2. 2
Key Concepts
• Water and metabolic waste
• The osmotic challenges of different
environments
• The sodium/potassium pump and ion
channels
• Nitrogenous waste
• Osmoregulation and excretion in
invertebrates
• Osmoregulation and excretion in
vertebrates
3. 3
• Osmoregulation ≠Excretion
• All organismal systems exist within a water
based environment
The cell solution is water based
Interstitial fluid is water based
Blood and hemolymph are water based
• All metabolic processes produce waste
Metabolic processes that produce nitrogen
typically produce very toxic ammonia
Water and Metabolic Waste
5. 5
Critical Thinking
• The cellular metabolism of proteins, nucleic
acids, and ATP will produce nitrogenous
waste.
6. 6
Water and Metabolic Waste
• All animals have some mechanism to
regulate water balance
• All animals have some mechanism to
regulate solute concentration
• All animals have some mechanism to
excrete nitrogenous waste products
• Osmoregulation and excretion systems vary
by habitat and phylogeny (evolutionary
history)
7. 7
Animals live in different
environments
Marine….Freshwater….Terrestrial
All animals must balance water uptake vs.
water loss and regulate solute
concentration within cells and tissues
8. 8
The osmotic challenges of different
environments – water balance
• Water regulation strategies vary by
environment
Body fluids range from 2-3 orders of magnitude
more concentrated than freshwater
Body fluids are about one order of magnitude
less concentrated than seawater for
osmoregulators
Body fluids are isotonic to seawater for
osmoconformers
Terrestrial animals face the challenge of
extreme dehydration
9. 9
The osmotic challenges of different
environments – solute balance
• All animals regulate solute content,
regardless of their water regulation strategy
• Osmoregulation always requires metabolic
energy expenditure
10. 10
The osmotic challenges of different
environments – solute balance
• In most environments, ~5% of basal
metabolic rate is used for osmoregulation
More in extreme environments
Less for osmoconformers
• Strategies involve active transport of
solutes and adaptations that adjust tissue
solute concentrations
11. 11
Water Balance in a Marine
Environment
• Marine animals that regulate water balance
are hypotonic relative to salt water (less
salty)
• Where does water go???
12. 12
Critical Thinking
• Marine animals that regulate water balance
are hypotonic relative to salt water – where
does water go???
13. 13
Critical Thinking
• Marine animals that regulate water balance
are hypotonic relative to salt water – where
does water go???
• Remember water potential!
Ψ = P - s
14. 14
Critical Thinking
• Marine animals that regulate water balance
are hypotonic relative to salt water – where
does water go???
• Water will always move from high ψ to low ψ
• Pressure is not important in this instance
(no cell wall)
• Solute concentration is much higher in the
saltwater environment than in the cytoplasm
• Water is constantly moving out of the animal
by osmosis
15. 15
Water Balance in a Marine
Environment
• Marine animals that regulate water balance
are hypotonic relative to salt water
They dehydrate and must drink lots of water
Marine bony fish excrete very little urine
• Most marine invertebrates are
osmoconformers that are isotonic to
seawater
Water balance is in dynamic equilibrium with
surrounding seawater
16. 16
Solute Balance in a Marine
Environment
• Marine osmoregulators
Gain solutes because of diffusion gradient
Excess sodium and chloride transported back to
seawater using metabolic energy, a set of linked
transport proteins, and a leaky epithelium
Kidneys filter out excess calcium, magnesium
and sulfates
• Marine osmoconformers
Actively regulate solute concentrations to
maintain homeostasis
17. 17
Figure showing how chloride cells
in fish gills regulate salts
Specialized chloride cells in the gills actively accumulate
chloride, resulting in removal of both Cl-
and Na+
18. 18
Solute Balance in a Marine
Environment
• Marine osmoregulators
Gain solutes because of diffusion gradient
Excess sodium and chloride transported back to
seawater using metabolic energy, a set of linked
transport proteins, and a leaky epithelium
Kidneys filter out excess calcium, magnesium
and sulfates
• Marine osmoconformers
Actively regulate solute concentrations to
maintain homeostasis
19. 19
Water Balance in a Freshwater
Environment
• All freshwater animals are regulators and
hypertonic relative to their environment
(more salty)
• Where does water go???
20. 20
Critical Thinking
• All freshwater animals are regulators and
hypertonic relative to freshwater – where
does water go???
21. 21
Critical Thinking
• All freshwater animals are regulators and
hypertonic relative to freshwater – where
does water go???
• Solute concentration is much lower in the
freshwater environment than in the
cytoplasm
• Water is constantly moving by osmosis into
the animal
22. 22
Water Balance in a Freshwater
Environment
• All freshwater animals are regulators
• They are constantly taking in water and
must excrete large volumes of urine
Most maintain lower cytoplasm solute
concentrations than marine regulators – helps
reduce the solute gradient and thus limits
water uptake
• Some animals can switch environments
and strategies (salmon)
23. 23
Some animals have the ability to go dormant
by extreme dehydration
http://www.youtube.com/watch?v=CKamWp610ng
The waterbear song by MalWebb