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

Explanation:

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.