Hemostasis

Hemostasis (or Haemostasis) refers to a process whereby bleeding is halted in most animals with a closed circulatory system.

History

The first medical description of the clinical and genetic features of haemostasis (concerning haemophilia) was by the so called "father of surgery" Abu al-Qasim al-Zahrawi, called thus for his extended original descriptions of operative techniques and instrumentation. He described, and, a method for stopping bleeding by local pressure and cauterisation.

Hemostasis in physiology

Hemostasis can refer to the physiologic process whereby bleeding is halted, thus protecting the integrity of the vascular system after tissue injury. It is responsible for minimizing blood loss. It is commonly referred to as stoppage of bleeding, however, coagulation is only one type of hemostatic process.

The haemostatic mechanisms have several important function:

1. Maintain blood in a fluid state while circulating within the vascular system
2. Arrests bleeding at the site of injury by formation of haemostatic plug
3. Ensure the removal of the haemostatic plug when healing is complete

The components of normal haemostasis include: Blood vessels, platelets, plasma coagulation factors and their inhibitors and the fibrinolytic system.

When a blood vessel is wounded, 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).

Disorders of Hemostasis

Disorders of hemostasis can be roughly divided into:

• Platelet disorders, such as idiopathic thrombocytopenic purpura, and
• Disorders of coagulation, such as hemophilia and thrombophilia.

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 bloodfeeding; 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.

External Links

Hemostasis slides from McGraw-Hill

Bibliography

• Hakim, Naday S. (2007). Haemostasis in Surgery. Imperial College Press. ISBN 1860946917. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)