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Asking from the blood barrier angle. The wikipedia states that glucose, urea, and $\ce{Na/K}$ count. Can there be any other factors, like $\mathrm{pH}$, temperature, hydraulic pressure on the cell walls? Why do minerals not play a role? Because there are only traces of them?

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  • $\begingroup$ I'm a little confused about your question. Do Na/K not count as "minerals"? And no, "minerals" are not generally present as traces in plasma (some may be, depending on what you mean by trace and by "mineral"). $\endgroup$ – Buck Thorn Aug 3 at 20:19
  • $\begingroup$ Do you mean "do any other factors, like pH, temperature, and hydraulic pressure on the cell walls, affect the osmotic pressure?"? $\endgroup$ – Buck Thorn Aug 3 at 21:07
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    $\begingroup$ Beware dangling participles... dictionary.com/browse/dangling-participle $\endgroup$ – Buck Thorn Aug 3 at 21:08
  • $\begingroup$ en.wikipedia.org/wiki/Blood_plasma#Composition $\endgroup$ – Buck Thorn Aug 4 at 10:49
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Osmotic flow is the movement of a substance (typically water), across a semi-permeable membrane, from the side on which the chemical potential of the substance (water) is higher to the side on which it is lower. I.e., just as temperature provides a gradient for the flow of thermal energy, chemical potential provides a gradient for the flow of matter.

Thus anything that affects the chemical potential of water will affect osmotic flow. This includes dissolved solutes, pH (which of course comes from a particular dissolved solute—H$^+$), temperature, and pressure. For instance, increasing the solute concentration decreases water's chemical potential, while increasing the pressure increases it.

Indeed, that's the basis of osmotic pressure—water will flow toward the side with the greater solute concentration (activity) until the pressure on that side increases enough such that the reduction in water's chemical potential due to the presence of the dissolved solutes is exactly negated by the increase in water's chemical potential due to the increased pressure.

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