Water and Solute Balance 2 Ionic and Osmotic Regulation in Different Organisms in Different Environments

Outline Last 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

Water and Solute Balance 2 Ion Uptake vs Ion Excretion

Ion Uptake n The Ion Uptake enzymes are often conserved in amino acid sequence ( often no structural differences) The following are often NOT conserved: n Distribution and concentration of Ion Uptake enzymes in a cell n The organization of the cells in an organ

Ion Uptake Ion Excretion Ion Uptake vs Ion Excretion How can ionic regulation be accomplished through these methods? And can the same organs be involved?

Urine What is it?

Varies Amino (-NH 2 ) 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

Urineblood Urine concentrations relative to blood Marine invertebrates isosmotic Freshwater inverts + verts hyposmotic (dilute) Terrestrial Animals hyperosmotic Marine Verts teleosts isosmotic teleosts isosmotic (use gills to remove salt) elasmobranchs close to isosmotic elasmobranchs close to isosmotic mammals hyperosmotic mammals hyperosmotic

Costs and Benefits of different nitrogenous waste products (Table 5.7) n Ammonia: Marine Animals, Inexpensive, water soluble, 1N/molec.(lose less C), permeable thru lipid bilayer, highly toxic n Urea: Expensive (2 ATP), water soluble, 2N/molec., moderately permeable thru lipid bilayer, moderately toxic n Uric Acid: Very Expensive, water insoluble, minimize water loss, not permeable thru lipid bilayer, 4N/molec., Low toxicity

Water and Solute Balance 2 Osmo/Ion-regulatory Organs

Question: n What do osmoregulatory organs of different animals have in common? n In what ways do they differ and why? n What are some key differences between osmoregulation in aquatic and terrestrial environments?

n Most animals have tubular osmoregulatory structures involving the same types of ion uptake and excretion mechanisms (see book) n In aquatic habitats nitrogenous excretion can occur across gills or integument (skin)…will be removed through simple diffusion n In terrestrial habitat osmoregulation and (nitrogenous) excretion is done together…use excess water to remove wastes

Osmoregulatory Organs Contractile vacuolesProtozoans, Sponges None demonstratedCoelenterates (strictly marine) Echinoderms (strictly marine) Nephridial organs Protonephridia (closed ends)Platyhelminthes, Aschelminthes Metanephridia (open ends)Annelids NephridiaMolluscs GutMany animals Antennal glandsCrustaceans Malpighian tubulesInsects KidneysVertebrates GillsCrustaceans, Molluscs, Fishes SkinAmphibians Salt glandsBirds, Reptiles

Common Themes n Tubular structures n Remove or absorb ions n 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 n Contains simple tubular structures n But which are compacted n Around 1 million of these tubules (nephrons) in humans n 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 n Enormous osmo-iono-regulatory capacity n Receives 20-25% of total cardiac output n Osmoregulation n Excretion n Regulate Blood Pressure n pH Balance: produces about 1 liter of slightly acidic urine daily (pH 6.0) (blood maintained at pH 7.4)

Human Kidney

Figure 5.16 The Functional Unit The Nephron

Mammalian Kidney

Countercurrent Multiplier system Na + Cl - are pumped out 3Na +

Countercurrent Multiplier system n Flow moving in opposite directions (countercurrent) n Where the concentration difference is not big between the descending and ascending side of the loop, BUT, along the whole length of the loop, the difference is additive and big (multiplicative)

Countercurrent Multiplier system A mechanism through which water is moved out of the tubule (to conserve water in the organism) Na + Cl -

Countercurrent Multiplier system n A general method for exchange (heat, gas, liquid) n (in this case water and ions) n Creates a concentration gradient along the loop n Requires a loop structure n Common in animals, engineering, gills, lungs n Relies on asymmetry and flow through the tube

Countercurrent Multiplier system Na + Cl - are pumped out And diffuses to the Other side

Countercurrent Multiplier system Impermeable to water Impermeable to solutes The interstitium become concentrated

Countercurrent Multiplier system Impermeable to water Impermeable to solutes Water diffuses out of The descending loop H20H20

Countercurrent Multiplier system Impermeable to water Impermeable to solutes The fluid at the hairpin Becomes more concentrated H20H20

Countercurrent Multiplier system Impermeable to solutes The fluid at the hairpin Becomes more concentrated Which gives the ascending loop more ions to pump out

Countercurrent Multiplier system Impermeable to solutes Which gives the ascending loop more ions to pump out

Countercurrent Multiplier system The fluid at the hairpin Becomes more concentrated H20H20 Which gives the ascending loop more ions to pump out Which causes More water to Diffuse out

Countercurrent Multiplier system H20H20 So with little energy, the fluid becomes Increasingly concentrated

Water and Solute Balance 2 Ionic and Osmotic Regulation in Different Organisms in Different Environments

