Plasma is the liquid component of blood, in which the red blood cells, white blood cells, and platelets are suspended. It constitutes more than half of the blood's volume and consists mostly of water that contains dissolved salts (electrolytes) and proteins.
The major protein in plasma is albumin. Albumin helps keep fluid from leaking out of blood vessels and into tissues, and albumin binds to and carries substances such as hormones and certain drugs.