Normal plasma volume is about 5% of body weight, or roughly 3500 mL in a 70-kg man. Plasma clots on standing, remaining fluid only if an anticoagulant is added. The plasma proteins consist of albumin, globulin, and fibrinogen fractions. These proteins therefore exe an osmotic force of about 25 mm Hg across the capillary wall that pulls water into the blood. The plasma proteins are also responsible for 15% of the buffering capacity of the blood. Ref: Barrett K.E., Barman S.M., Boitano S., Brooks H.L. (2012). Chapter 31. Blood as a Circulatory Fluid & the Dynamics of Blood & Lymph Flow. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks (Eds), Ganong's Review of Medical Physiology, 24e.