Clotting for Life



When we bleed why does it stop?

Blood is under pressure as it flows through your circulatory system and like a broken pipe that leaks water, when you get hurt and injure some of your blood vessels, you bleed.  Your body is able to quickly stop the bleeding by forming a fibrin clot at the injured site.  Without this ability you’d die from either a hemorrhage in your gastrointestinal system or your brain.  But, it's also important to realize that your blood has to flow freely throughout your body so all of your cells can get what they need to work properly, or else you could be disabled or even die.  Your life can be threatened by a heart attack, which takes place when one of the main arteries supplying blood to the heart muscle gets blocked by a clot, or a stroke, when this takes place in the brain.  So, for you to be able to live, it's important that your clotting mechanism turn on only when it's needed and turn off, and stay off, when it's not. 

Your body accomplishes this by having the tissue that lines your blood vessels send out anti-clotting factors which, together with others in the blood (made in the liver), normally prevents clotting.  When injury takes place, this anti-clotting environment is disrupted and with the exposure of your blood to the tissue below the surface of the blood vessel, turns on the clotting mechanism which involves three necessary components.  

First, the muscle surrounding the injured blood vessel contracts to significantly reduce the size of the opening, and with it, blood loss.  Next, the platelets, which normally float freely within your blood, become activated causing them to stick to each other and recruit others to pile on at the injured site to form a soft platelet plug.  In addition, platelets have receptors for fibrinogen, the main clotting factor, which attaches to them when they become activated.  Finally, the normally inactive clotting factors (there are about ten), dissolved in your blood, chemically interact with each other like dominos, in something called the coagulation cascade, ultimately forming a firm fibrin clot.  This stops the bleeding and allows your blood vessel to repair itself over the next few days. 

So that’s why you stop bleeding when you’re injured.   Clinical experience teaches us that to prevent excessive bleeding while allowing for the free flow of blood throughout your circulation, pro and anti-clotting factors strike a delicate balance in that even a slight change in either one can lead to widespread clotting or hemorrhaging.


Three Questions for Mr. Darwin

  1. If muscle contraction around the injured blood vessel, platelet aggregation, activation of the coagulation cascade, and anti-clotting factors are each needed to allow for controlled clotting, how could such a system have developed gradually one step at a time and how did intermediate organisms survive and reproduce without any one of these components?

  2. How does my body know how many platelets, clotting, and anti-clotting factors it needs to make so that it doesn’t die from too many clots or excessive bleeding?

  3. Even beavers know how much and what types of materials to use to patch a hole in their dam, so where did the information come from to teach my body how to form a patch with enough strength to fix my blood vessel when it gets injured?    



 

Also see Dr. Glicksman's Series on

"Beyond Irreducible Complexity"

"Exercise Your Wonder"


Howard Glicksman M. D. graduated from the University of Toronto in 1978. He practiced primary care medicine for almost 25 yrs in Oakville, Ontario and Spring Hill, Florida. He now practices palliative medicine for a Hospice organization in his community. He has a special interest in how the ethos of our culture has been influenced by modern science’s understanding and promotion of what it means to be a human being.

Comments and questions are welcome.

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