A clotting pathway is a series of reactions inside the body that creates a blood clot to facilitate wound healing. There are two primary pathways which occur in response to different stimuli. Known as the intrinsic and extrinsic pathways, they have been extensively observed and studied in lab settings since the early 20th century. Errors during the coagulation process can occur as a result of congenital conditions, deficiencies, and other interference which may result in bleeding disorders because the patient’s blood cannot clot properly.
The extrinsic clotting pathway starts with a tissue injury, and is also known as the the tissue factor pathway. When bodily tissues are injured, a cascade of reactions begins, involving a series of proteins known as clotting factors that communicate with each other. Each reaction triggers a new reaction until the body successfully forms a clot of a material called fibrin. When the wound is healed, the body uses a technique called fibrinolysis to break up the clot and remove its components so it does not cause complications.
Also known as the contact pathway, the intrinsic coagulation pathway occurs in response to changes in cell structure, such as issues with the walls of the blood vessels. It also requires a series of reactions between clotting factors to create a clot of fibrin which protects the injured area. Once the injury is resolved, the body can break up the fibrin and restore the tissue to its normal condition. Patients are not aware of this clotting pathway, as it occurs inside the body.
While each clotting pathway starts differently, with its own set of factors, they end in the same series of steps. These steps are known as the common clotting pathway, a reference to the fact that no matter what triggers clot formation, eventually it will end with these reactions. Other factors within the cascade ensure it only performs the intended function, without any deviations that might threaten the patient’s health.
Patients can have a congenital shortage of certain clotting factors, seen most famously with hemophilia. In this bleeding disorder, patients lack one of the proteins they need to form blood clots, and they bleed freely when injured. It is possible to supplement with injections of the missing factor to control bleeds. Several different forms of this condition are present in the human population, each involving its own clotting factors.