Osmoregulation = keeping water and
salt balanced in the body
• Question 1: why is this important
– Come up with three reasons
• Question 2: What water and salt problems
do the following organisms face?
– Freshwater fish
– Marine fish
– Marine birds
– Marine mammals
• Question 3: How might each group solve
those problems?
Definitions
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Solute
Solvent
Osmosis
Osmotic Pressure
Osmolarity
Hyperosmotic
Hypoosmotic
Osmoconformer
Osmoregulator
Solutes are dissolved particles in
solution (any type)
•Osmotic pressure: the pressure of water to enter, given
the solute concentration
•--depends on the number of solutes/unit volume (rather
than chemical nature of solutes)
•Osmotic pressure: the pressure of water
to enter, given the solute concentration
isosmotic
(osmotic pressure is equal)
•Osmotic pressure: the pressure of water
to enter, given the solute concentration
hypersmotic
(higher osmotic pressure)
hyposmotic
(lower osmotic pressure)
Water always moves from an area of low osmotic
pressure to an area of high osmotic pressure
osmotic pressure: the pressure of
water to enter, given the solute
concentration
Osmosis: movement of water from an
Area with lower osmotic pressure to
Higher osmotic pressure
Hyperosmotic (higher
osmotic pressure)
Hyposmotic (lower
osmotic pressure)
Osmotic pressures are generally
described in osmolar units:
Osmolarity
= concentration of solutes in a solution
Osmolarity vs. Molarity:
150 mMol sucrose = 150 mOsm sucrose
150 mMol NaCl
= 300 mOsm NaCl
Definitions
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Solute: Dissolved particles in a solution
Solvent: What the particles are dissolved in
movement of water from an area with lower
Osmosis: osmotic pressure to higher osmotic pressure
Osmotic Pressure: the pressure of water to enter, given
the solute concentration
Osmolarity: Concentration of solutes in a solution
Hyperosmotic: Higher osmotic pressure
Hypoosmotic: Lower osmotic pressure
Osmoconformer: Body fluid isoosmotic with envir.
fluid osmolarity regulated
Osmoregulator: Body
in opposition to environment
Freshwater teleosts: Osmoregulators
Hyperosmotic to environment
Problems?
• water gain
• salt loss
Solutions?
• Lots of dilute urine
• move salt into blood
The gills have specialized cells:
*
CHLORIDE CELLS: they result in the
active uptake of ions across the gills
Amphibians: osmoregulators
Hyperosmotic to environment
Main osmoregulatory
organ = skin
Solutions?
Problems?
• Gaining water
• Losing salt
• dilute urine
• pump salt into body
…but no gills, so no chloride cells…
Active transport of salts via skin:
3 Na+
ClCl-
Cl-
2 K+
ATP
• Active transport of Na+ into animal
• Cl- follows passively (electric gradient)
Marine Strategies
osmoconformers
ionoconformer
ionoregulator
Cl-
Na+
Cartilaginous fish
osmoregulator
Marine teleosts: Osmoregulators
(hyposmotic to environment)
Problems?
• water loss
•
salt gain
Solutions?
• gain water (food, drink)
• produce little urine
(isosmotic to plasma)
• excrete salt …
How?
Chloride Cells in the gills!
Actively pump ions OUT
Marine reptiles and birds…
Osmoregulators
Blood is hyposmotic to seawater
Can’t concentrate urine
Can concentrate urine (a
*little* bit!)
Marine reptiles and birds…
How do
they get
rid of huge
salt load?
Salt glands!
seawater
Nasal fluid
urine
3% salt
5 % salt
0.3% salt
Salt glands
Na+ mOsm
seawater
470
sea snake
620
sea turtle
690
Marine Iguana
1000-1400
gull
600-900
cormorant
500-600
petrel
900-1100
• salt is excreted from the gland to outside the body
• more concentrated than sea water!
• mechanism is same in marine reptiles
-but salt gland is in different places
Marine Mammals
Live in seawater…but no chloride cells, no salt glands…?
The Mammalian Kidney
How do mammals make
concentrated urine?
Each nephron has a
loop of Henle:
nephron
loop
of
Henle
mammalian nephron:
Loop of Henle
• Na+ is pumped
out of the filtrate
300 mOsm
•Results in osmotic
gradient in the
kidney ECF
600
•Why does this
900
matter?
