Mammals

Mammals

Water Gain
1. Drinking
  1. Unreliable source
    1. Rainfall unpredictable
      1. Arid = 6 - 10mm, Semi-arid = 50mm +
      2. Flashfloods
  2. Specialist actions to reduce dehydration
    1. Camel
2. Environment
  1. absorption of moisture in dens or burrows = condensation on cool walls
3. Diet
  1. Omnivores can obtain 70% of water from insects
Water Loss
1. REWL (Respiratory evaporative water loss)
  1. Nasal Counter-current exchange
    1. Affected by the surface area
  2. 100% saturated air
    1. Delicate structures of the lungs must be damp
    2. Camels do not breath out 100% saturated air
2. TEWL (Transepidermal evaporative water loss)
  1. Mammalian skin permeable and allows water to pass through
Stratergies for reducing water loss
1. Concentratation of Nitrogenous waste
  1. Faeces
    1. Can dehydrate faeces - depending on species
  2. Urine
    1. Effective kidney function
      1. Loop of Henle (Counter current multiplyer system)
      2. Can respond to dehydration by concentrating urine
    2. Hyperosmotic to plasma
    3. Ureotylic - production of urea = less water intensive than uric acid, but slightly more toxic
Large Mammals = Endurer
1. Camel
  1. Can rehydrate 200 liters in 3 minutes
    1. Stores water in the gut to avoid blood dilution
  2. Enhanced nasal counter-current exchange
  3. Heterothermic - when depreived of water can slowly increase body tempr from 35 - 41 C during the day and lose heat during the night
  4. Does not require EWL to reduce body temperature (saves 5 liters of water a day)
  5. Can store urea in tissue when dehydrated
2. Sand Gazelle
  1. Heart and liver shrinks during times of starvation or dehydration
    1. Smaller hearts = lower metabolism = reduction in water by 1/3
    2. Ostrowski et al, 2006
3. Lower metabolism = lose heat slower = lowered EWL
4. Kangaroo
  1. High urine concentration - 3700mOsmol
  2. Lowered rates of metabolism and a lowered body temperature
    1. Reduction in REWL
  3. Circadian locomotory rhythm = many are nocturnal
  4. Lie in cool soil to reduce body temperature in hot days
    1. Vasodilation = lick forarms to cool blood down
  5. Red Kangaroo VS Grey Eastern Kangaroo
Small Mammals = Evader
1. Kangaroo Rat
  1. Eat a carb rich diet and still stayes hydrated by obtaining water from seeds
    1. Knut Schmidt-Nielson (1951)
      1. Fur lined cheek pouches
  2. Dry faeces reduces nitrogenous water loss
  3. 90% of water gained by metabolism, 10% absorbed by dry food
  4. 25% of water lost by urine, 5% lost by faeces, 70% lost by EWL
2. Higher metabolism = lose heat quicker = higher EWL

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	Created by Adam Heywood over 6 years ago