The Haemostasis Pathway



There are three steps to the haemostasis pathway. One is vascular spasm. Two is platelet plug formation. And three is blood coagulation.

The first is vascular spasm.

Vase constriction of the smooth muscle within the walls of the vessel is the body's first response to bleeding. The vascular spasm response is believed to be triggered by several chemicals called endothelins that are released by vessel lining cells and by pain receptors in response to vessel injury. This phenomenon typically lasts for up to 30 minutes, although it can last for hours.

If the damage to the blood vessel wall is small enough, a platelet plug will be formed to obtain haemostasis.

This is the second response, which refers to when platelets adhere to the damaged endothelium of the vessel, forming a plug. Platelets form part of the components in the blood and a low platelet count is known as thrombocytopenia. If this occurs, the patient will have difficulty forming clots. In contrast, thrombocytosis is a high platelet count and can predispose a person to develop clots.

The last step is at a blood coagulation. In this step, the coagulation cascade is initiated. Here the clotting factors come into play and fibrin is formed, creating a mesh around the plug holding it in place. This is called secondary haemostasis. The plug is now called a thrombus or a clot.

CPD time2m
First Published09 July 2019
Updated09 July 2019
29 June 2025
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