Salinity Flashcards
salinity regulation within invertebrates
bladder -> tubule -> labrynth -> end sac
osmoconformers
salinity regulation within bony fish
osmoregulation is very similar to mammalian osmoregulatory systems (glomerulus etc)
Why regulate salinity
- Important within muscle fibres that facilitate contraction and relaxation – muscle cramp caused by imbalance of ion balance within tissues
- Therefore we need to regulate electrolytes
osmoregulation
maintains electrolyte and fluid homeostasis by active regulation of osmotic pressure of bodily fluids
excretion
process of getting rid of metabolic waste
Ammoniotelic animals
most aquatic animals secrete ammonia unlike mammals and cartilaginous fish that excrete urea
requirement of excreting ammonia
Excretion of ammonia requires water.
How is ionic and osmotic composition linked to excretion
Regulation of the ionic and osmotic composition of body fluids is intimately linked with nitrogenous excretion – osmosis is a key process within this excretion
* Isosmotic situation is the most desirable
marine invertebrate fluid composition
-Similar composition to that of the sea water around them
-Osmotic concentration is close to their medium and do not experience significant water loss or gain
Osmoconformers
Overall osmotic concentration is always approximately isosmotic (same osmotic pressure) with seawater
Strategies of osmoconformity
- Body volumes changes as water enters and leaves by osmosis at least in the short term
- In the long-term, volume may adjust towards original level as both ions and water move
- Cell volume tends to be slowly adjusted by regulating free amino acid pool
Osmoregulators
- Regulate ionic and osmotic compositions of their body fluids to maintain a stable internal fluid composition
- Migratory fish and some estuarine invertebrates
Euryhaline animals
- Tolerate a wide range of salinities – combo of osmoconforming and osmoregulatory processes
Stenohaline
- Restricted to a narrow salinity range
- Still have active ionic and osmotic regulators
- Most marine organisms
Intracellular osmotic regulation
- Cells are isosmotic to bodily fluids but have a different ion composition
- If osmotic conc of body fluid changes this is matched by changes of organic molecules in cells
- Organic molecules are used inside cells as osmoregulators
Marine invertebrate intracellular regulation molecule
the amino acid glycine
Conflict of using amino acids as osmotic regulators
- May interact with proteins and change their conformation
- Enzymes and other proteins are sensitive to change in ionic composition of the intracellular fluids
amino acids - Salinity mediated osmoregulation
- Conc of free amino acids in cells is regulated by changing levels of protein degradation or synthesis
- Concentration increases during salinity stress
- Salinity induced alterations in amino acid bases are caused by adjustments consistent with cell volume regulation
Marine vertebrates ways of osmotic regulation
- Isosmotic with sea water
- Hypoosmotic regulators (most vertebrates)
- Air breathing marine vertebrates (no gills)
Hypoosmotic – marine teleost
- Body fluid of teleost only ¼ to 1/3 of seawater concentration in both seawater and freshwater species
- Marine teliosts lose water by osmosis from gills but compensate by drinking water
- Excess nacl secreted at gills
- Active transport of cl- by large chloride cells in gill epithelium and Na+ follows passively
- Fish kidneys cannot form conc urine but excrete divalent ions Mg+2 and SO42- (with minimal loss of water -> small volume of isotonic urine)
Salmon - hypoosmotic
- Salmon migrate between oceans and freshwater
- At sea – drink seawater, excrete salt from gills and produce little urine
- In freshwater – stop drinking, take in salt via gills and produce lots of dilute urine (hyperosmotic that why they stop drinking)
Air breathing marine vertebrates
Essentially operate as terrestrial for osmoregulation – isolated from seawater as no gills
* Face more problems than fully terrestrial species as no freshwater to drink & high salts in food (algae & invertebrates isosmotic to seawater)
Marine mammals
- Able to form hyperosmotic urine (more conc than seawtaer)
- ALLOWS REMOVAL EXCESS of salts from food or ingested seawater
- Humans cannot tolerate this
- Whale has net gain of 1/3 litre water, while human has net loss of 1/3 litre water if human drinks seawater
- Human urine is less concentrated than seawater, so drinking it hastens death
Mechanism of excretion in invertebrates
- Lower invertebrates still rely on diffusion to remove nitrogenous waste
- Higher invertebrates have a tubular filtration system
3 basic processes that occur in a tubular system
reabsorption filtration and excretion
excretory system overview
- Systems of tubules are spread throughout the body
- Beating cilia at the closed end of the tube draw intestinal fluid into the tubule
- Excess fluid exits through skin
- Solutes are reabsorbed before dilute urine is excreted
More complex excrete systems
- Simple tubular excretory system
- Internal openings or nephrostomes collect coelomic fluid when the cilia present on the funnel shaped opening beat
- Metanephridia have both excretory and osmoregulatory functions
- Excrete water, mineral, salts and nitrogenous waste in the form of urea
Crustacea excretory system
- Antennal gland consists of a bulb like sac (‘end sac’) called the ‘coelomosac’ connected to the ‘labyrinth’ – a narrow tubular ‘nephridial canal’ joins the labyrinth and a bladder
- Structures are also osmotically active – urine (ammonia) is first formed in the lumen of the coelomosac and is sent out through the bladder at the base of the second antenna
What is the approximate osmotic concentration of the body fluids of an
osmoregulating fish?
~ 200mM Na+ in teleosts, balance of osmotic pressure sometimes maintained with
urea to 600-700mM
