When black night turns red by gunshot and blade, when pressures drop and life starts to fade, doctors are solaced by words which can jade, ALL BLEEDING STOPS! Words truly in gold, bare comfort they hold, patients beg for rescue more bold, so here the story of blood’s clotting be told. Of Platelets and Factors we shall talk, before no corpuscle, nor artery shall we balk, come with us now as we walk, the miracle of dry wounds we shall stalk.
Why does bleeding stop? It is one of the most remarkable events in medicine that a liquid can suddenly become a solid, clotting a laceration, and saving a life. On the other hand, lives can be lost when clots occur when not needed or bleeding erupts from almost no wound at all. Finally, we often prevent disease by altering blood’s clotting.
There are two main parts of this process, which is known as hemostasis: Platelets, and the process of clotting itself, called the Coagulation Cascade. These two parts are made up of a multiple lesser parts and when there is an injury or damage to a blood vessel (capillary, vein or artery) they act like a pyramid of dominos. One fires, then two, then four, in expanding events, that eventually form a clot and seal the blood vessel to stop the bleeding.
Platelets are sticky microscopic particles manufactured in our bone marrow that circulate in our blood. Usually, they just float around, doing little. If a blood vessel is injured, the smooth wall of the vessel becomes rough. This irregular surface attracts platelets, which stick to the damaged site. This is known as adhesion.
Once a few platelets adhere to the damaged site, they attract other platelets that stick to them in a process called aggregation. As the platelets stick together, they trap millions of red blood cells. This forms a plug, which fills the hole. The bleeding begins to stop.
Once the platelet plug is formed, the platelets secrete chemicals. These chemically start the clotting. The process of clotting involves more then a dozen chemicals, called clotting Factors, which, like dominos, activate other chemicals. This results in a series of reactions known as the coagulation pathway or cascade. More and more Factors are activated. The final event is the creation of a chemical known as fibrin that forms a microscopic matrix of fibers. Fibrin causes the whole mix of platelets, red cells and Factors to turn into a gel. That gel, we call a clot. Voila, bleeding stops. All of this can occur in seconds, if the conditions are correct.
What makes this process fascinating is that it explains many medical facts that we all know. Why do they teach Boy Scouts to put pressure on a wound? This stops the flow of blood out of the wound that keeps washing away all the platelets and factors. Why does aspirin make people bruise or why does it stop heart attacks? It stops platelet adhesion. Why do 30 percent of patients with active cancer get blood clots? Cancer makes chemicals that activate clotting Factors. Why do people with hemophilia or Von Willebrand’s disease bleed? They have low levels of clotting factors. Why do we give patients the blood thinner known are Coumadin or warfarin? The medicine stops the body from making certain clotting factors.
All bleeding does indeed stop. Fortunately, most of the time, it stops because of the actions of a remarkable, delicate and complex series of events, which happen nearly instantly and usually flawlessly. A silent guardian giving comfort to both the nighttime surgeon and the little boy with the skinned knee.