When the human skin is broken and a blood vessel severed, the platelets swarm the area of the opening and initiate the foramtion of a blood clot. This is done by activating the substance called thrombin. When the edothelials tear during a skin break, the collagen within the endothelials becomes exposed. Platelets are capable of attaching to the collagen once thrombin has been released and so they form a themporary clot, also called a platelet plug over the open area.
Thrombin is also the enzyme that catayzes the conversion from the protein fibrinogen to fibrin when calcium is present. Fibrin then forms a network beneath the platelet plug that secures it.
Once a platelet has been activated, it continues the coagulation cascade by releasing adenosine-5-diphosphate, ADP and TXA2. These continue to activate other platelets. The original platelet also releases sertonin, phospholipidse, lipoproteins, and additional proteins.
After such a blood clot has been created, it must also be dissolved so that blood flow may resume and heal the injured area. If the blood clot was in response to an injury of the tissue, an extrinsic pathway is used to heal the damage. When a clot has formed due to an injury to the vessel wall without a tissue problem, an intrinsic pathway is used for healing. Regardless of location or type of a clot, proteins that are called clotting factors are used to heal the area and dissolve the clot.
definition of...
Coagulation:
The phase change of a substance, esepecially blood, from a liquid to a solid
"intrinsic"
the pathway that uses only factors which are soluble in plasma
"extrinsic"
the pathway that uses factors that are insoluble in plasma and are therfore found separate from the reactjion itself
www.indstate.edu/.../coagulationcascade
