Homeostasis: Homeostasis: Osmoregulation in Osmoregulation in

elasmobranchselasmobranchs

The difference between The difference between marine, eurahyline and marine, eurahyline and

fresh water speciesfresh water species

OsmoregulationOsmoregulation

• Relationship between solute to solvent Relationship between solute to solvent concentrations of internal body fluidsconcentrations of internal body fluids

• The environment the organism lives The environment the organism lives inin

• Isotonic? Isotonic?

• Hypertonic? Hypertonic?

• Hypotonic?Hypotonic?

Osmolarity = solute/solvent concentrationOsmolarity = solute/solvent concentration

water molecules protein molecules

semipermeable membranebetween two compartments

Fig. 5-20, p.86

2% sucrose solution

1 liter of distilled water

1 liter of 10% sucrose

solution

1 liter of 2% sucrose

solution

HypotonicConditions

HypertonicConditions

IsotonicConditions

Fig. 5-21, p.87

first compartment

second compartment

hypertonicsolution

membrane permeableto water but not to solutions

fluid volumerises in secondcompartment

hypotonicsolution

Fig. 5-22, p.87

Stepped ArtStepped Art

HypotonicSolution

membrane permeable towater but not to solutes

HypertonicSolution

Fig. 5-22, p.87

The Challenge• Avoid desiccation in an aqueous Avoid desiccation in an aqueous

environmentenvironment

– MARINE ANIMALSMARINE ANIMALS• DehydrationDehydration• Elimination of excess saltElimination of excess salt

– FRESHWATER ANIMALSFRESHWATER ANIMALS• Conserve saltsConserve salts

• Eliminate excess waterEliminate excess water

Environmental challenges of Environmental challenges of elasmobranchselasmobranchs• All ureotelic and ureosmotic except All ureotelic and ureosmotic except

potamytrygonid rayspotamytrygonid rays• Marine elasmobranchs surrounded by salt; Marine elasmobranchs surrounded by salt;

lose water; lose water; – need to get rid of excess organic and inorganic need to get rid of excess organic and inorganic

compoundscompounds• Euryhaline species environment fluctuatesEuryhaline species environment fluctuates

– Must handle salt and fresh conditions Must handle salt and fresh conditions • Freshwater speciesFreshwater species

– lose salt and electrolytes; need to get rid of lose salt and electrolytes; need to get rid of excess waterexcess water

Dealing with Environment

• Marine : Maintain serum osmolarity = or Marine : Maintain serum osmolarity = or greater than seawater primarily w/ ureagreater than seawater primarily w/ urea– Little osmotic loss of waterLittle osmotic loss of water

• Dilute Seawater or Freshwater: Serum Dilute Seawater or Freshwater: Serum osmolarity reducedosmolarity reduced– Little diffusion of water inwardLittle diffusion of water inward

Players in osmoregulation Players in osmoregulation

• OrgansOrgans– Kidney, liver, gills, rectal glandKidney, liver, gills, rectal gland

• Organic compoundsOrganic compounds– UreaUrea– TMAO trimethylamine oxideTMAO trimethylamine oxide

• Inorganic ionsInorganic ions– SodiumSodium– ChlorideChloride– Other saltsOther salts

Umanitoba - Gary Anderson

Body FluidBody FluidMarine ElasmobranchsMarine Elasmobranchs

• Reabsorb & retain urea and other Reabsorb & retain urea and other body fluid solutes in tissuesbody fluid solutes in tissues

- Serum osmolarity remains just Serum osmolarity remains just greater than external seawater greater than external seawater (hyperosmotic)(hyperosmotic)

- Don’t have to drink water like Don’t have to drink water like teleoststeleosts

- Water gained excreted by kidneysWater gained excreted by kidneys• Tri-MethylAmine Oxide (TMAO): Acts to Tri-MethylAmine Oxide (TMAO): Acts to counteract the perturbing effects of ureacounteract the perturbing effects of urea

Marine elasmobranchsMarine elasmobranchsPlasma solutes and Plasma solutes and osmoregulationosmoregulation• Different than marine teleostsDifferent than marine teleosts• Have high osmolarityHave high osmolarity• Reabsorb and retain high levels of urea and TMAO Reabsorb and retain high levels of urea and TMAO

in their body fluidsin their body fluids• Osmolarity remains hyperosmotic to surrounding Osmolarity remains hyperosmotic to surrounding

seawaterseawater• TMAO to stabilize proteins and activate enzymesTMAO to stabilize proteins and activate enzymes• Water gained across gills is excreted by kidneysWater gained across gills is excreted by kidneys• Any salt gained across gills is excreted by rectal Any salt gained across gills is excreted by rectal

gland and kidneygland and kidney

Body fluid of euryhaline Body fluid of euryhaline elasmobranchselasmobranchs

• Ammonotelic in frehwaterAmmonotelic in frehwater• As salinity increasesAs salinity increases

