Transcript Homeostasis: Osmoregulation in elasmobranchs

Homeostasis: Osmoregulation in
elasmobranchs
The difference between
marine, eurahyline and fresh
water species
Osmoregulation
• Relationship between solute to solvent
concentrations of internal body fluids
• The environment the organism lives in
• Isotonic?
• Hypertonic?
• Hypotonic?
Osmolarity = solute/solvent concentration
water molecules
protein molecules
semipermeable membrane
between two compartments
Fig. 5-20, p.86
2%
sucrose
solution
1 liter of
distilled water
Hypotonic
Conditions
1 liter of
10% sucrose
solution
1 liter of
2% sucrose
solution
Hypertonic
Conditions
Isotonic
Conditions
Fig. 5-21, p.87
first
compartment
hypotonic
solution
second
compartment
hypertonic
solution
membrane
permeable
to water but
not to
solutions
fluid volume
rises in second
compartment
Fig. 5-22, p.87
Hypotonic
Solution
Hypertonic
Solution
membrane permeable to
water but not to solutes
Stepped Art
Fig. 5-22, p.87
The Challenge
• Avoid desiccation in an aqueous environment
– MARINE ANIMALS
• Dehydration
• Elimination of excess salt
– FRESHWATER ANIMALS
• Conserve salts
• Eliminate excess water
Environmental challenges of
elasmobranchs
• All ureotelic and ureosmotic except
•
potamytrygonid rays
Marine elasmobranchs surrounded by salt; lose
water;
– need to get rid of excess organic and inorganic
compounds
• Euryhaline species environment fluctuates
– Must handle salt and fresh conditions
• Freshwater species
– lose salt and electrolytes; need to get rid of excess
water
Dealing with Environment
• Marine : Maintain serum osmolarity = or
greater than seawater primarily w/ urea
– Little osmotic loss of water
• Dilute Seawater or Freshwater: Serum
osmolarity reduced
– Little diffusion of water inward
Players in osmoregulation
• Organs
– Kidney, liver, gills, rectal gland
• Organic compounds
– Urea
– TMAO trimethylamine oxide
• Inorganic ions
– Sodium
– Chloride
– Other salts
Umanitoba - Gary Anderson
Body Fluid
Marine Elasmobranchs
• Reabsorb & retain urea and other body
fluid solutes in tissues
- Serum osmolarity remains just greater
than external seawater (hyperosmotic)
- Don’t have to drink water like teleosts
- Water gained excreted by kidneys
• Tri-MethylAmine Oxide (TMAO): Acts to
counteract the perturbing effects of urea
Marine elasmobranchs
Plasma solutes and osmoregulation
•
•
•
•
•
•
•
Different than marine teleosts
Have high osmolarity
Reabsorb and retain high levels of urea and TMAO in
their body fluids
Osmolarity remains hyperosmotic to surrounding
seawater
TMAO to stabilize proteins and activate enzymes
Water gained across gills is excreted by kidneys
Any salt gained across gills is excreted by rectal gland
and kidney
Body fluid of euryhaline
elasmobranchs
• Ammonotelic in frehwater
• As salinity increases
–
–
–
–
Increase urea production and retention
Decrease urea excretion
Increase Na+ and ClDecrease ammonia excretion
• Can not produce and retain as much urea as
•
marine spp. (lower osmolarity)
Ex. D. sabina and H. signifier
Body fluid of euryhaline
elasmobranchs
As salinity decreases
• Lower osmolarity (less urea and TMAO) than
marine species
• Decrease amount of urea produced and
reabsorbed
• Increased urinary excretion
• Loss of sodium and chloride balanced by
electrolyte uptake at the gills and reabsorbed by
kidneys
Bull Shark - Carcharhinus leucas
Eeigen Werk
Body Fluid
Fresh Water Elasmobranchs
• Lost ability to synthesize and retain urea or
TMAO
• Body fluid solute concentrations relatively low
• Freshwater rays abandoned renal reabsorption
- Urine is dilute
- Ammonotelic
- Ex. Potamotrygon rays
Potamotrygonidae
Raimond Spekking
Urea- production, retention and
reabsorption
• Urea production
– Occurs in the liver