(3) Ionic and Osmotic Regulation in Different Organisms in Different Environments n Last Time: Inside Cell vs Outside Cell n This Time: Inside the Organism (both intracellular & extracellular fluids) vs The Environment

K+K+ Na + Cl- HCO3- Na + K+K+ Mg ++ Ca ++ Cl - Organic Anions Extracellular Fluids (blood) The Cell Last time we discussed strategies for regulation concentrations in and out of the cell

K+K+ Na + Mg ++ Ca + + Cl - Organic Anions The Cell Cl- HCO3- Na + K+K+ Mg ++ Ca ++ Extracellular Fluids The Environment Now, we want to discuss the interaction between the organism and the Environment

Osmo/Iono-conformers: Osmotic pressure (or ionic concentration) of extracellular fluid (blood) matches that of the environment Osmo/Iono-regulators: Maintain relatively stable blood osmotic pressure (ionic concentration) over a range of pressures (ionic concentrations) in the environment

Hyperregulation Hyporegulation

Daphnia from Lake Mendota Which is most likely to be an Osmo/Iono-conformer?

Differences in Body Fluid Regulation in Different Environments

Evolutionary patterns n Intracellular ionic concentrations are conserved (constraints of basic cell biochemistry) n Extracellular fluids and intra and extra cellular osmotic regulation varies much more

Intracellular differences among species n Ionic composition is more conserved across species (differences related to evolutionary adaptations) n Osmotic concentration differs among species: u Using osmolytes or urea to fill Solute Gap with Environment u Depends on environment u And on Evolutionary History Relatively conserved

Osmotic differences among species n Ionic composition is more conserved across species n Osmotic concentration differs greatly among species: n Need to maintain osmotic constancy in and out of the cell, and then try to approach the osmotic concentration of the environment u Using osmolytes or urea to fill Solute Gap with Environment u Depends on Environment: Extracellular fluids provide a Buffer between the cells and the Environment u And on Evolutionary History Osmotic Concentrations vary

Osmolytes n Organic osmolytes: small solutes used by cells to maintain cell volume n Compatible solutes: does not perturb macromolecules in the cell and are interchangeable (one functions as well as another) n However, not all osmolytes are compatible solutes and some have specific functions (read about in Yancey 2005)

Osmotic Regulation Examples of Osmolytes: n Carbohydrates, such as trehalose, sucrose, and polyhydric alcohols, such as glycerol and mannitol n Free amino acids and their derivatives, including glycine, proline, taurine, and beta-alanine n Urea and methyl amines such as trimethyl amine oxide (TMAO) and betaine

Patterns of osmolyte composition in intracellular fluids Yancey 2005

Extracellular Ionic & osmotic concentrations vary among species in different habitats

Match environment Unusually low Deal with low salinity No longer an osmotic issue

Metabolic Cost of Osmoregulation n The cost of iono- and osmoregulation varies greatly among animals n Depends on gradient between environment and Extracellular fluid n Permeability of the integument (skin) n And particular evolutionary strategy Examples: Low in Marine Invertebrates Marine Teleosts: 8-17% of resting metabolic rate Freshwater teleosts: 3-7% of resting metabolic rate

Marine Invertebrates n Extracellular ionic & osmotic concentrations close to sea water n Some species do not regulate at all n Intracellular ionic concentration conserved (low) n Intracellular osmotic concentration high (Osmotic solute gap filled by osmolytes) n High body permeability to water and ions Isosmotic urine

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

Adaptations to Fresh Water 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? Vertebrates n Low Extracellular ionic AND osmotic concentration n They are osmoregulators, even when they return to marine habitats. n Bones form more readily in Fresh Water (relative large availability of Calcium) n Greater degree of regulation

Elasmobranchs, cartilaginous fishes n Low Extracellular ionic concentration!!! (1/3 of seawater, evolution in fresh water?) urea n Solute gap for BOTH extra and intracellular fluids filled by urea!!! n Some species slightly hyperosmotic (limited osmoregulator, not osmoconformer)

Elasmobranchs, cartilaginous fishes Withers PC Urea: diverse functions of a 'waste' product. Clin Exp Pharmacol Physiol. 25: n Urea is a waste product n It destabilized proteins (but Trimethylamine N-oxide TMAO stabilizes) n Close to isosmotic n Don’t need to drink n Some are slightly hyperosmotic n Water flows into gills (gains the water it needs this way)

n Extracellular fluid (blood) concentration 1/4 of marine animal n More concentrated than freshwater animal n Not have to worry about loss of ions through osmosis (so osmotic conc. can be higher than in fresh water) n Instead, problem of evaporation (water loss through respiration) n Mammals: another issue is water used for thermoregulation (sweat) Terrestrial Vertebrates

Terrestrial Adaptations n Active behavioral uptake of water n Ion uptake from food n Skin and cuticle evolved to prevent water loss n Concentrated Urine (kidneys) n Some terrestrial animals can survive water loss (camel- survive 30% loss)

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