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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


  • 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



Regional

Heterothermy

& 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 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


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


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


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 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


  • 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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