water and solute balance 2

Water and Solute Balance 2Water and Solute Balance 2

Ionic and Osmotic Regulation in Different Ionic and Osmotic Regulation in Different Organisms in Different EnvironmentsOrganisms in Different Environments

OutlineLast time:

Ionic and osmotic regulation in and out of the cell

Ion uptake mechanisms

This Time:

(1) Ionic Regulation and Excretion

(3) Ionic and Osmotic Regulation in Different Organisms in Different Environments


Ion Uptake vs Ion ExcretionIon Uptake vs Ion Excretion

Ion Uptake

The Ion Uptake enzymes are often conserved in amino acid sequence ( often no structural differences)

The following are often NOT conserved: Distribution and concentration of Ion Uptake

enzymes in a cell

The organization of the cells in an organ

Ion UptakeIon Uptake vs Ion ExcretionIon Excretion

How can ionic regulation be accomplished through these methods?

And can the same organs be involved?

UrineUrine

What is it?

Varies

Amino (-NH2) groups unused from catabolism

Salts and Water

Osmotic concentration depends on Environment

Osmoregulated urine is a convenient way to regulate ionic concentration (through excretion) and remove nitrogenous wastes

UrineUrine concentrations relative to bloodblood

Marine invertebratesMarine invertebrates isosmoticisosmotic

Freshwater inverts + vertsFreshwater inverts + verts hyposmotic (dilute)hyposmotic (dilute)

Terrestrial AnimalsTerrestrial Animals hyperosmotichyperosmotic

Marine Verts Marine Verts

teleoststeleosts isosmotic isosmotic (use gills to remove salt)(use gills to remove salt)

elasmobranchselasmobranchs close to isosmoticclose to isosmotic mammalsmammals hyperosmotichyperosmotic

Costs and Benefits of different nitrogenous waste products (Table 5.7)

Ammonia: Marine Animals, Inexpensive, water soluble, 1N/molec.(lose less C), permeable thru lipid bilayer, highly toxic

Urea: Expensive (2 ATP), water soluble, 2N/molec., moderately permeable thru lipid bilayer, moderately toxic

Uric Acid: Very Expensive, water insoluble, minimize water loss, not permeable thru lipid bilayer, 4N/molec., Low toxicity


Osmo/Ion-regulatory OrgansOsmo/Ion-regulatory Organs

Question:

What do What do osmoregulatoryosmoregulatory organs of different organs of different animals have in common?animals have in common?

In what ways do they differ and why?In what ways do they differ and why?

What are some key differences between What are some key differences between osmoregulationosmoregulation in aquatic and terrestrial in aquatic and terrestrial environments?environments?

Most animals have tubular osmoregulatory structures involving the same types of ion uptake and excretion mechanisms (see book)

In aquatic habitats nitrogenous excretion can occur across gills or integument (skin)…will be removed through simple diffusion

In terrestrial habitat osmoregulation and (nitrogenous) excretion is done together…use excess water to remove wastes

Osmoregulatory Organs

Contractile vacuoles Protozoans, Sponges

None demonstrated Coelenterates (strictly marine) Echinoderms (strictly marine)

Nephridial organs Protonephridia (closed ends) Platyhelminthes, Aschelminthes Metanephridia (open ends) Annelids Nephridia Molluscs

Gut Many animalsAntennal glands CrustaceansMalpighian tubules InsectsKidneys VertebratesGills Crustaceans, Molluscs, FishesSkin AmphibiansSalt glands Birds, Reptiles

Common Themes

Tubular structures

Remove or absorb ions

Remove or take up water

Protonephridia of flatworms

Metanephridia of Annelids (segmented worms)

Fish Gills

V-H+-ATPase Na+,K+-ATPase

Salt glands of birds

Vertebrate Kidney

Contains simple tubular structures

But which are compacted Around 1 million of these tubules (nephrons)

in humans

Filtration-Reabsorption System

Evolutionary History of the kidney

First evolved in freshwater teleosts

Freshwater fish are hyperosmotic relative to environment

Face two problems: (1) Water rushing in thru osmosis

(2) loss of solutes

Solution: (1) Active uptake in gills

(2) Kidney to excrete dilute urine (hypotonic)

