misnomer) • brown fat prominent in: • cold-acclimated or winter-acclimated adults, especially small to medium body size • hibernators • neonates

5. Modes of Increasing Heat Production • below thermoneutrality (thermogenic processes) 3) Activity • increase heat production in large but not most small mammals • shivering (not NST) is inhibited by activity

6. Modes of Increasing Heat Production • below thermoneutrality (thermogenic processes) 4) Regional Heterothermy – common to all mammals • Appendages = poorly insulated; used to shunt heat during activity or prevent heat loss (via countercurrent exchange)

7. Modes of Increasing Heat Production 4) Regional Heterothermy Countercurrent heat exchange: mechanisms allowing blood to flow to coldest part of extremity without loss of heat; related to vaso-dilation/constriction - close arrangement of arteries & veins

8. Modes of Increasing Heat Production 4) Regional Heterothermy Countercurrent heat exchange: e.g., human arms, mammal legs, dolphin flippers, rodent tails, lagomorph ears, foot pads of wolves - vascular arrangement varies in complexity

9. Modes of Increasing Heat Production 4) Regional Heterothermy Countercurrent heat exchange: rete mirabile (wonderful net): complex network of veins & arteries; increased efficiency in thermoregulation e.g., arms of sloths; brains of African antelopes

10. rete mirabile

11. Regional Heterothermy & Performance

12. Responding to High Heat Loads 1) first defense = behavioral thermoregulation, therefore conserve water - nocturnal activity - occupy burrow - seek shade - change body posture

13. Responding to High Heat Loads 2) alter insulation - see factor affecting insulation 3) cyclic TB 4) hyperthermia: controlled elevation of TB 5) evaporative cooling - tremendous water loss

14. Endothermy & Thermoregulation Endothermic Strategies for Coping with Temperature Extremes • Heterothermy: fluctuating TB = energy conservation strategy • Hypothermia: controlled lowering of TB; approach TA daily torpor: TB lowered for only part of each day; reduces food intake demands, lowers heat loss e.g., bats & some rodents

15. daily torpor Is this modern or primitive?

16. Endothermy & Thermoregulation Endothermic Strategies for Coping with Temperature Extremes • Hypothermia: estivation: summer sleep; common in small, desert mammals; conserves energy & water hibernation: seasonal lowering of TB in relation to cold temperaturs and/or low food availability

17. Endothermy & Thermoregulation Endothermic Strategies for Coping with Temperature Extremes • Hypothermia *shallow hibernation – periods of sleep with moderate TB reduction (raccoon, skunk, badger, bear) *deep hibernation – TB drops within 2-3oC of TA; sleep bouts (entry, deep sleep, arousal) (various bats, ground squirrels, woodchuck/marmot

18. Endothermy & Thermoregulation Thermoregulation in Bats *large body size = homeothermic *small body size = many heterothermic • Many with circadian activity cycles, lower TB 2-3oC at day • Daily torpor & hibernation • Relative to low temps & high energy expended for flight • Patagial membranes

19. Excretion &Water Balance Vertebrate kidney = filtration-reabsorption system - excrete waste as hypertonic urine relative to blood (because of Loop of Henle) - longer Loop of Henle = more concentrated urine

22. Passive, Countercurrent Multiplying Model of mammalian kidney • Passive refers to diffusion of NaCl out of ascending limb of Loop of Henle (LOH) • Countercurrent refers to opposite direction of flow of filtrate in descending & ascending limbs of LOH • Multiplier refers to increase [NaCl] in inner medulla of kidney relative to outer medulla

23. Endocrine Control & ADH (vasopressin)

24. antidiuretic hormone (ADH) - produced by hypothalamus & released by posterior pituitary; key hormone regulating kidney function ADH & Dehydration • ADH increases permeability of end of distal tubule & collecting duct of LOH • Increases multiplier effect • Concentrates urine; much of remaining H2O removed

25. ADH & Hydration • ADH production decreased; not released • Distal tubule & collecting duct permeability lowered • Multiplier effect decreases • [urine] decreases; extra H2O leaves body

