The Clotting Process

When the skin is penetrated or simply cut, some processes begin to seal the injury site, thereby preventing blood loss. Haemostasis is the process is that the body has to prevent blood loss, it has three stages, vascular, platelet and coagulation phases.

Vascular Phase.

  • When the blood vessels are cut the smooth muscles of the blood vessels contract in the area of the damage. The aim of vascular spasms is to reduce the flow of blood to the area by decreasing the diameter. The cells lining the inside of the blood vessels also contract to expose the base lamina and the underlying collagen to blood cells. The endothelial wall becomes sticky so that the opposing walls can stick together and stop blood flow. The endothelium also releases hormones and growth factors which causes vascular spasms and induces Mitosis in the endothelial cells.

Platelet Phase

  • Thrombocytes stick to the collagen and the basal lamina, and the number of sticky platelets increase, they start to stick to each other forming a platelet plug that can close off the hole of the vessel. Platelet aggregation happens very fast usually 15 seconds after the damage. The platelets are activated as they arrive at the site and release a number of factors, such as thromboxane A2 and serotonin ( vascular spasm). They release clotting factors PDGF for blood vessel repair and ADP for stimulation and aggregation.  They also release ions for aggregation and clotting, all this happen as a positive feedback mechanism to produce a plug and ultimately a clot.
  • If the clotting process is unchecked it will continue to happen, but thankfully, we have prostaglandins that will stop the aggregation process. Here also have inhibitors from the white blood cells as well as plasma enzymes that break down the ADP.
  • About 30 seconds after injury, the coagulation phase begins. Although a complex process the ultimate aim of the coagulation phase is to covert the circulating fibrinogen into fibrin strands, that forms a mesh over the plug. This traps the passing RBC and platelets to form a clot.

Intrinsic and Extrinsic clotting pathway. 

  • Extrinsic is initiated in the blood vessel wall by tissue factor while intrinsic is in the bloodstream when factors XII contacts collagen fibres.  The two converge in the common pathway when enzymes from either pathway activate X. This forms prothrombinase which is converted into prothrombin and then to thrombin, converting fibrinogen to fibrin.


Thrombocytopenia – This is a condition that is characterised by abnormally low levels of platelets. If the numbers of platelets fall below 50,000, this is a medical emergency, the normal range is between 150,000 to 450,000 platelets per microliter of blood. Thrombocytopenia often occurs as a result of a separate disorder such as leukaemia or immune system related conditions. Or it can be from taking certain types of medication have been known to reduce the number of platelets.

Signs and Symptoms include:

  • Easy or excessive bruising (purpura)
  • Superficial bleeding into the skin that appears as a rash of pinpoint-sized reddish-purple spots (petechiae), usually on the lower legs
  • Prolonged bleeding from cuts
  • Bleeding from your gums or nose
  • Blood in urine or stools
  • Unusually heavy menstrual flows
  • Fatigue
  • Enlarged spleen
  • Jaundice

Giant platelet syndrome (Bernard-Soulier syndrome)

  • This condition happens when the platelets lack the ability to stick adequately to the injured blood vessels walls, as a result of this there is abnormal bleeding. The condition usually presents in newborn, infancy or early childhood with bruizes, nose bleeds and gum bleeding .later problems may occur with anything that induces bleeding such as menstruation, trauma, surgery or stomach ulcers.
  • This disease is inherited, both parents must carry a gene the syndrome and then transmit the syndrome to the child. There is no specific treatment for giant platelet syndrome, bleeding episodes may require transfusion.
  • The abnormal platelets in the syndrome are usually larger than normal platelets. However, this is not the only condition with larger platelets, specific platelet function test, as well as glycoproteins, are required to determine the diagnosis.

Gray platelet syndrome

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This is a rare disorder, about 60 cases have been reported worldwide,  individuals with the disorder tend to bruise easily and have increased risk of nosebleed, or extended bleeding after surgery. They may also experience abnormally heavy bleeding after dental work, or minor trauma.  Women with the condition experience irregular, heavy periods. These bleeding problems are usually mild to moderate, but sometimes they can be life-threatening.

A characteristic feature of the condition is myelofibrosis which is build up of scar tissue in the bone marrow, the scaring associated with myelofibrosis damages the marrow preventing it from making adequate blood cells. This causes other organs, more specifically the spleen, to start producing more blood cells to compensate, this process may lead to an enlarged sleep.


Smith, S. A., Travers, R. J., & Morrissey, J. H. (2015). How it all starts: Initiation of the clotting cascade. Critical reviews in biochemistry and molecular biology50(4), 326-336.

Laurino, M., Menara, T., Stella, A., Betta, M., & Landi, A. (2015, August). Procoagulant control strategies for the human blood clotting process. In Engineering in Medicine and Biology Society (EMBC), 2015 37th Annual International Conference of the IEEE (pp. 4439-4442). IEEE.

This paper is purely for study purposes, it should not be used as a diagnostic tool. Seek medical help if you suspect any of these conditions above. 


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