Question

Estimate how much the brain would swell due to osmosis if the concentration of the cerebrospinal fluid fell to 280mm. in other words, find what the new volume of the brain would be once equilibrium was reestablished. assume that (i) the cerebrospinal fluid is constantly replenished, so its solute concentration won't change; (ii) only water is passing across the cell membranes into brain cells (not solutes); and (iii) the volume of the brain is mostly water.

Answer 1

Since the average osmotic pressure of the brain is 300mM and the concentration of the solution is 280mM, that means there is 20mM difference between the brain cells and CSF. This will induce osmosis and cause water to move from the CSF into the brain until the concentration becomes same. Assuming brain volume is 1200ml and the CSF constantly replaced, then the estimation of fluid should be: 20mM/300mM * 1200ml= 80 mlIf it made percent it should be: 80ml / 1200ml= 6.67%