blood is negatively charged colloid haemoglobin is positively charged colloid they are present together in the body yet they do not coagulate?

blood does not coagulate inside the body due to the presence of heparin inside the body.It is anticoagulant and has highest negative charge density.Heparin is a naturally occurring anticoagulant produced by basophils and mast cells.Heparin acts as an anticoagulant, preventing the formation of clots and extension of existing clots within the blood. While heparin does not break down clots that have already formed , it allows the body's natural clotlysis mechanisms to work normally to break down clots that have formed