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 water levels by hydrostatic pressure, the pressure of watery fluid pushing on a boundary.

The net movement of water would be a little bit to the left.

The ECF composition compared to blood composition is quite similar. Blood is composed of plasma (watery extracellular fluid) + cells + platelets. Due to the composition of blood compared to the ECF, blood would be a hypertonic solution. Whenever there is a semipermeable membrane, water will tend to move to the hypertonic side by osmosis.