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BIO224 - ichthyology > osmoregulation > Flashcards

osmoregulation Flashcards

1
Q

how does Osmotic pressure/salinity tend to change

A

by location
- External environment (prone to wide fluctuation)
- Intracellular environment (allows for no variation; HOMEOSTASIS)
- Extracellular environment maintains balance between the two (blood, lymph fluid etc.)

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2
Q

what is homeostasis

A

Maintaining a steady state equilibrium in the internal environment of an organism
- Much of homeostasis is involuntary by action of hormones, enzymes and osmoregulatory processes
- Although occasionally fish do just “pick up and move” if environmental conditions are unfavourable

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3
Q

what is osmoregulation

A

the active regulation of the osmotic pressure of an organism’s fluids to maintain the homeostasis of the organism’s water content

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4
Q

what’s the problem with homeostasis in fish

A
  • Homeostasis requires the concentrations of internal water and solutes to be maintained within fairly narrow limits, however…
  • Physiological systems of fishes operate in an internal fluid environment that may not match their external fluid environment
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5
Q

what is Molarity

A

the amount of substance (1 mol) per volume (1 litre) of solution

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6
Q

what is Molality

A

the amount of substance (1 mol) per weight (1 kg) of solution

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7
Q

what is osmosis

A

the movement of water across a semi-permeable membrane as a result of varying concentrations of dissociated molecules (salts, proteins, ions)

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8
Q

what determines wether water will move across the membrane or not

A

osmolarity (osmotic pressure)
- Greater osmolarity = lower osmotic pressure
-Something very salty = low osmotic pressure
-Pure water = high osmotic pressure
- Water flows from high to low pressure

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9
Q

what is Isosmotic

A

2 solutions that exert the same osmotic pressure
- Intracellular osmolarity = External osmolarity
- No water lost or gained: OSMOCONFORMER
- Many marine invertebrates

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10
Q

what is Hyperosmotic

A

a solution that exerts a lower osmotic pressure and so attracts water
- Intracellular osmolarity > External osmolarity (saltier than water around you)
- Tissues gain water: OSMOREGULATOR
- Freshwater fish

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11
Q

what is Hyposmotic

A

a solution that exerts a greater osmotic pressure and so loses water
- Intracellular osmolarity < External osmolarity (less salty than water around you)
- Tissues lose water: OSMOREGULATOR
- Marine teleosts

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12
Q

what are the chief organs of excretion/osmoregulation

A

gills
**Kidneys first evolved as osmoregulatory organs in fishes to remove water

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13
Q

4 osmoregulatory functions in fish

A
  • Isosmotic (nearly isoionic; osmoconformers)
  • Hyperosmotic with regulation of specific ions – has strategy to be hypersmotic to live in that environment (elasmobranchs)
  • Hyposmotic (marine fish)
  • Hyperosmotic (freshwater fish)
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14
Q

explain Isosmotic function

A

Osmoconformers (no strategy)
- Hagfishes
- Internal salt concentration = seawater
- However, since they live IN the ocean….no regulation required!
- Only vertebrate that is isotonic to seawater - much like many marine invertebrates

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15
Q

explain Hyperosmotic with regulation of specific ions

A
  • Elasmobranchs
  • Internal salt concentration ~ 1/2 seawater (hyposmotic)
  • BUT additional 1/2 of internal osmolarity made up of urea
  • So total internal osmotic concentration is slightly greater than seawater (hyperosmotic)
  • Gill membrane has low permeability to urea so it is retained within the fish
  • Because internal inorganic and organic salt concentrations mimic that of their environment, passive water influx or efflux is minimized
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16
Q

explain Ionic and osmoregulation in marine elasmobranchs

A
  • Body fluids = 1100 mOsm/kg
  • External environment = 1000 mOsm/kg
  • Slightly hyperosmotic – gain water
  • Less energy required than freshwater fish to maintain this balance
  • Maintain high solutes
  • Slightly hyperosmotic body fluids by retaining some nitrogenous solutes - especially Urea, Betaine, Sarcosine and some amino acids (Taurine and β-alanine)
  • Skin and gills of elasmobranchs impervious to urea (don’t excrete it)
  • Monovalent ions enter the body and are excreted by the RECTAL GLAND (very similar function to chloride cells)
17
Q

impact of urea in elasmobranchs

A
  • Urea concentration 0.4 M in blood of elasmobranchs - 100x concentration that most vertebrates would die from!!!!
  • Some proteins and enzymes actually need a high urea concentration to function efficiently, others are resistant to effects of urea
  • Trimethylamine oxide (TMAO) and other methylamine substances protect proteins from urea
  • THE ENTIRE METABOLISM OF SHARKS IS ADAPTED TO THE PRESENCE OF UREA
  • Freshwater species have less conc of salt ions + especially urea
18
Q

explain Hyposmotic

A
  • Marine teleosts
  • Intracellular osmolarity < External osmolarity (Tissues lose water)
  • Ionic conc. ~ 1/3 of seawater
  • Drink copiously to gain water
  • Drinking rates in marine fish = very high - But drinking saline water causes dehydration due to increased salt loading – need to excrude/excrete these salts
  • Chloride cells eliminate Na+ and Cl-
  • Kidneys eliminate Mg++ and SO4–
19
Q

what’s the issue with fish drinking to gain water and what’s the solution

A

absorption in the gut is still against an osmotic gradient
- MECHANISM = Solute-linked water transport - water can be absorbed if linked to monovalent ions (single charge Na+, K+ and Cl-)
- Not all solutes are absorbed by the alimentary canal
- Absorbed water has a solute loading ½ seawater (½ osmolarity) - got rid of half the ions in the seawater
but still have an excess of monovalent ions in the fish

