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• 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)

isosmotic

•Osmotic pressure: the pressure of water to enter, given the solute concentration

(osmotic pressure is equal)

hypersmotic(higher osmotic pressure)

hyposmotic(lower osmotic pressure)

•Osmotic pressure: the pressure of water to enter, given the solute concentration

Water always moves from an area of low osmotic pressure to an area of high osmotic pressure

Hyposmotic (lower osmotic pressure)

Hyperosmotic (higher osmotic pressure)

osmotic pressure: the pressure of water to enter, given the solute concentration

Osmosis: movement of water from anArea with lower osmotic pressure to Higher osmotic pressure

Osmolarity= concentration of solutes in a solution

Osmolarity vs. Molarity:

150 mMol sucrose= 150 mOsm sucrose

150 mMol NaCl = 300 mOsm NaCl

Osmotic pressures are generally described in osmolar units:

Definitions• Solute:• Solvent:• Osmosis:• Osmotic Pressure:• Osmolarity:• Hyperosmotic:• Hypoosmotic:• Osmoconformer:• Osmoregulator:

Dissolved particles in a solution

movement of water from an area with lower osmotic pressure to higher osmotic pressure the pressure of water to enter,

given the solute concentration

Concentration of solutes in a solution

Higher osmotic pressure

Lower osmotic pressure

What the particles are dissolved in

Body fluid isoosmotic with envir.

Body fluid osmolarity regulated in opposition to environment

Freshwater teleosts: Osmoregulators

Problems?

• water gain• salt loss

Solutions?

• move salt into blood

• Lots of dilute urine

* The gills have specialized cells:

CHLORIDE CELLS: they result in the active uptake of ions across the gills

Hyperosmotic to environment

Main osmoregulatory

organ = skin

Problems?• Gaining water

Solutions?

• Losing salt

• dilute urine• pump salt into body

Amphibians: osmoregulatorsHyperosmotic to environment

…but no gills, so no chloride cells…

• Active transport of Na+ into animal

2 K+

3 Na+

ATP

Active transport of salts via skin:

Cl-Cl-

Cl-

• Cl- follows passively (electric gradient)

Cl-

Na+

osmoconformersosmoregulator

ionoconformerionoregulator

Marine Strategies

Cartilaginous fish

Marine teleosts:Osmoregulators(hyposmotic to environment)

Problems?• water loss

Solutions?

How?• excrete salt …

• salt gain

• produce little urine (isosmotic to plasma)

• gain water (food, drink)

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!)

How do they get rid of huge salt load?

Marine reptiles and birds…

seawater3% salt

Salt glands!

Nasal fluid5 % salt

urine0.3% salt

Salt glands

• 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

Na+ mOsm

seawater 470

sea snake 620

sea turtle 690

Marine Iguana 1000-1400

gull 600-900

cormorant 500-600

petrel 900-1100

Marine MammalsLive 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 loopofHenle

Cortex

OuterMedulla

InnerMedulla

Loop of Henle

mammalian nephron:

Na+Na+

Na+Na+

Na+Na+

• Na+ is pumped out of the filtrate

•Results in osmotic gradient in the kidney ECF

•Why does this matter?

300

600

900

300 mOsm

600

900

1200 mOsm 1200

Cortex

OuterMedulla

InnerMedulla

Loop of HenleAs filtrate passes through the collecting duct, it loses water to the ECF

H2O

H2O

H2O

H2O

300

600

900

300

600

900

1200mOsm

1200mOsm

How concentrated can the filtrate become in this organism?

~150

As concentrated as the ECF

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 MammalsLive in seawater…but no chloride cells, no salt glands…?

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

Several Adaptations:

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

• Water gain: produce lots of dilute urine• Salt loss: pump salt in through chloride cells in gills

– Marine fish• 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• Gain salt: excrete salt in salt glands

– Marine mammals• Gain salt: excrete hi solute urine

TERRESTRIAL VERTEBRATES

Water Gain:

1. Food/water intake

2. Metabolic water

Water Loss:

1. Excretiona) Fecalb) Urinary

2. Evaporative Water Lossa) Cutaneousb) Respiratory

3. Reproduction

In humans:

+ 2.2 L/day

+ 0.3 L/day - 1.6 L/day

- 0.9 L/day

Total Water gain and loss: 2.2 + 0.3 = 1.6 + 0.9

• Water soluble• Very toxic• Excreted w/lots of water

• Not water soluble• Low toxicity• Excreted w/little water

• Water soluble• Low toxicity• Excreted w/less water

Nitrogenous Wastes affect Water Balance

Proteins Nucleic acids

Nitrogenous waste products

UREAAMMONIA URIC ACID

Excretion

• ammonia

• urea

• uric acid

Teleost fish

chondrichthyes

Birds and reptiles

mammals

Amphibians reptiles

% 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 spur-thighed tortoise

Dry terrestrial 4 22 52

Texas tortoise Desert 4 3 93

Tortoises and Turtles:

Teleost fish Amphibians

Amphibians

reptiles

Mammals:• most drink, eat foods high in water •very concentrated urine

BUT, what about desert mammals?

How do Kangaroo Rats Cope?

• 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!C6H12O6 + 6O2 6 CO2 + 6H2O

Metabolic water:

How?

1 g glucose 0.6 g water

100g barley35 g

Water gains: Water losses:

54 mL: oxidation water6 mL: absorbed water

16.1 mL: urine, feces43.9 mL: evaporation

60 mL water 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