Osmo and ion regulation Flashcards
Explain the balance concept
In order for balance to be maintained the input of substances but be equal to the output by means of excretion or metabolic consumption. This concept is important in order to maintain homeostasis
outline the distribution of animal body H2O in the various fluid compartments
Body water is distributed between intra/extracellular compartments
- plasma = 90%
- soft tissues e.g. skin/muscles = 70-80%
- shells/skeleton= 20%
- fat/ external coverings e.g. hair = 10%
The major fluid compartments comprised of intracellular and extracellular fluids
ICF= 2/3 of water in vertebrates/insects and 1/3-1/2 in molluscs
EFC= remaining fluid, divided into plasma and interstitial fluid
compare the ionic composition of plasma, interstitial fluid and intracellular fluid
Na+ and K+ differs between intra and extracellular fluids. Na+ is the primary ECF cation and K+ is the primary ICF cation.
- Majority of ECF and ICF ions are balanced electrically.
- ICF the K+ is partnered with PO4-
- ECF the Na+ is partnered with Cl- anion
define osmosis
the movement of a solvent (water) passively across a semipermeable membrane down the water potential gradient
what is the difference between tonicity and osmolarity
osmolarity= the concentration of all particles in a solution (osmols/litre)
tonicity= solute concentration that directly affects water movement by osmosis the ability for an extracellular solution to make water move into or out of cells by osmosis
what are the three types of tonicity
1) isotonic = no net movement of water so no change in cell volume
2) hypotonic = water diffuses into the cell causing them to swell
3) hypertonic = water diffuses out of the cells causing them to shrink
Describe the types of osmotic challenges faced by animals
1) Differences between ICF and ECF
- potential swelling from unequal Na+ distribution on ECF and ICF. Na+ leaking into cells raises solute conc and thus elevates osmotic pressure causing water to enter the cell, mechanisms to correct this = Na+/K+ ATPase pump
2) ingestion and excretion
- intake of water and solutes through digestive tract may not be of the correct amounts for the body, while excretion of waste products often requires water
3) external environment
- salinity of environment, marine organisms must prevent dehydration and limit salt influx in high salinity while freshwater do opposite.
4) osmoregulation
- control of salt and water balance
compare osmoconformers and osmoregulators in general terms
conformer= body fluid and cellular osmolarity is generally similar to that of the external environment
regulator= body fluid osmolarity is homeostatically regulated different to that of the external environment
- hyper-osmoregulator = body fluid>external
- hypo-osmoregulator = body fluid< external
what are the osmoregulatory problems and adaptations of freshwater species
fresh water = water gain and salt loss = issue
- active uptake of ions = uses ATP in transport epithelia to move ions from enviro into body
- hypotonic fluid excretion= to combat excess water gain they remove it by excreting a fluid that is hypo-osmotic to body fluids
- low permeability of skin= to reduce efflux of solutes and influx of water they reduce permeability of outer body surface
- lower internal osmolarities= to reduce water influx solute concentrations, primarily in less NaCl in the ECF and small amounts of amino acids osmolytes in the ICF
compare stenohaline and euryhaline animals
Eurohaline= tolerates a large range of salinities e.g. fresh and sea water
stenohaline= only tolerates a narrow range of salinities
what are the osmoregulatory problems and adaptations of salt water/ marine species
Problem= water loss and salt gain
adaptations=
- low urine flow rates
- drink seawater to replace lost volume, digestive tract epithelium can restrict influx of some ions but Na+ must be imported allowing water to follow
- active excretion of salt via the gills = special gill epithelia contain chloride cells to actively transport NaCl out with little water movement
- don’t reduce the permeability of their skin
what are the osmoregulatory problems and adaptations of species which alternate between modes of osmotic adaptation e.g. salmon
fresh water to saltwater modifications
- acclimatation induces by growth hormone and cortisol which alter gill epithelial cells triggering growth of seawater chloride cells
- apical proton pump down regulated
- increased basolateral Na+/K+ ATPase activity so removal of excess salt increases
- increased NaCl secretion
saltwater to freshwater modifications
- reduced external NaCl
- paracellular gaps between ionocytes (mitochondrial rich cells) and accessory cells close
- increase prolactin causes changes in gills with fresh water chloride cells
- reduced basolateral Na+/K+ ATPase activity so less removal of excess salt
- upregulation of apical proton pump
- increased NaCl uptake
what are the osmoregulatory problems and adaptations of terrestrial species
both water and salt are a limiting factor
- marine birds and reptiles drink seawater ad secret salt into a salt gland
- marine mammals don’t drink seawater therefore minimising water loss
- terrestrial animals lose water through lungs and skin so salt and water input is regulated via diet and output is regulated via urine and faeces (kidney function)
outline the process of active salt uptake in fresh water teleosts
Acid secreting cell
1) Na+/K+ ATPase lowers cellular Na+
2) H+ ATPase creates a local membrane potential driving Na+ intake
Base secreting cell
1) Cl- uptake by apical HCO3- exchange
2) Cl- enters blood against conc gradient by multiple mechanisms
outline marine teleosts active salt excretion process
1) Na+/K+ ATPase lowers cellular Na+ and increases basolateral Na+
2) Na+ gradient drives Cl- entry via Na+/K+/cl- cotransporters
3) Cl- excreted via apical channels create TEP
4) Na+ excreted by passive paracellular diffusion due to electrochemical gradient (TEP and Na+ gradient )
5) K+ ions must recycle
