HEMOSTASIS When blood vessels are cut or damaged, the loss of blood from the system must be stopped before shock and possible death occur. This is accomplished by solidification of the blood, a process called coagulation or clotting. shock A blood clot consists of a plug of platelets enmeshed in a network of insoluble fibrin molecules.platelets Platelet aggregation and fibrin formation both require the proteolytic enzyme thrombin.

The Clotting Factors Many different blood coagulation factors are present in the body. Each plays a crucial role in the process described above. Some work to increase the activity level of the other factors while some of the factors help set off the chemical cascade which leads to the development of fibrin. Each of the factors has their own levels which should be present in the body. Different deficiency levels are a cause for concern with each of the factors. For example, if one factor is 5% lower than it should be that might be a problem while another factor could be 15% lower and not pose a concern.

Clotting also requires: Calcium ions (which is why blood banks use a chelating agent to bind the calcium in donated blood so the blood will not clot in the bag) about a dozen other protein clotting factors. Most of these circulate in the blood as inactive precursors. They are activated by proteolytic cleavage becoming, in turn, active proteases for other factors in the system.proteases

FactorName_____ I Fibrinogen II Prothrombin III Tissue factor or thromboplastin IV Calcium V Proaccelerin VII Proconvertin VIII Antihemophilic factor A Antihemophilic globulin IX Antihemophilic factor B Plasma thromboplastin component Christmas factor X Stuart-Prower factor XI Hemophilia C Plasma thromboplastin component XII Hageman factor XIII Fibrin stabilizing factor

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Pathways of Coagulation

Tests can be done to determine how effective your body’s ability to handle blood clotting is. These tests look at the different amounts of these blood coagulation factors that are present. When amounts are in sufficient quantities, blood clotting is normal. However, if the levels of some or all of the factors are low this could indicate a serious problem.

Diagnostic Tests Prothrombin Time (disorders in extrinsic system Partial Thromboplastin Time (disorders in the intrinsic system except platelets and Factor XIII) Thrombin Time (fibrinogen) Bleeding Time (platelets)

Reduced levels of the blood coagulation factors needed for hemostasis can be inherited through genetics or can develop thanks to other diseases, including liver disease, some forms of cancer, and even some vitamin deficiencies.

When certain factors are not sufficient, they may need to be replaced through blood transfusions or with drug therapy. These procedures are done either when bleeding is occurring or is likely to occur (prior to surgery, for example).

A deficiency of a clotting factor can lead to uncontrolled bleeding. The deficiency may arise because not enough of the factor is produced or a mutant version of the factor fails to perform properly.

Examples: von Willebrand disease (the most common) hemophilia A for factor 8 deficiency hemophilia B for factor 9 deficiency. hemophilia C for factor 11 deficiency disseminated intravascular coagulation (DIC) widespread formation of thromboses in the microcirculation, mainly within the capillaries. It is a secondary complication of a wide variety of disorders all of which activate in some way the intrinsic coagulation sequence. Paradoxically, the intravascular clotting ultimately produces hemorrhage because of rapid consumption of fibrinogen, platelets, prothrombin, and clotting factors V, VIII and X.

So in a nutshell… First we have an injury… Then we have vasoconstriction… Platelets begin to clump to form a plug… Coagulation factors begin a cascade… Cascade results in a conversion of fibrinogen to fibrin… Fibrin with platelet plug and RBC= CLOT… Clot begins to lyse as final repair is made… And if you’re lucky and you don’t pick the scab you might not even have a scar!

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