What is haemostasis?

Haemostasis (also spelled hemostasis) is the process of stopping bleeding. It involves a complex interplay between blood vessels, platelets, and clotting factors in the blood. In hemostasis, blood loss is prevented by the formation of a blood clot (also known as a thrombus) at the site of injury, while ensuring that blood continues to flow freely through other blood vessels.

The hemostatic process can be divided into three main stages:

1. Vasospasm: Immediately after injury, the blood vessels at the site of injury constrict (narrow) in a reflex action called vasospasm. This constriction reduces blood flow to the area, slowing down the rate of bleeding.

2. Platelet plug formation: Platelets are small, colorless blood cells that play a crucial role in hemostasis. They become activated upon injury and adhere to the damaged blood vessel. Activated platelets undergo a process called aggregation, where they clump together and form a platelet plug at the site of bleeding. This plug acts as a temporary seal to prevent further blood loss.

3. Blood coagulation: Blood coagulation, also known as blood clotting, is the process by which blood changes from a liquid to a semi-solid gel-like state, forming a blood clot. This process involves a series of complex biochemical reactions called the coagulation cascade. During coagulation, clotting factors (proteins present in the blood) interact with each other in a stepwise manner, ultimately leading to the conversion of a protein called fibrinogen into insoluble fibrin strands. These fibrin strands form a meshwork that traps platelets and red blood cells, creating a stable blood clot that seals off the damaged blood vessel and promotes healing.

Once the blood clot is formed, it remains in place until the damaged blood vessel is repaired. As the healing process progresses, the blood clot gradually dissolves through a process called fibrinolysis, and normal blood flow is restored.

Hemostasis is crucial for maintaining the integrity of the circulatory system and preventing excessive bleeding in the event of injury. It is a finely tuned process, and disruptions in any of the steps involved can lead to bleeding disorders or excessive clotting.