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MST2102 > Osmoregulation > Flashcards

Osmoregulation Flashcards

1
Q

•Osmoconformer

A

•Osmoconformer - body fluid isosmotic with surrounding sea water.

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2
Q

•Osmoregulator

A

•Osmoregulator - body fluid not isosmotic with sea water.

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3
Q

Solute composition

A

•Solute composition - the dissolved substances (ions, proteins, etc.) in the body fluid.

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4
Q

Haemolymph

A

•Haemolymph - body fluid contained in the primary body cavity (the haemocoele), this is the main body fluid in the Mollusca & Crustacea.

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5
Q

Coelomic fluid

A

•Coelomic fluid - body fluid contained in the secondary body cavity (the coelom), this is the main body fluid in the annelids, echinoderms and cephalopod molluscs.

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6
Q

Osmolarity

A

•Osmolarity – now known as osmotic concentration, it is the measure of solute concentration, defined as the number of osmoles (Osm) of solute per litre (L) of solution (OsmL-1)

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7
Q

Osmolality

A

•Osmolality – a variation of molality that takes into account only solutes that contribute to a solution’s osmotic pressure (Osmkg-1)

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8
Q

Give the main solute composition in seawater

A
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9
Q

What is the Donnan Equilibrium?

A
  • The presence of a non-diffusible ion (e.g. a protein) on one side of a semi-permeable membrane can lead to an unequal distribution of diffusible ions.
  • This Donnan Equilibrium, relying on passive diffusion, can be demonstrated by dialysis.
  • The equilibrium that occurs over a membrane,
  • If something can’t be moved, all the diffusible ions will continue to move until the osmotic pressure is equal.
  • Unequal distribution of diffusible ions.
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10
Q

Mention how the ionic composition of seawater and some invertebrate body fluids vary between a few example organisms.

A
  • Jellyfish map very closely to water – slightly less sulfate
  • Crab – actively regulating against the external environment
  • Nephrops – low magnesium. Magnesium effects nerve transmission, and fast impulses needed for escape mechanisms.
  • Squid – low sulfate, which is a heavy ion. Removing it increase its buoyancy.
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11
Q

Give an example of the benefit of reducing heavy ions.

A

Reducing sulphate ion concentration aids buoyancy in squid and jellyfish (work by Eric Denton FRS at the MBA, Plymouth)

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12
Q

Metion baltic sea starfish.

A
  • Echinoderms are stenohaline marine
  • North Sea starfish have a salinity tolerance of ~20 they have reasonable heat tolerance and breed successfully once a year
  • Baltic Sea starfish have a salinity tolerance of ~8.
    • They have a soft integument;
    • Increased water content; poor heat tolerance, reduced metabolism and do not breed.
    • Individuals are recruited from N Sea populations.
    • Do not breed, entirely depndant on supply from north sea.
  • Give up tolerance to temperature and to breed.
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13
Q

Mention osmoconformity in sipunculids

A

The peanut worm Themiste

This acts as a simple osmometer in dilute seawater the animal swells

  • Water enters passively in dilute media
  • After about 10h they reach a new stable, larger volume
  • The worm shrinks again back to its original volume on return to normal seawater

​

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14
Q

Why can some organisms control the amount it swells, but looses their ability to recover quickly afterwards?

A
  • In Golfingia, some amino acid loss reduces the degree of hydration in dilute seawater
    • There is no recovery of volume
  • In Dendrostomum salt loss via the gut and nephridia allows limited volume recovery in dilute seawater
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15
Q

Describe the difference between an osmoconformer and an osmoregulator on a graph.

A
  • Average seawater salinity ~34.5
  • Chlorinity of 18 (18ppt)
  • Osmolality of ~1000 mOsmol.kg-1
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16
Q

What can be some examples of causes of osmoregulation failure ( example of the lug worm (Hediste diversicolor).

A
  • Reduces permeability to salts & H2O in dilute media
  • Exhibits increased 02 uptake in dilute media –(as muscles resist stretching when the animal swells)
  • In low [02] osmoregulation fails
  • In the presence of CN- osmoregulation fails
  • In absence of Ca2+ osmoregulation fails
  • In seawater from 100-75% Na+ uptake is passive
  • Below 75% Na+ uptake is active
  • In seawater from 100-50% Cl- uptake is passive
  • Below 50% Cl- uptake is active
  • Low temperature also exerts an effect and sets the Northern geographical limit for the species
17
Q

What can allow for burrowing organsims to be buffered against changes in slalinity?

A
  • Burrowing organisms in estuaries are ‘buffered’ from salinity variation
  • Where you live – important can act as buffer
  • Below 8 cm no variability occurs in salinity
18
Q

What are the osmoregulatory abilities of Cephalopods?

A
  • Cephalopods are very stenohaline – strictly marine.
  • They do not have osmoregulatory ability but do show ionic regulation.
  • Shell-less gastropods like sea slugs are osmoconformers that are also stenohaline.
  • Aplysia shows limited regulation in 95% seawater but 80% seawater kills it!
19
Q

What are the osmoregulatory abilities of Molluscs?

