Platelet Stent video. Computer-generated image. Blood is a specialized bodily fluid that delivers necessary substances to the body's cells such as nutrients and oxygen and transports waste products away from those same cells. Capillaries are the smallest of a body's blood vessels and are part of the microcirculation. Monocytes(shown here as in white) eventually leave the bloodstream to become tissue macrophages which remove dead cell debris as well as attack micro organisms. Thrombus, or blood clot, is the final product of the blood coagulation step in hemostasis. It is achieved via the aggregation of platelets that form a platelet plug, and the activation of the humoral coagulation system (i.e. clotting factors). A thrombus is normal in cases of injury, but pathologic in instances of thrombosis.