26. Rodents – Arid vs. Mesic Habitats • Rodents in arid habitats have larger pituitary stores of ADH per unit body weight compared to rodents in mesic habitats • In general, water regulation is relatively simple in mammals from mesic habitats (e.g., high availability of drinking water, wet food, “low” water loss via evaporation) • Mammals in arid habitats must contend with stresses on their water balance & must maintain efficient water regulation systems

27. Excretion &Water Balance Rodents – Arid vs. Mesic Habitats General Sources of Water: - moist foods - metabolic water - drinking water General Ways of Losing Water: - evaporation - urination - defecation - lactation

28. Excretion &Water Balance Strategies for Water Regulation in Arid Habitats: • Consume Wet Food • May not be more efficient at water regulation • Must consume large quantities of food with high moisture content (e.g., succulent plants, insects…) • Many must counter toxins and/or salts in food material, e.g., oxalic acids in succulents or salts in halophylic plants

29. Excretion &Water Balance Strategies for Water Regulation in Arid Habitats: • Consume Wet Food • Also may exhibit behavioral mechanisms to reduce water loss, e.g., burrowing and/or foraging at night thereby balancing evaporative water loss : food water gain • Variable concentration of urine & feces

30. Excretion &Water Balance Strategies for Water Regulation in Arid Habitats: 2) Thermoregulation Mechanisms • Hyperthermia = reduce evaporation • Fewer sweat glands; panting rather than sweating • Reduce respiratory rate

31. Excretion &Water Balance Strategies for Water Regulation in Arid Habitats: 3) Periodic trips to Water Holes/Rivers (if available) • Mammals not independent of drinking water • Must obtain water every 1-2+ days (variations on periodicity of water requirements) • Variable concentration of urine & feces

32. Excretion &Water Balance Strategies for Water Regulation in Arid Habitats: 3) Periodic trips to Water Holes/Rivers (if available) e.g., camels • Hyperthermia (7o shifts) • Concentrate urine & feces • Tolerate extensive water loss over long periods (25% bw) • Maintain fluid blood • Exhale cooled & dehydrated air • Replace lost water quickly; consume large amounts of water when available

33. Excretion &Water Balance Strategies for Water Regulation in Arid Habitats: 4) “Water Independence” • Many kangaroo rates = excellent examples • Low availability of drinking water and/or moist foods; therefore do not rely on these sources • Rely on water formed via cellular respiration (metabolic water) Glucose + O2 CO2 + ATP + H2O

34. Excretion &Water Balance Strategies for Water Regulation in Arid Habitats: 4) “Water Independence” • Diet mainly seeds = high in carbohydrates = can extract high concentrations of water via catabolism, e.g., 2 g of food = 1 g of metabolic water • “super” concentration of urine via extremely long LOH relative to body size & dry feces (water reabsorption in small & large intestines and less water allocated) • No sweating

35. Most water loss via respiration Strategies to Reduce Water Loss via Respiration: (“Water-Independent” Mammals) 1) Heat exchange systems • Exhale air cooler than TB results in condensation of water before air leaves nasal passage (regional heterothermy = nasal passages) • Forage at night (respiratory water loss lowest) • Increase metabolism in accordance with low night TA thereby increasing metabolic water production & need to obtain more seeds

36. Excretion &Water Balance Strategies to Reduce Water Loss via Respiration: (“Water-Independent” Mammals) 3) Rest in burrow during day & plug entrance with soil • Lower TA & higher humidity in burrow relative to above ground, therefore lower respiratory water loss

37. Excretion &Water Balance Lactation & Water Balance: • Tremendous seasonal loss of water for females • Must recycle as much water as possible (behavioral adaptation) and/or drink frequently (maintain den, nest, etc… relatively close to dependable water source, e.g., wolf dens) • Recycle water via ingestion of urine & feces from young, thus retrieving some of water lost via lactation (common in “water-independent” mammals and those with altricial young