(3) Reabsorb ions across nephron tubules

Vertebrate Kidney

Enormous osmo-iono-regulatory capacity Receives 20-25% of total cardiac output

Osmoregulation Excretion Regulate Blood Pressure pH Balance: produces about 1 liter of slightly acidic

urine daily (pH 6.0)

(blood maintained at pH 7.4)

Human Kidney

Figure 5.16The Functional Unit

The Nephron

Mammalian Kidney

Countercurrent Multiplier system

Na+ Cl- are pumped out

3Na+


Flow moving in opposite directions Flow moving in opposite directions (countercurrent)(countercurrent)

Where the concentration difference is not big Where the concentration difference is not big between the descending and ascending side of the between the descending and ascending side of the loop, BUT, along the whole length of the loop, the loop, BUT, along the whole length of the loop, the difference is additive and big (multiplicative)difference is additive and big (multiplicative)


A mechanism through which water is moved out of the tubule (to conserve water in the organism)

Na+

Cl-


A general method for exchange (heat, gas, liquid)A general method for exchange (heat, gas, liquid) (in this case water and ions)(in this case water and ions)

Creates a concentration gradient along the loopCreates a concentration gradient along the loop

Requires a loop structure Requires a loop structure

Common in animals, engineering, gills, lungsCommon in animals, engineering, gills, lungs

Relies on asymmetry and flow through the tubeRelies on asymmetry and flow through the tube


Na+ Cl- are pumped outAnd diffuses to the

Other side


Impermeable to waterImpermeable

to solutes

The interstitium becomeconcentrated


Impermeable to waterImpermeable to solutes

Water diffuses out ofThe descending loop

H20


Impermeable to waterImpermeable

to solutes

The fluid at the hairpinBecomes more concentrated

H20


Impermeable to solutes


Which gives the ascending loop

more ions to pump out


Impermeable to solutes





H20



Which causesMore water to

Diffuse out


H20 So with little energy,the fluid becomesIncreasingly concentrated


Ionic and Osmotic Regulation in Different Ionic and Osmotic Regulation in Different Organisms in Different EnvironmentsOrganisms in Different Environments

(3) Ionic and Osmotic Regulation in Different Organisms in Different Environments

Last Time: Inside Cell vs Outside Cell

This Time: Inside the Organism (both

intracellular & extracellular fluids) vs The Environment

K+

Na+

Cl-

HCO3-

Na+

K+

Mg++

Mg++

Ca++Ca++

Cl-

OrganicAnions

Extracellular Fluids Extracellular Fluids (blood)(blood)

The Cell

Last time we discussed strategies for regulation concentrations in and out of the cell

K+

Na+

Mg++

Ca++

Cl-

OrganicAnions

The Cell

Cl-HCO3-

Na+

K+

Mg++

Ca++

Extracellular FluidsExtracellular Fluids

The EnvironmentThe EnvironmentNow, we want to discuss the interaction between the organism and the Environment

Osmo/Iono-conformers: Osmotic pressure Osmo/Iono-conformers: Osmotic pressure (or ionic concentration) of extracellular fluid (or ionic concentration) of extracellular fluid (blood) matches that of the environment (blood) matches that of the environment

Osmo/Iono-regulators: Maintain relatively Osmo/Iono-regulators: Maintain relatively stable blood osmotic pressure (ionic stable blood osmotic pressure (ionic concentration) over a range of pressures concentration) over a range of pressures (ionic concentrations) in the environment(ionic concentrations) in the environment

Hyperregulation

Hyporegulation

Daphnia from Lake Mendota

Which is most likely to be Which is most likely to be an Osmo/Iono-conformer?an Osmo/Iono-conformer?

Differences in Body Fluid Regulation in Different Environments

Evolutionary patterns

Intracellular ionic concentrations are conserved (constraints of basic cell biochemistry)

Extracellular fluids and intra and extra cellular osmotic regulation varies much more

Osmotic Concentration (mOsm) Ionic Concentration (mM)

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Urea

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Teleost(Salmon)

TerrestrialVertebrate(Human)

FreshwaterInvertebrate

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Intracellular differences among species

Ionic composition is more conserved across species (differences related to evolutionary adaptations)

Osmotic concentration differs among species: Using osmolytes or urea to fill Solute Gap with Environment Depends on environment And on Evolutionary History