Na+
Na+
1200 mOsm
300
Na+
Na+600
Na+900
Na+
1200
Cortex
Outer
Medulla
Inner
Medulla
As filtrate passes through the
collecting duct, it loses water
to the ECF
How concentrated can the
filtrate become in this
organism?
As concentrated as the ECF
300
Loop of Henle
~150
300
H2O
600
600
H2O
H2O
900
900
H2O
1200
mOsm
1200
mOsm
Cortex
Outer
Medulla
Inner
Medulla
Final urine is hyperosmotic
to plasma
• up to 4X in regular terrestrial mammals
• up to 6X in marine mammals
• up to 30X in desert mammals!
Marine Mammals
Live in seawater…but
no chloride cells, no salt glands…?
Several
Adaptations:
1. Long loop of henle in the kidney
--concentrated urine
--less water lost with waste
2. Diet
--carnivores, eating mostly
vertebrates
--vertebrates have lower osmolarity
3. Absence of sweat glands
Osmoregulation = aquatic animals
• Question 1: why is this important
– Low solute concentration: cells shrink
– High solute concentration: cells burst
– Cells need proper ion balance to function
• Muscle, nerve cells; Na+/K+ pump
• Question 2: Problems?
• Question 3: solutions?
– Problem: solution
– Freshwater fish
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Water gain: produce lots of dilute urine
Salt loss: pump salt in through chloride cells in gills
– Marine fish
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Osmoconformers: no regulation
ionoconformers: increase plasma solutes—Urea
Osmoregulators
– Lose water: drink lots of sea water, produce little urine
– Gain salt: Chloride Cells in gills
– Marine birds
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Gain salt: excrete salt in salt glands
– Marine mammals
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Gain salt: excrete hi solute urine
TERRESTRIAL VERTEBRATES
Total Water gain and loss:
2.2 + 0.3 = 1.6 + 0.9
In humans:
Water Gain:
Water Loss:
1. Food/water intake
1. Excretion
a) Fecal
b) Urinary
+ 2.2 L/day
2. Metabolic water
+ 0.3 L/day
- 1.6 L/day
2. Evaporative Water
Loss
a) Cutaneous
b) Respiratory
- 0.9 L/day
3. Reproduction
Nitrogenous Wastes affect Water
Balance
Proteins
Nucleic acids
Nitrogenous waste products
AMMONIA
• Water soluble
• Very toxic
• Excreted w/lots
of water
UREA
• Water soluble
• Low toxicity
• Excreted
w/less water
URIC ACID
• Not water soluble
• Low toxicity
• Excreted
w/little
water
Excretion
Tortoises and Turtles:
% of urinary nitrogen
Species
Habitat
Ammonia
Urea
Uric Acid
Red-eared slider
Freshwater
79
17
4
Forest hinge-back
tortoise
Moist Terrestrial
6
61
4
Mediterranean spurthighed tortoise
Dry terrestrial
4
22
52
Texas tortoise
Desert
4
3
93
• ammonia
Teleost fish
Amphibians reptiles
• urea
chondrichthyes
Teleost fish Amphibians reptiles
• uric acid
Amphibians
Birds and reptiles
mammals
Mammals:
• most drink, eat foods high in water
•very concentrated urine
BUT, what about desert mammals?
How do Kangaroo Rats Cope?
How?
Metabolic water:
C6H12O6 + 6O2
1 g glucose
• don’t pant
• few sweat glands
• LONG loop of henle
•Human urine= 1200 mOsm
•Kangaroo rat = 5500 mOsm
• eat dry food *
• don’t drink!
• don’t tolerate dehydration!
6 CO2 + 6H2O
0.6 g water
35 g
Water gains:
100g barley
=
54 mL: oxidation water
6 mL: absorbed water
60 mL water
=
Water losses:
16.1 mL: urine, feces
43.9 mL: evaporation
60 mL water
Urine = 9x higher osmolarity than sea water!!
Terrestrial summary
• Water in:
– Food and drink
– Metabolic water
• Water out:
– excretion
– Evaporative water loss
• Adaptations in the desert?
– Extended loop of henle
– Reduced evaporative water loss
• (gain in camel nose)
– High dehydration tolerance