What role does albumin have in the osmotic function across the capillaries?
A. Osmosis is the passive movement of water from an area high in water concentration, across a semi-permeable membrane, to an area low in water concentration. This movement achieves an equal amount of water on either side of the membrane. The blood contains a large number of plasma proteins with albumin constituting roughly 60% of it and thus there is less water content in the blood. This creates a concentration gradient between the blood and the fluid in the surrounding tissue. These proteins pull water into that compartment, as the force of osmosis tries to equalise the amount of water in blood and in the interstitial fluid and this pulling power is called oncotic pressure. Strictly speaking, all the dissolved compounds in blood exert an osmotic pressure. A part of this total osmotic pressure is due to the presence of large protein molecules and is called as the colloidal osmotic pressure, or oncotic pressure. Normally, when oncotic pressure is measured, it is measured across a semi-