20
Q

monovalent ions vs Divalent ions

A
  • monovalent ions (single charge Na+, K+ and Cl-)
  • divalent ions = double charged e.g. Mg++, Ca++
21
Q

explain Ion exchange and osmoregulation in a marine teleost

A
  • Body fluids = 400 mOsm/kg
  • Sea environment = 1000 ~mOsm/kg
  • fish loses water through skin and gills
  • Fish drinks water to compensate for water loss – but full of salt
  • Divalent ions get excreted in faeces
  • Active excretion of monovalent ions via chloride cells (Solute-linked water transport)
22
Q

explain the process that goes on in Saltwater teleosts

A
  1. Loss of water across gills – osmosis
  2. Salts diffuse into blood across gill epethelium
  3. Fish drinks seawater – comes with loads of salt ions but also divalent ions (magnesium + sulfate)
  4. A lot of divalent ions will pass through alimentary canal and get excreted as feaces (not part of Solute-linked transport process) - ones with a diffusion gradient will get passed through kidneys
  5. Salt ions removed actively by chloride cells (contain concentration gradient)
23
Q

explain how Salt ions get removed actively by chloride cells in marine teleosts

A
  1. Carrier protein allows salt ions to enter the chloride cell (passive)
  2. Sodium-potassium pump (active) swaps the positive ions – pumps out Na, replaces with K
  3. Loads of K now is in the chloride cell + little outside
  4. K diffuses out of the cell passively (concentration + electrochemical gradient)
  5. Net negative charge is left in the cell (Cl) - leaves electrochemical gradient for chloride to diffuse out
  6. Abundance of Na outside chloride cell will diffuse back into seawater – higher conc of Na than seawater
24
Q

explain Hyperosmotic

A
  • Freshwater fish
  • intracellular osmolarity > External osmolarity (Tissues gain water )
  • Freshwater animals constantly take in water by osmosis from their environment
  • They lose salts by diffusion and maintain water balance by excreting large amounts of dilute urine
  • Salts lost by diffusion are replaced in foods and by active uptake across the gills
25
Q

explain Osmotic regulation by freshwater teleosts

A
  • Ionic conc. approx 1/3 of seawater
  • Do not drink (much)
  • ß-CHLORIDE CELLS (fewer, work in reverse to chloride cells)
  • Kidneys eliminate excess water (ion loss, however – need to be replaced)
  • Loss of salts in urine is balanced by active uptake - Ammonium and bicarbonate ion exchange mechanisms
26
Q

explain the Ammonium and bicarbonate ion exchange mechanisms in freshwater teleosts

A

(ß-CHLORIDE CELLS)
1. Active pumps on gill membrane swap ammonium or protons (H+) for Na+
2. Bicarbonate can also be swapped for Cl- ions

27
Q

explain the process that goes on in freshwater teleosts

A

1.Influx of water (osmosis) + loss of ions (diffusion)
2. have to get rid of the water entering their system using their kidneys
3. Ion exchange pumps on beta chloride cells to scavenge monovalent ions to the water around them

28
Q

explain Ion exchange and osmoregulation in a freshwater fish

A

Body fluids = 300 mOsm/kg
Sea environment = 5 mOsm/kg
1. Water gain over skin and gills, salt loss by diffusion
2. Copious dilute urine, so some loss of ions in faeces
3. Replace ions by eating + Active uptake of monovalent ions via chloride cells

29
Q

why do Freshwater fish face problem of water coming into their tissues

A

Diffusion through skin can be limited:
-Scales
-Thick, relatively impermeable skin, mucous
- Gills always have a thin blood-barrier, however… (compared to other tissues)

30
Q

how do freshwater teleosts Deal with water uptake

A
  • Drinking rates low; but passive diffusion in of water from environment
  • Large Bowman’s capsule (part of the kidney) and many glomeruli for efficiently filtering water out of blood
  • Glucose is reabsorbed in proximal tubule of kidney
    99% of salts reabsorbed in distal tubule and bladder
31
Q

what are Euryhaline fish

A

Can tolerate a wide range of salinities eg. intertidal fish, estuarine fish

32
Q

what are Stenohaline fish

A

Have little tolerance to varying salinity eg. most fish, both freshwater and marine

33
Q

what are Euryhaline conditions

A

Short-term fluctuations in osmotic state of environment, e.g. in intertidal zone or in estuaries where salinity can range from 10 to 34 with the daily tidal cycle

34
Q

how do fish deal with Euryhaline conditions

A

Fish have both kinds of chloride cells
 when salinity is low, operate more like FW fishes
 when salinity is high, operate like marine fishes
 kidneys function only under low salinity conditions

35
Q

adaptations to Diadromous fishes (spend part of life in salt water, part in freshwater)

A
  • convert from FW adaptations to SW or vice versa, depending on direction of migration
  • These fish inhabit two very different environments, each with little variation in salinity, but have long-term adaptations for the change from one to the other
36
Q

what are Less salty species more at risk of and what is the solution

A

freezing e.g marine teleosts
- Macromolecular antifreeze compounds: peptides (protein) + Glycopeptides (carbohydrate/protein)
- both rich in alanine
- Molecules attach to ice crystal surface and interfere with ice crystal growth (disrupt matrix)
- Important - Ice ruptures cells; hinders osmoregulation

37
Q

what accentuates the normal osmoregulatory challenge for freshwater or marine fishes and what is the solution

A
  • Stressors (handling, sustained exercise e.g. escape from predator pursuit) cause release of adrenaline (epinephrine)
  • Adrenaline causes diffusivity of gill epithelium to increase (become “leaky” of water and ions)
  • Can minimise the osmotic challenge by placing fish in conditions that are closer to isosmotic
     add salt to freshwater
     dilute saltwater with freshwater

BIO224 - ichthyology (13 decks)

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