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Relativelyconserved

Osmotic differences among species

Ionic composition is more conserved across species

Osmotic concentration differs greatly among species: Need to maintain osmotic constancy in and out of the cell, and then try to

approach the osmotic concentration of the environment Using osmolytes or urea to fill Solute Gap with Environment Depends on Environment: Extracellular fluids provide a Buffer between the

cells and the Environment And on Evolutionary History


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OsmoticConcentrations vary

Osmolytes Organic osmolytes: small solutes used by cells

to maintain cell volume

Compatible solutes: does not perturb macromolecules in the cell and are interchangeable (one functions as well as another)

However, not all osmolytes are compatible solutes and some have specific functions (read about in Yancey 2005)

Osmotic RegulationExamples of Osmolytes: Carbohydrates, such as

trehalose, sucrose,

and polyhydric alcohols, such as glycerol and mannitol

Free amino acids and their derivatives, including glycine, proline, taurine, and beta-alanine

Urea and methyl amines such as trimethyl amine oxide (TMAO) and betaine

Patterns of osmolyte composition in intracellular fluids

Yancey 2005


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Extracellular Ionic & osmotic

concentrations vary among species in different habitats


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Match environment

Unusually low

Deal with low salinity

No longer an osmotic issue

Metabolic Cost of Osmoregulation

The cost of iono- and osmoregulation varies greatly among animals

Depends on gradient between environment and Extracellular fluid

Permeability of the integument (skin) And particular evolutionary strategy

Examples:Low in Marine InvertebratesMarine Teleosts: 8-17% of resting metabolic rateFreshwater teleosts: 3-7% of resting metabolic rate


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Marine Invertebrates Extracellular ionic & osmotic concentrations close to sea water Some species do not regulate at all

Intracellular ionic concentration conserved (low) Intracellular osmotic concentration high

(Osmotic solute gap filled by osmolytes) High body permeability to water and ions

Isosmotic urine

Extracellular ionic composition is close to seawater(intracellular is not)

Adaptations to Fresh Water


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Freshwater species are hyperosmotic relative to the environment

Energetic cost of osmotic-ionic regulation is 3-7% of resting metabolic rate

(1) Reduce ionic and osmotic gradient with the environment to reduce energetic cost

(2) Reduce body permeability to ions

(3) Excrete high volumes of dilute urine(4) Active Ion uptake

(5) Obtain ions from food

Freshwater animals have reduced ionic and osmotic body fluid concentrations

Fresh

Marine

Composition of blood plasma and other fluids

Freshwater animals excrete high volumes of dilute urine

Very dilute

Did they evolve in Fresh Water?

VertebratesVertebrates

Low Extracellular ionic AND osmotic concentration They are osmoregulators, even when they return to marine

habitats.

Bones form more readily in Fresh Water (relative large availability of Calcium)

Greater degree of regulation


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Elasmobranchs, cartilaginous fishes

Low Extracellular ionic concentration!!!

(1/3 of seawater, evolution in fresh water?)

Solute gap for BOTH extra and intracellular fluids filled by ureaurea!!!

Some species slightly hyperosmotic

(limited osmoregulator, not osmoconformer)


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Elasmobranchs, cartilaginous fishes

Withers PC. 1998. Urea: diverse functions of a 'waste' product.Clin Exp Pharmacol Physiol. 25:722-7.

Urea is a waste product It destabilized proteins (but Trimethylamine N-oxide

TMAO stabilizes)

Close to isosmotic Don’t need to drink

Some are slightly hyperosmotic Water flows into gills (gains the water it needs this way)


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Extracellular fluid (blood) concentration 1/4 of marine animal More concentrated than freshwater animal

Not have to worry about loss of ions through osmosis

(so osmotic conc. can be higher than in fresh water) Instead, problem of evaporation (water loss through respiration) Mammals: another issue is water used for thermoregulation (sweat)

Terrestrial Vertebrates

Terrestrial

Adaptations

Active behavioral uptake of water

Ion uptake from food

Skin and cuticle evolved to prevent water loss

Concentrated Urine (kidneys)

Some terrestrial animals can survive water loss (camel- survive 30% loss)

Essentially a terrestrial vertebrate (cow) living in the seaExcrete Concentrated Urine (powerful kidneys)

water and solute balance 2

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