How blood clots

Blood clotting in health – the normal process

If you cut yourself, there are two main ways in which blood clots to plug the hole.  First come platelets.  These are tiny cell fragments which are usually present in large numbers in blood.  Platelets recognise damaged tissue: if they see it, they latch on, and then recruit more and more platelets, all sticking together until they form a plug, filling the hole.
Next, the coagulation cascade swings into action.  The coagulation cascade is made up of 13 coagulant molecules, known as “clotting factors”, which circulate in the blood in an inactive state.  Tissue injury activates the first clotting factor in the sequence; this then activates the next one down the line, and so on, until the last one, factor 1 (also called fibrinogen), is converted to fibrin.  Fibrin links together in a tough meshwork which helps to hold the platelets together, and stabilise the clot.  Remember the last time you picked a scab?  That was a clot made of platelets and fibrin.  
The animation is somewhat technical but shows very nicely the complexity of the systems at play.


Other links
 The coagulation system- an animation from John Hopkins Medical School

Written by

Matthew Rogers is a Haematology Spr


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