Transcript Excretion &Water Balance

Endothermy &
Thermoregulation
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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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Modes of Increasing Heat Production
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below thermoneutrality (thermogenic
processes)
2) Nonshivering thermogenesis (NST):
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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
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Modes of Increasing Heat Production
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below thermoneutrality (thermogenic
processes)
2) Nonshivering thermogenesis (NST):
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best site = brown adipose tissue or brown
fat
brown fat has: large # mitochondria
large # blood vessels
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Modes of Increasing Heat Production
– below thermoneutrality (thermogenic processes)
2) Nonshivering thermogenesis (NST):
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brown fat = hibernating gland (misnomer)
brown fat prominent in:
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cold-acclimated or winter-acclimated adults, especially small to
medium body size
hibernators
neonates
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Modes of Increasing Heat Production
–
below thermoneutrality (thermogenic processes)
3) Activity
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increase heat production in large but not most small
mammals
shivering (not NST) is inhibited by activity
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Modes of Increasing Heat Production
–
below thermoneutrality (thermogenic processes)
4) Regional Heterothermy – common to all mammals
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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
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
5) evaporative cooling
- tremendous water loss
of TB
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 torpor
Is 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
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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
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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
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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 Balance
Strategies for Water Regulation in Arid
Habitats:
3) Periodic trips to Water Holes/Rivers
(if available)
e.g., camels
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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 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 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
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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: (“WaterIndependent” 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 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