– Increase urea production and retention Increase urea production and retention – Decrease urea excretionDecrease urea excretion– Increase Na+ and Cl- Increase Na+ and Cl- – Decrease ammonia excretionDecrease ammonia excretion

• Can not produce and retain as much urea Can not produce and retain as much urea as marine spp. (lower osmolarity)as marine spp. (lower osmolarity)

• Ex. Ex. D. sabina and H. signifierD. sabina and H. signifier

Body fluid of euryhaline Body fluid of euryhaline elasmobranchselasmobranchs

As salinity decreasesAs salinity decreases• Lower osmolarity (less urea and TMAO) Lower osmolarity (less urea and TMAO)

than marine speciesthan marine species• Decrease amount of urea produced and Decrease amount of urea produced and

reabsorbedreabsorbed• Increased urinary excretionIncreased urinary excretion• Loss of sodium and chloride balanced by Loss of sodium and chloride balanced by

electrolyte uptake at the gills and electrolyte uptake at the gills and reabsorbed by kidneys reabsorbed by kidneys

Bull Shark - Bull Shark - Carcharhinus Carcharhinus leucasleucas

Eeigen Werk

Body FluidFresh Water Elasmobranchs

• Lost ability to synthesize and retain urea or Lost ability to synthesize and retain urea or TMAO TMAO

• Body fluid solute concentrations relatively lowBody fluid solute concentrations relatively low

• Freshwater rays abandoned renal Freshwater rays abandoned renal reabsorptionreabsorption- Urine is diluteUrine is dilute- AmmonotelicAmmonotelic

- Ex. Ex. Potamotrygon Potamotrygon raysrays

PotamotrygonidaePotamotrygonidae

Raimond Spekking

Urea- production, retention Urea- production, retention and reabsorptionand reabsorption

• Urea productionUrea production– Occurs in the liverOccurs in the liver

• RetentionRetention– In gillsIn gills

• ReabsorptionReabsorption– In kidneysIn kidneys

Urea production in liverUrea production in liver

Ornithine-urea cycle (OUC)Ornithine-urea cycle (OUC)– Glutamine synthetase is crucial enzyme Glutamine synthetase is crucial enzyme

needed for urea productionneeded for urea production– Euryhaline spp. decrease production of urea Euryhaline spp. decrease production of urea

when entering fresh waterwhen entering fresh water– Freshwater rays lack the enzyme for the Freshwater rays lack the enzyme for the

biosynthesis to occurbiosynthesis to occur– Unsure if urea is produced in other locationsUnsure if urea is produced in other locations– Bacteria hypothesized for being responsibleBacteria hypothesized for being responsible

Marine gills retain ureaMarine gills retain urea

• Do not lose much urea across gills Do not lose much urea across gills • Gill’s basolateral membrane has high Gill’s basolateral membrane has high

cholesterol to phospholipid ratio levelscholesterol to phospholipid ratio levels– Membrane limit diffusionMembrane limit diffusion

• Active transport of urea by Na+/ urea Active transport of urea by Na+/ urea antiporter energized by Na+/K+ antiporter energized by Na+/K+ ATPasesATPases

• Used more for salt regulation and Used more for salt regulation and acid/base balanceacid/base balance

Kidneys reabsorb ureaKidneys reabsorb urea

• Reabsorption contributes to high urea levelsReabsorption contributes to high urea levels• Minor site of urea lossMinor site of urea loss• Thought to involve active transportThought to involve active transport• Use urea-sodium pumpUse urea-sodium pump• Proven in Proven in R. erinaceaR. erinacea• Second hypothesis for passive transport that has Second hypothesis for passive transport that has

not been provennot been proven• Euryhaline spp. decrease renal reabsorption of Euryhaline spp. decrease renal reabsorption of

urea as enter areas of decreased salinityurea as enter areas of decreased salinity– Increases rate of urine flow to rid system of excess ureaIncreases rate of urine flow to rid system of excess urea

Salt regulationSalt regulation

• Rectal gland secretionsRectal gland secretions– Marine spp. surrounded by high salinity Marine spp. surrounded by high salinity – Rectal gland secretes sodium and Rectal gland secretes sodium and

chloridechloride– Na+/ K+ ATPases used Na+/ K+ ATPases used

Osmoregulation by the Osmoregulation by the Rectal GlandRectal Gland

• Rectal Gland = Salt secreting Rectal Gland = Salt secreting mechanismmechanism– Migratory elasmos - regressive rectal Migratory elasmos - regressive rectal

glandgland– Non-functional in freshwater raysNon-functional in freshwater rays

http://fig.cox.miami.edu/~cmallery/150/physiol/rectal.htm

Salt regulation Salt regulation

• GillsGills– Salt uptakeSalt uptake

•Na+/ K+ ATPases even higher in freshwaterNa+/ K+ ATPases even higher in freshwater