• Retention
– In gills
• Reabsorption
– In kidneys
Urea production in liver
Ornithine-urea cycle (OUC)
– Glutamine synthetase is crucial enzyme
needed for urea production
– Euryhaline spp. decrease production of urea
when entering fresh water
– Freshwater rays lack the enzyme for the
biosynthesis to occur
– Unsure if urea is produced in other locations
– Bacteria hypothesized for being responsible
Marine gills retain urea
• Do not lose much urea across gills
• Gill’s basolateral membrane has high
cholesterol to phospholipid ratio levels
– Membrane limit diffusion
• Active transport of urea by Na+/ urea
antiporter energized by Na+/K+ ATPases
• Used more for salt regulation and
acid/base balance
Kidneys reabsorb urea
•
•
•
•
•
•
Reabsorption contributes to high urea levels
Minor site of urea loss
Thought to involve active transport
Use urea-sodium pump
Proven in R. erinacea
Second hypothesis for passive transport that has not
been proven
• Euryhaline spp. decrease renal reabsorption of urea as
enter areas of decreased salinity
– Increases rate of urine flow to rid system of excess urea
Salt regulation
• Rectal gland secretions
– Marine spp. surrounded by high salinity
– Rectal gland secretes sodium and chloride
– Na+/ K+ ATPases used
Osmoregulation by the Rectal
Gland
• Rectal Gland = Salt secreting mechanism
– Migratory elasmos - regressive rectal gland
– Non-functional in freshwater rays
http://fig.cox.miami.edu/~cmallery/150/physiol/rectal.htm
Salt regulation
• Gills
– Salt uptake
• Na+/ K+ ATPases even higher in freshwater
– Acid/ base balance
• Secrete acid
• H+ excreted/exchanged for Na+
• Run by Na+/ K+ ATPases
– Responsible for ammmonia secretion
Salt regulation
• Kidney salt excretion
– Dilute environment
• Urine flow increase
– Saltwater
• Not solely responsible for salt secretion
Endocrine Regulation to
Regulate Body Fluid Volume and
Solute Concentration
• CNP - Released from heart
– Increase urine production
– Stimulate salt secretion from rectal gland
– Inhibit drinking and relax blood vessels
• AVT
– Increase in plasma osmolality
– Reduces urine production
• RAS
– Antagonistic to CNP, reduces urine flow
– Increases drinking
– Constricts blood vessels
Feeding and osmoregulation
• Urea is metabolically expensive
– 5 umol ATP for 1 mole urea
• Protein in food is main source of N in urea
• Elasmobranches must get adequate food
to produce the urea
• Why ureotelic and not ammonotelic???
Literture cited
•
Hammerschlag N.2006. Osmoregulation in elasmobranches: a review for fish biologists,
behaviorists and ecologists. MARINE AND FRESHWATER BEHAVIOUR AND
PHYSIOLOGY 39 (3): 209-228
•
Speers-Roesch B, Ip YK, Ballantyne JS.2006. Metabolic organization of freshwater,
euryhaline, and marine elasmobraches: implications for the evolution of energy
•
•
metabolism in sharks and rays. JOURNAL OF EXPERIMENTAL BIOLOGY 209 (13): 24952508
Pillans RD, Anderson WG, Good JP, et al.2006. Plasma and erythrocyte solute properties of
juvenile bull sharks, Carcharhinus leucas, acutely exposed to increasing environmental
salinity.
JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY 331 (2): 145-157
Pillans RD, Good JP, Anderson WG, et al. 2005.Freshwater to seawater acclimation of juvenile bull
sharks (Carcharhinus leucas): plasma osmolytes and Na+/K+ ATPase activity in gill, rectal
gland, kidney and intestine. JOURNAL OF COMPARATIVE PHYSIOLOGY B-BIOCHEMICAL
SYSTEMIC AND ENVIRONMENTAL PHYSIOLOGY 175 (1): 37-44
Literature cited
• Pillans RD, Franklin CE.2004. Plasma
osmolyte concentrations and rectal
gland mass of bull sharks Carcharhinus
leucas, captured along a salinity
gradient. COMPARATIVE
BIOCHEMISTRY AND PHYSIOLOGY AMOLECULAR & INTEGRATIVE
PHYSIOLOGY 138 (3): 363-