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All you need to know about blood clotting

All you need to know about blood clotting

Your body contains 25 trillion red blood cells. That’s roughly one quarter of the cells in your body—and thus a quarter of who you are. When a blood vessel is cut, clotting needs to happen fast to preserve this precious resource.

The importance of speed

Narrowed blood vessel
Image via Everyday Health

Within 15 seconds of cutting yourself, platelets (tiny cell fragments in the blood) clump together to begin to plug the hole (aspirin works by reducing the stickiness of platelets). The injured blood vessel also narrows to reduce blood loss. Blood clotting is generally complete within a matter of minutes.

I witnessed this first hand when administering first aid to a young man after a motorcycle accident. He had severed an artery in his leg and lay in a large pool of blood. Even before I began to compress the wound with a towel, clotting had commenced, reducing the blood flow.

Compare this to the BP oil spill of 2010. It began on April 20 and was not sealed until September 19. Five million barrels of oil spilled out, despite desperate attempts to seal it with mud, golf balls, rubber balls and cement. The human clotting system is awesome in comparison.


The Mayday call

Blood clooting proteins
Image via Chemistry Learning

When you cut a part of your body, signals are sent out (in the form of proteins from the injured tissue and the platelets) to call for help from all corners. The liver responds by releasing a number of different proteins (called clotting factors) that kick-start a chain reaction in the blood, culminating in the formation of a tough mesh of fibres that combines with platelets to form the clot.

Red blood cells, white blood cells and more platelets are trapped within the forming clot, enlarging it until the leak is stopped. Panic over.


Coming out of the shadows

Blood clotting
Image via Healthy New Age

Your liver doesn’t only produce the clotting factors when the emergency call goes out: they are present in your blood at all times in an inactive form, waiting and watching for the moment of injury. Other ingredients important in blood clotting are calcium and Vitamin K. Vitamin K helps the clotting factors to be made in the liver (warfarin interferes with its action); calcium is called to help activate them when the time is right.

An army in peacetime stands ready to respond; your blood contains inactive ingredients silently surveying the scene, on call 24/7.


Controlling the clot

Controlling the clot
Image via YouTube

It’s important that clot formation is controlled and restricted to the site of injury, whilst the rest of our blood continues to circulate freely.

Thankfully, our blood contains several anti-clotting proteins. One such protein is named Protein C (move over Mr T from the A-Team, Protein C is the hero here). It works to perfectly balance the clot building proteins and allow free blood flow around the clot.

Finally, once healing is complete, the entire clot shrinks, dissolves and falls off. Whilst tempting to pick at your scab, it would be better to consider the wonders at work in forming the clot and let the healing process complete.


Helen Cowan completed a PhD in cardiac pharmacology at Oxford in 2002. She is a qualified nurse and has written for the British Journal of Cardiac Nursing, and worked as a columnist in the Nursing TimesRead more from Helen here.

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