– Acid/ base balanceAcid/ base balance•Secrete acidSecrete acid

•H+ excreted/exchanged for Na+H+ excreted/exchanged for Na+

•Run by Na+/ K+ ATPases Run by Na+/ K+ ATPases

– Responsible for ammmonia secretionResponsible for ammmonia secretion

Salt regulationSalt regulation

• Kidney salt excretionKidney salt excretion– Dilute environmentDilute environment

•Urine flow increaseUrine flow increase

– SaltwaterSaltwater•Not solely responsible for salt secretionNot solely responsible for salt secretion

Endocrine Regulation to Endocrine Regulation to Regulate Body Fluid Volume Regulate Body Fluid Volume

and Solute Concentrationand Solute Concentration• CNP - Released from heart CNP - Released from heart

– Increase urine productionIncrease urine production– Stimulate salt secretion from rectal glandStimulate salt secretion from rectal gland– Inhibit drinking and relax blood vessels Inhibit drinking and relax blood vessels

• AVT AVT – Increase in plasma osmolalityIncrease in plasma osmolality– Reduces urine productionReduces urine production

• RASRAS– Antagonistic to CNP, reduces urine flowAntagonistic to CNP, reduces urine flow– Increases drinking Increases drinking – Constricts blood vesselsConstricts blood vessels

Feeding and osmoregulationFeeding and osmoregulation

• Urea is metabolically expensiveUrea is metabolically expensive– 5 umol ATP for 1 mole urea5 umol ATP for 1 mole urea

• Protein in food is main source of N in Protein in food is main source of N in ureaurea

• Elasmobranches must get adequate Elasmobranches must get adequate food to produce the ureafood to produce the urea

• Why ureotelic and not Why ureotelic and not ammonotelic???ammonotelic???

Literture citedLiterture cited

• Hammerschlag Hammerschlag N.2006. N.2006. Osmoregulation in elasmobranches: a review for fish Osmoregulation in elasmobranches: a review for fish biologists, biologists, behaviorists and ecologistsbehaviorists and ecologists.  MARINE AND FRESHWATER MARINE AND FRESHWATER BEHAVIOUR AND BEHAVIOUR AND PHYSIOLOGY 39 (3): 209-228 PHYSIOLOGY 39 (3): 209-228

• Speers-Roesch B, Ip YK, Ballantyne JS.2006. Metabolic organization of freshwater, Speers-Roesch B, Ip YK, Ballantyne JS.2006. Metabolic organization of freshwater, euryhaline, and marine elasmobraches: implications for the evolution of euryhaline, and marine elasmobraches: implications for the evolution of

energy energy metabolism inmetabolism in sharks andsharks and rays. JOURNAL OF EXPERIMENTAL BIOLOGY 209 rays. JOURNAL OF EXPERIMENTAL BIOLOGY 209 (13): 2495-(13): 2495- 2508 2508

•Pillans RD, Anderson WG, Good JP, et al.2006. Plasma and erythrocyte solute Pillans RD, Anderson WG, Good JP, et al.2006. Plasma and erythrocyte solute properties of properties of juvenile bull sharks, Carcharhinus leucas, acutely exposed to juvenile bull sharks, Carcharhinus leucas, acutely exposed to increasing environmental increasing environmental salinity. salinity.

JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY 331 (2): 145-JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY 331 (2): 145-157 157

• Pillans RD, Good JP, Anderson WG, et al. 2005.Freshwater to seawater acclimation of Pillans RD, Good JP, Anderson WG, et al. 2005.Freshwater to seawater acclimation of juvenile bull juvenile bull sharks (Carcharhinus leucas): plasma osmolytes and Na+/K+ sharks (Carcharhinus leucas): plasma osmolytes and Na+/K+ ATPase activity in gill, rectal ATPase activity in gill, rectal gland, kidney and intestine. JOURNAL OF gland, kidney and intestine. JOURNAL OF COMPARATIVE PHYSIOLOGY B-BIOCHEMICAL COMPARATIVE PHYSIOLOGY B-BIOCHEMICAL SYSTEMIC AND ENVIRONMENTAL SYSTEMIC AND ENVIRONMENTAL PHYSIOLOGY 175 (1): 37-44PHYSIOLOGY 175 (1): 37-44

Literature citedLiterature cited

• Pillans RD, Franklin CE.2004. Plasma Pillans RD, Franklin CE.2004. Plasma osmolyte concentrations and rectal osmolyte concentrations and rectal gland mass of bull sharks gland mass of bull sharks

Carcharhinus Carcharhinus leucas, captured leucas, captured along a salinity along a salinity gradient. gradient. COMPARATIVE COMPARATIVE BIOCHEMISTRY AND BIOCHEMISTRY AND PHYSIOLOGY A-PHYSIOLOGY A- MOLECULAR & MOLECULAR & INTEGRATIVE INTEGRATIVE PHYSIOLOGY 138 (3): PHYSIOLOGY 138 (3): 363-363-