According to the School of Nursing and Academic Division of Midwifery at the University of Nottingham, hydrostatic pressure is a type of pressure that is exerted by the blood onto the capillary walls in humans. As blood moves through the capillaries, the hydrostatic pressure drives the blood out of the capillary into the interstitial space.
Capillaries and tissues can exhibit a hydrostatic pressure, according to Cardiovascular Physiology Concepts from Dr. Richard E. Klabunde. Capillary hydrostatic pressure is responsible for the movement of blood and solutes into the interstitial space. Tissue hydrostatic pressure is responsible for filtering solutes out of the tissues into the tissue interstitial space. Both types of hydrostatic pressure are dependent on blood and fluid volumes in the body.
Dr. Klabunde states that in capillaries, the hydrostatic pressure is higher at the arteriolar end of the capillaries and lower at the venular end. This change is pressure allows a gradient to form so that solutes can be filtered in and out of the capillary. In tissues, a similar change in pressure is developed by the compliance of the tissue interstitial and by the volume of the interstitial fluid. Other types of pressure that are important for filtration of the capillaries and the tissues include capillary plasma oncotic pressure and tissue oncotic pressure.