The Starling balance defines how fluid pressure pushes plasma out of the capillaries, until it is in an equilibrium with the oncotic pressure. I think one factor tends to be overlooked, differences in fluid pressure in systole and diastole. The filtration during systole reaches an equilibrium with the osmotic potential of the blood, and reabsorption during diastole takes place as the fluid pressure drops below the oncotic pressure, favouring reabsorption until equilibrium is reached again.
