Fluid Compartments and Solutes

Question 1

which cation is most abundant intracellularly?

Answer 1

K+

Question 2

which cation is most abundant in the plasma?

Answer 2

Na+

Question 3

which anion is most abundant in the plasma?

Answer 3

Cl-

Question 4

which anion is most abundant intracellularly?

Answer 4

organic phosphates

Question 5

pH difference?

Answer 5

more acidic intracellularly (7.1 vs 7.4) accounts for a two-fold difference in protons

Question 6

diffusion?

Answer 6

spontaneous movement of solute down a concentration gradient until solute molecules reach an equilibrium

Question 7

osmosis?

Answer 7

movement of water down its conc gradient - i.e. water moves towards an area of higher osmolarity

Question 8

calculating osmolarity?

Answer 8

take concentration of substance (mmol) and multiply by the number of ions in substance
e.g. in NaCl, you’d multiply conc by 2

Question 9

in situation where membrane is permeable to both water and the solute?

Answer 9

no net change in cell volume

Question 10

if membrane is permeable to water and solute A but not B?

Answer 10

cell is swollen at equilibrium

Question 11

if membrane is permeable to H2O but not to solute A?

Answer 11

after equilibrium cell is swollen and might rupture

Question 12

what do the 3 examples show us?

Answer 12

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

Question 13

tonicity?

Answer 13

strength of solution as it affects final cell volume
depends on BOTH cell membrane permeability and solution composition

Question 14

hypertonic, hypotonic, isotonic

Answer 14

”

Question 15

why doesn’t cell burst if solute concentrations are much higher in cells compared to plasma?

Answer 15

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)

Question 16

methods of solute movement across membranes?

Answer 16

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)

Question 17

tissue preservation?

Answer 17

organs/tissues that need to be transported to recipient are perfused with cold solutions to reduce deterioration via hypothermia.

Question 18

what happens with sodium-potassium pump when body is too cold?

Answer 18

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

Question 19

UW?

Answer 19

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)

Question 20

which two pressures determine the solute and fluid movement across a vesssel wall?

Answer 20

Colloid osmotic pressure (higher conc of plasma proteins in capillary than outside)
Hydrostatic pressure inside vessel due to blood flow through vessel

Question 21

normal conditions for a capillary?

Answer 21

slightly greater hydrostatic pressure than COP, net leakage from capillary

Question 22

oedema?

Answer 22

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)