I can't wrap my head around the idea of oncotic pressure and osmolarity, logically.
I imagine a blood vessel. It is filled with proteins, like a ton of proteins and solutes. So this means, according to oncotic pressure and osmolarity, that water will diffuse into this blood vessel.
I can't understand that. If I have a glass full of water, and I drop a bunch of rocks into the water (my proteins) the water will flow out of the glass. It will exert a force, a very basic force of buoyancy, that will lead water out of the glass.
How exactly is oncotic pressure generated?