Description:
-What is blood clotting?
Blood clotting is a process when blood clot rushes to a damaged/broken blood vessel, and solidify in the damaged area, stopping additional blood from flowing out. Blood clot consists of platelets and many fibrin molecules. Thrombin is an enzyme needed for fibrin and platelet formation. Additional requirements are calcium ions and plasma proteins, which act as catalysts, speeding up the process of blood clotting.
-Starting the process:
There are 2 main processes that start the blood clotting: extrinsic pathway and intrinsic pathway. For both pathways, there is a picture below indicating several surface proteins, called tissue factors (TF). Each tissue factor is marked by a number. Damaged cells display tissue factors (TF). In the extrinsic pathway, the TF binds to Factor 7 (F7), forming TF-7. TF-7 has 2 substrates, which are F9 and F10. In the intrinsic pathway, F12 circulates in the blood and activates F11, which activates F9, which activates F10. F10 activates F5, which activates thrombin. Thrombin makes fibrin, and also activates F13. F13 forms covalent bonds between the fibrin molecules, forming 1 part of the clot. In a damaged blood vessel, collagen (component of connective tissue) and extracellular matrix (outer part of cell) are let out. The platelets rush towards the collagen through the Von Willebrand factor, which links the platelets to the collagen. This allows platelets to fill the damaged part of the blood vessel. They release ADP and thromboxane A2, which signal more platelets to rush to the damaged site. They also release tissue factor, and serotonin, which starts the clumping of the platelets, and constricts the blood vessel, thus ending the process of blood clotting.
Relevance:
In term 4, we learned about blood clotting in the circulatory system. We learned about platelets, and how they rush towards a damaged site of a blood vessel. We learned that platelets dry up, sealing the damaged site and prevent additional blood from rushing out of the damaged blood vessel.
Source:
URL: http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/Clotting.html
Author: John W. Kimball
Date of Publication: January 5, 2012
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