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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
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
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
• 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
• 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
• 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)
• 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
• 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
• 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
rete mirabile
RegionalHeterothermy
& Performance
Responding to High Heat Loads
1) first defense = behavioral thermoregulation, therefore conserve water
- nocturnal activity
- occupy burrow
- seek shade
- change body posture
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
Endothermy & Thermoregulation
Endothermic Strategies for Coping with Temperature Extremes
• Heterothermy: fluctuating TB
= energy conservation strategy
1) 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
daily torporIs this modern or primitive?
Endothermy & Thermoregulation
Endothermic Strategies for Coping with Temperature Extremes
1) 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
Endothermy & Thermoregulation
Endothermic Strategies for Coping with Temperature Extremes
1) 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
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
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
Passive, Countercurrent Multiplying Model of mammalian kidney
1) Passive refers to diffusion of NaCl out of ascending limb of Loop of Henle (LOH)
2) Countercurrent refers to opposite direction of flow of filtrate in descending & ascending limbs of LOH
3) Multiplier refers to increase [NaCl] in inner medulla of kidney relative to outer medulla
Endocrine Control&
ADH (vasopressin)
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
ADH & Hydration
• ADH production decreased; not released
• Distal tubule & collecting duct permeability lowered
• Multiplier effect decreases
• [urine] decreases; extra H2O leaves body
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
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
Excretion &Water Balance
Strategies for Water Regulation in Arid Habitats:
1) 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
Excretion &Water Balance
Strategies for Water Regulation in Arid Habitats:
1) 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
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
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
Excretion &Water BalanceStrategies 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
Excretion &Water BalanceStrategies 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
Excretion &Water BalanceStrategies 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
• 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)
2) 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
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
Excretion &Water BalanceLactation & 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