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Hemostasis is the process that stops bleeding after an injury to blood vessels. It involves two phases, primary and secondary hemostasis, and results in the formation of a blood clot. Thrombosis, the formation of blood clots in a blood vessel, can cause serious health conditions.
Hemostasis is the process by which blood is transformed into a solid state. It is what stops the bleeding after an injury to the blood vessels occurs. Blood vessels are protected by cells that prevent the formation of thrombin, a clotting protein that catalyzes reactions in the bloodstream. When a lesion permeates the cells and reaches the vessels, hemostasis occurs.
There are two phases of hemostasis. During the first primary hemostasis, the vascular muscle temporarily contracts as the cells are disturbed. This contraction slows blood flow and activates or speeds up platelet adhesion. During adhesion, proteins on the surface of each platelet attach to von Willebrand factor, a protein found in blood plasma.
When platelets collect on the surface, they come into contact with collagen, the major protein in humans, and are then activated. These platelets cover the surface and the platelet membrane fibers and receptors grab fibrinogen, a protein found in plasma and synthesized by the liver. When platelets and fibrinogen build up, they form a plug. All of this happens within 20 seconds of the injury.
During secondary hemostasis, the clot stabilizes, but platelet secretions continue the contractions of the vascular muscle. Through the interaction of enzymes, platelet membranes and various coagulation processes, the cork becomes solid. Clotting processes occur in the liver but circulate inactively throughout the body until something called a coagulation cascade begins. During the cascade, a series of steps occurs in which one reaction leads to another until fibrinogen is converted into fibrin, a protein that forms the hemostatic plug or clot on a lesion. Fibrin initially has a reticular consistency, but when platelets and red blood cells combine with a dense grouping of fibers, a blood clot forms.
Hemostasis and thrombosis are closely related, as thrombosis is the formation of blood clots in a blood vessel. Thrombosis can occur in a vein or artery, and the clot itself is called a thrombus, which is Greek for lump or clot. Thrombosis in a vein can cause deep vein thrombosis, a condition that affects blood clotting in the legs. Coronary thrombosis is thrombosis that affects the arteries and can cause a heart attack when a blood clot cuts off the blood supply to the heart. A thrombus can be caused by an injury to a blood vessel, disruption of normal blood flow, inflammation, or atherosclerosis.
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