Hemostasis

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Hemostasis refers to the physiologic process whereby bleeding is halted in most animals with a closed circulatory system. Stopped bleeding is commonly referred to, however, as coagulation, but coagulation is only a part of the hemostatic process.

Hemostasis in physiology

When a blood vessel is injured, several steps occur to staunch the flow of blood, namely:

Vasoconstriction constricts the blood vessel, minimizing vessel diameter and slowing bleeding.
Primary hemostasis occurs, wherein platelets, one of the formed elements of the blood, bind to collagen in the exposed walls of the blood vessel to form a hemostatic plug within seconds after an injury.
Secondary hemostasis or coagulation occurs. This involves a complex cascade of coagulation factors, ultimately resulting in the transformation of fibrinogen, a blood protein, into polymerized fibrin, making a clot. This process takes several minutes.
The clot attracts and stimulates the growth of fibroblasts and smooth muscle cells within the vessel wall, and begins the repair process which ultimately results in the dissolution of the clot (fibrinolysis).

Hemostasis may also refer to the complex interaction between vessels, platelets, coagulation factors, coagulation inhibitors and fibrinolytic proteins to maintain the blood within the vascular compartment in a fluid state. The objective of the hemostatic system is to preserve intravascular integrity by achieving a balance between hemorrhage and thrombosis.

Hemostasis can be induced by adenosine diphosphate (ADP) at the site of a mosquito bite to recruit platelets and oppose blood-feeding; however mosquitoes have developed salivary apyrase to degrade ADP to counter this defense.

Hemostasis by Hemostatic Clamps

Hemostasis may refer to the process of manually clamping a blood vessel, usually with hemostatic clamps, in surgery or dissection, to prevent bleeding from that vessel. This also may be done when an abnormal blood vessel forms, as these vessels may have thin walls and be prone to rupturing.

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Overview