Water & Salt Physiology

• Hyposmotic (U/P<1) urine less concentrated than blood (freshwater & most terrestrial animals) • Isosmotic (U/P = 1) urine is the same concentration as the blood • Hyperosmotic (U/P>1) = urine more concentrated than blood (mammals, birds & insects)

Ratio of urine composition (U) over plasma (P) composition –> Urine composition (150 mOsm) / plasma composition (300 mOsm)

• Uniform and stable • Salinity = 3.36 g kg • Osmotic pressure = 1000 mOsm

• Salinity < 0.5 g kg • Uniform osmotic pressure = 0.5 - 0.15 mOsm • Variations in ion concentrations from one body of freshwater to another (High Ca2+ = hard water Low Ca2+ = soft water)

• Highly variable in time and space • Intermediate salinity = 0.5 - 30 g kg • Osmotic pressure = 15 - 850 mOsm

• Water in gaseous state and free of salts • Water vapor pressure • Limit to water vapor pressure = saturation • Point of saturation increases with temperature • Warmer air contains more water vapor • Evaporation increases in drier env. • Water loss from evaporation is the biggest challenge for terrestrial env.

• Water gain to try & dilute their blood • Salt water loss = ions move down concentration gradient (Hyperosmotic - more concentrated than their environment)

• Osmotic and ionic gradients • Permeability of animals outer body to water and ions • Surface area across which exchange is occurring

• Produce dilute urine in large volume • Hyposmotic to the blood = U/P osmotic and ionic ratios <1 • Kidneys are regulatory = regulations all the time

Actively uptake Na+ and Cl- into blood

• Water loss = water wants to move out to dilute sea water • Salt gain = ions move in down concentration gradient (Hyposmotic = less concentrated than their env.)

Drink seawater and replace water lost by osmosis - Salt balance is disrupted - Excrete Mg2+ and SO2-4 (divalent ions) in urine at kidneys - Actively uses ATP

Actively excrete Na+ and Cl- (monovalent ions) Actively uses ATP

Capable of living in dry, water-poor environments - lipid layer to reduce water loss - respiratory surfaces inside body

Restricted to humid, water-rich environments - live underground, leaf litter, under logs/rocks - can only reduce water loss by living in a humid environment - high permeability (skin, exoskeleton)

Evaporation from breathing - air is saturated when exhaled, but exhaled at a lower temperature

• Air inhaled = warm air + add water • Air exhaled = cool air + remove water • Mammals lose more water when in a warmer environment

Water loss in urine production - concentrate urine to retain water - make poorly soluble or insoluble nitrogenous wastes so don’t need as much water (Desert animals)

• Humidic - high evaporative water loss • Isosmotic urine (Do not drink) • Use bladder for water storage , NaCl actively transported

Eat primarily insects + plants - High water content - Low metabolic rate - Low respiratory evaporative water loss - Nitrogenous waste = uric acid or urate salts - Behavioral adaptations (shade + sun)

Eat insects + plants - Higher metabolic rate - Higher respiratory evaporative water loss

Thorny devil sucks water up in skin grooves

Modulate core body temperature - reduce water use for thermoregulation - get water from food so can live for months or years w/o drinking