A
  • Mussels are euryhaline and can tolerate 50% seawater.
  • Similarly, clams and oysters can tolerate reduced salinity by closing the shell valves for several days.
  • Reduces predation from starfish & dogwhelks.
  • Mud snails, Hydrobia ulvae, are less active in low salinity.
  • Haemolymph (blood) concentration alters slowly in inactive snails and rapidly in active snails.
20
Q

Acclimation to reduced salinity

A
  • In reduced salinity, Mytilus loses amino acids and the nitrogenous base taurine
  • This reduces salt loss
  • Acclimation is measured by ciliary activity which is a measure of mussel filtration (feeding)
  • Mussels can acclimate to reduced salinity but this process takes about 30 days
  • Acclimation – 1 variable
  • Animals will acclimate over time to a new salinity regime.
  • The North Sea, and exposed to what you would expect in the Baltic
  • Over time after exposed (30 days) the mussels perform
  • Capacity in the genotype/phenotype to adapt to changes in salinity.
21
Q

‘The lugworm Arenicola marina: A model of physiological adaptation to life in intertidal sediments’

Zebe and Schiedek 1996

wider reading - osmoregulation in Lugworm.

A

Osmoregulation

  • The lugworm is an osmoconformer so when the salinity of the ambient water changes, this induces corresponding changes of the cells.
  • Osmoregulation in the lugworm is accomplished by two distinct and independent mechanisms: one extracellular and one intracellular.
  • Extracellular volume regulation is probably based on a variation of the rate of urine production.
  • Intracellular volume regulation is affected by changing amino acid concentrations, glycine and alanine in particular, in the cytoplasm.
  • After heavy rains, during low tide, lugworms can start swelling and subsequently reduce their volume. In these cases, the amino acid concentration in the body-wall did not change, as this is likely to happen over long -term (i.e. seasonal) salinity changes.
22
Q

Give examples of 4 different types of regulators.

A
  • Carcinus (Shore Crab) - a hyper-regulator - euryhaline
  • Uca - (Fiddler Crab) a hyper-hypo-regulator - warmer tropical environments
    • Mudflats – an osmotic imbalance
    • Can switch hyper/hypo. As the tide gets fresher it will maintain its internal body fluids – like carcinus.
  • Eriocheir - (Chinese mitten crab a strong hyper-regulator
    • Native to SE Asia, very successful invasive species – they are able to regulate
    • Tends to conform, but in really fresh systems is can regulate efficiently
  • Artemia - (Brine Shrimp) - A strong hypo-regulator
    • Range of different responses within one taxonomic group.
23
Q

The shore (green) crab Carcinus maenas

A
  • The shore crab hyper-regulates when in salinities below ~25
  • (c.75% seawater)
  • Living in estuaries, the shore crab osmoconforms at higher salinities and therefore probably needs only to osmoregulate during the peak low tide period
  • This reduces the overall energy expenditure associated with regulation
24
Q

The fiddler crab Uca pugilator

A
  • Uca forages over the surface of exposed estuarine sediment at low tide.
  • It lives in burrows which give it some protection from temperature and salinity variation.
  • Uca hyper-regulates at lower salinities (<~25) and hypo-regulates at higher salinities (>~25).
25
Q

Chinese mitten crab – Eriocheir sinensis

A
  • The Chinese mitten crab has a complex life cycle (catadromous), growing to the adult in freshwater and returning to the estuaries to breed
  • In freshwater and salinities below ~12 (i.e. ~30 % seawater) it hyper-regulates.
  • Early life stages are not able to hyper-regulate and survive in freshwater.
  • This ability is only acquired in the juvenile stage.
26
Q

What are some problems faced by hyper-regulators?

A

(when haemolymph is hyper-osmotic to the external medium)

  • A tendency for water to enter to achieve osmotic equilibrium
  • Solutes tend to be lost
    • –because the internal concentration is higher than the external concentration
    • –water must be excreted and this carries with it some salts
  • These problems can be overcome by:
    • Permeability reduction - – change the composition of the exoskeleton – how porous is it?
    • Active uptake of ions - over gill area
    • Excretion of a dilute urine
27
Q

Mechanisms of permeability reduction

A

•Changes in the boundary tissue structure

•

–increase in phospholipid content of gills as seen for example in Eriocheir sinensis

•

•Changes in the haemolymph-medium interaction

–

–Changes in blood flow rate through gills

–Shunt pathways in the gills

–Changes in ventilation rate or heart rate

–Changes in the water flow over the gills

28
Q

Pathways of salt and water passage in hypo-regulators

A

(Homer-Smith, 1930 - for marine teleosts)

a)Passive diffusion on water is offset by drinking the external medium

●

b)Water absorbed by the gut carries with it a salt burden

●

c)Urine is isosmotic or slightly hyper-osmotic to the external medium

●

d)Net salt extrusion occurs at the gills

29
Q
A

MST2102 (27 decks)

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