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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.

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endothermy thermoregulation
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 thermoregulation1
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 thermoregulation2
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

slide4
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
slide5
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
slide6
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)
slide7
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

slide8
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

slide9
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

slide11
Regional

Heterothermy

& Performance

slide12
Responding to High Heat Loads

1) first defense = behavioral thermoregulation, therefore conserve water

- nocturnal activity

- occupy burrow

- seek shade

- change body posture

slide13
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 thermoregulation3
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

slide15
daily torpor

Is this modern or primitive?

endothermy thermoregulation4
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

endothermy thermoregulation5
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

endothermy thermoregulation6
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
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

slide22
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
slide23

Endocrine Control

&

ADH (vasopressin)

slide24
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
slide25
ADH & Hydration
  • ADH production decreased; not released
  • Distal tubule & collecting duct permeability lowered
  • Multiplier effect decreases
  • [urine] decreases; extra H2O leaves body
slide26
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 balance1
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 balance2
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
excretion water balance3
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
excretion water balance4
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 balance5
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 balance6
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
excretion water balance7
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

excretion water balance8
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
slide35
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
excretion water balance9
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 balance10
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
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