Water & Salt Physiology

Question 1

What are the urine composition and plasma composition ratios in the kidneys (U/P ratios)?

Answer 1

• 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)

Question 2

U/P ratios =

Answer 2

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

Question 3

Describe the aquatic environments ? (Open oceans)

Answer 3

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

Question 4

Describe the freshwater environments? (Lakes, rivers)

Answer 4

• 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)

Question 5

Describe the brackish water environments? (Estuaries - ocean + freshwater mixture)

Answer 5

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

Question 6

Describe the terrestrial water environments?

Answer 6

• 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.

Question 7

Describe the freshwater fish passive processes?

Answer 7

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

Question 8

What are the freshwater fish influenced by during passive processes?

Answer 8

1. Osmotic and ionic gradients
2. Permeability of animals outer body to water and ions
3. Surface area across which exchange is occurring

Question 9

How do freshwater fish regulate urine?

Answer 9

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

Question 10

What do the gills do in freshwater fish?

Answer 10

Actively uptake Na+ and Cl- into blood

Question 11

Describe the marine fish passive processes?

Answer 11

• 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.)

Question 12

How do marine fish regulate urine?

Answer 12

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

Question 13

What do the gills do in marine fish?

Answer 13

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

Question 14

Xeric =

Answer 14

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

Question 15

Humidic =

Answer 15

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)

Question 16

Respiratory evaporative water loss =

Answer 16

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

Question 17

Temporal countercurrent exchange =

Answer 17

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

Question 18

Excretory water loss =

Answer 18

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)

Question 19

Terrestrial amphibians

Answer 19

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

Question 20

Desert lizards

Answer 20

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)

Question 21

Small desert mammals

Answer 21

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

Question 22

What was an adaptation to gain water in desert lizards?

Answer 22

Thorny devil sucks water up in skin grooves

Question 23

Large desert mammals - Oryxes

Answer 23

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