Assume you have a U-tube with a semipermeable capillary membrane made of simple squamous epithelium separating the solutions on either side. Blood will be on the left side of the tube, and watery extracellular fluid (ECF) will be on the right side of the tube. Predict what will occur to the levels of fluids by hydrostatic pressure, the pressure of watery fluid pushing on a boundary.

The pressure exerted by a fluid in a confined container (U-tube) at equilibrium, at a given point within the fluid is called its Hydrostatic pressure. Thus both the the blood on the right and ECF on the left are at equilibrium.

Generally the molecules in a fluid usually exert a continuous force on the walls of the surrounding container.This force(hydrostatic pressure) increases downwards to the base of the confinements(U- tube) . Due to force exerted by the weights of the fluids downwards by gravity.

Therefore, if blood at equilibrium, is disturbed by exerting force on it in the U-tube ,through a pump pushing down, then the pressure effect will be addition of the pump force, and the force of the weight of blood acting downwards in the U-tube. (Since Presurre =Foce/Area)

Consequently, fluids from the plasma of the blood pass through the semi-permeable membrane to increase the volume of the fluid on the left side (ECF).The pressure exerted by the fluid as its pass through the pores of semipermeable capillary membrane is called Hydrostatic pressure.

Thus the levels of fluid(blood) in the right column drops, while the volume of ECF on the left increases.