Fluid Compartments and Solutes Flashcards
which cation is most abundant intracellularly?
K+
which cation is most abundant in the plasma?
Na+
which anion is most abundant in the plasma?
Cl-
which anion is most abundant intracellularly?
organic phosphates
pH difference?
more acidic intracellularly (7.1 vs 7.4) accounts for a two-fold difference in protons
diffusion?
spontaneous movement of solute down a concentration gradient until solute molecules reach an equilibrium
osmosis?
movement of water down its conc gradient - i.e. water moves towards an area of higher osmolarity
calculating osmolarity?
take concentration of substance (mmol) and multiply by the number of ions in substance
e.g. in NaCl, you’d multiply conc by 2
in situation where membrane is permeable to both water and the solute?
no net change in cell volume
if membrane is permeable to water and solute A but not B?
cell is swollen at equilibrium
if membrane is permeable to H2O but not to solute A?
after equilibrium cell is swollen and might rupture
what do the 3 examples show us?
despite 3 same initial states (Osmi>Osmo) there are 3 different end outcomes
therefore osmolarity isn’t a reliable indicator of effects of solutions on cell volume, tonicity is much more reliable
tonicity?
strength of solution as it affects final cell volume
depends on BOTH cell membrane permeability and solution composition
hypertonic, hypotonic, isotonic
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why doesn’t cell burst if solute concentrations are much higher in cells compared to plasma?
due to presence of Na+K+ATPase
it effectively is impermeable to Na+ because any Na+ that diffuses down its concentration gradient is pumped back out of the cell (i.e. no net movement of Na+ across plasma membrane)
methods of solute movement across membranes?
gases/hydrophobic molecules can diffuse across lipid bilayer
other molecules require membrane proteins
this can be both active (require ATP) and passive (going down electrochemical gradient)
tissue preservation?
organs/tissues that need to be transported to recipient are perfused with cold solutions to reduce deterioration via hypothermia.
what happens with sodium-potassium pump when body is too cold?
Na+K+/ATPase stops functioning below 15 degrees and with no circulation there is no O2 and therefore little ATP to fuel pump
Na+ will therefore enter cell alongside Cl- and water as K+ exits, this will lead to cell swelling –> cell death
UW?
University of Wisconsin solution
used to perfuse organ prior to transplantation
protects it from the sodium potassium pump causing problems (cell swelling)
3 main factors
No Na+/Cl- so no influx
It has extracellular impermeant solutes
it has a macromolecular colloid (starch)
which two pressures determine the solute and fluid movement across a vesssel wall?
Colloid osmotic pressure (higher conc of plasma proteins in capillary than outside)
Hydrostatic pressure inside vessel due to blood flow through vessel
normal conditions for a capillary?
slightly greater hydrostatic pressure than COP, net leakage from capillary
oedema?
due to abnormal balance between COP and hydrostatic pressure, causes fluid accumulation in tissues
common cause is increase in permeability of capillary walls due to leaky capillaries (as proteins are lost through increase in pore size which reduces COP so more fluids are readily pushed out from capillary)
