Hemostasis: Difference between revisions

[[Image:Blood_clotting.jpg|400px|right]]

== Steps of Hemostasis ==

Hemostasis is composed of four major processes in a set order. '''Vascular constriction''' is the first step of hemostasis. It stops the blood flow to the area that is injured. When a person gets injured, Vascular constriction occurs to prevent excessive bleeding. After vascular constriction, thrombin activates platelets and they aggregate at the site of the injury, and loose platelet fibrogen. After thrombin activates platelets, the clot forms and entraps the plug. '''White thrombus''' is present when the plug contains only platelets; a '''red thrombus''' is present when red blood cells are present. Finally, the process proceed the last step, [[tissue repair]]. the clot is dissolved in normal blood flow. The clot is dissolved through the action of plasmin. <ref>[http://themedicalbiochemistrypage.org/blood-coagulation.html The Medical Biochemistry] Michael W. King, Ph.D, IU School of Medicine, February 24, 2011.</ref>

When a person's blood vessels are damaged, hemostasis begins its three steps to arrest bleeding. The three steps are a '''vascular constriction''', a '''platelet plug''', and a '''coagulation'''. The explanation of a vascular spasm and a platelet plug is followed. However, the explanation of coagulation will be located on the next section.

• A vascular constriction is a constriction of the damaged blood vessel which occurs at the site of injury. Vasoconstriction is initiated by the smooth muscle of the blood vessel in response to the injury and by nerve signals from pain receptors.

[[Image:Blood_coagulation.png|thumb|250px|Biochemical blood coagulation cascade.]]

Coagulation (or blood clotting) is the most complex stage of hemostasis. There are three steps in coagulation: Prothrombinase, thrombin, and fibrin. '''Prothrombinase''' is an enzyme that is produced when blood vessels or some other tissues are damaged. Prothrombinase is also called 'coagulation factor II' (F2). Prothrombinase occurs in blood plasma. Prothrombin is produced by the liver and the liver puts prothrombinase into the bloodstream. The next step is '''thrombin'''; another enzyme that prothrombinase converts prothrombin. After the second step, thrombin, the last step occurs when thrombin interacts with '''fibrinogen'''. Fibrinogen is one of the proteins in blood plasma. Fibrinogen is converted into fibrin when thrombin interacts with fibrinogen.<ref name=wile327>Wile, Jay L., and Shannon, Marilyn M. ''The Human Body: Fearfully and Wonderfully Made!''. Cincinnati: Apologia Educational Ministries, Inc., 2001. Print.(P327-328)</ref>.

'''Process'''<br />

A blood clotting consists of a plug of platelets enmeshed in a network of insoluble fibrin molecules. Blood clotting requires calcium ions (Ca²⁺) so the blood do not clot in the bag. This system also requires about a dozen other protein clotting factors. <ref name=Kimball>[http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/Clotting.html Blood Clotting] John W. Kimball, Kimball's Biology, January 11th, 2011.</ref>

'''Control'''<br />

Blood clotting system is controlled by antithrombin III, heparin, protein C, vitamin K, and warfarin (Coumadin). Antithrombin III is a plasma protein (a serpin) prevents the formation of thrombin by binding to prothrombin. Heparin is a mixture of polysaccharides that bind to antithrombin III. Protein C is a protein that sits at the center of the control mechanism system. It excess thrombin binds to cell-surface receptors, called thrombomodulin. Vitamin K is a cofactor needed for the synthesis of protein S. Lastly, warfarin is another name of blood thinner because it is an effective vitamin K antagonist.<ref name=Kimball/>

== References ==

* To see the process of hemostasis with a video, visit the following web address:

http://www.mhhe.com/biosci/esp/2002_general/Esp/folder_structure/tr/m1/s7/trm1s7_3.htm