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the formation of a jellylike substance over the ends or within the walls of a blood vessel, with resultant stoppage of the blood flow; called also coagulation.

Clotting is one of the natural defense mechanisms of the body when injury occurs. A clot will usually form within 5 minutes after a blood vessel wall has been damaged. The exact process of clotting is not known; however, it is believed that the mechanism is initiated by the platelets, which adhere and aggregate as they come in contact with the injured surface. As they aggregate they release serotonin and other substances from their dense granules. Serotonin causes constriction of the blood vessels and reduction of blood flow. Thromboplastin unites with calcium ions and other substances that promote the formation of fibrin. When examined under a microscope, a clot consists of a mesh of fine threads of fibrin in which are embedded erythrocytes and leukocytes and small amounts of fluid (serum).

Twelve factors essential to normal blood clotting have been described; see coagulation factors. At least four platelet factors also exist that have a part in clotting.

It is possible for a clot to form within a blood vessel if the inner wall of the vessel has been roughened by injury or disease. Clots may form in conditions such as arteriosclerosis, varicose veins, and thrombophlebitis. An internal clot that remains at the place where it forms is called a thrombus; the general condition is called thrombosis. If the clot (or pieces of it) breaks loose and flows through the blood vessels, it is called an embolus, and the condition is called embolism.

Clotting of the blood can be hastened by contact with injured tissue, by warming, by adding such coagulants as calcium, or by combination with thromboplastin and thrombin. The process can be retarded by cooling, by dilution, by adding oxalates and citrates, or by administration of substances such as heparin and dicumarol, called anticoagulants.
The clotting process.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.


Process of coagulation; the transformation of blood from a liquid into a semisolid mass.
Medical Dictionary for the Health Professions and Nursing © Farlex 2012


Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005

Patient discussion about clotting

Q. What causes blood clots? My father had a heart attack which was caused by a blood clot. Am I at risk for developing blood clots too? How do I prevent it from happening?

A. I found a website that checks your risks for inheriting your family's illness, including blood clots. They have a test you can do which is called "Free Risk Assessment for Thrombophilia":

Q. How can I prevent blood clots? I am 45 years old and am supposed to go on a business trip overseas. The flight itself is 12 hours long and then I have to continue traveling by bus. Could this cause me to have blood clots? If so, how can I prevent it?

A. Always walk as much as you can on the plane. Also, rotate your ankels in circles. Sometimes try to use your ankels and make the alphabet with them. Have fun..

Q. very dark blood clots @ first sight of period? At first sight of period, instead of normal rosy spotting it's brownish spotting followed by small clots.

A. totally agree with hottie, most likely that will be in normal range of variation. unless you feel some unusual pain, then you need to find medical advice. but it is also suggested for you to go to your ob-gyn doctor for a regular checkup anyway.
stay healthy always..

More discussions about clotting
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References in periodicals archive ?
After clotting had oc-curred, this was mounted above a microscope slide for microscopic inspection.
The objective of this study to measure coagulation time of skim milk by using Mucor miehei rennet at different pHs and temperatures, and determination of optimum milk clotting time with mathematical model depending on experimental data.
A traveler developing a blood clot may need to be tested for inherited clotting disorders and other conditions.
This bleeding disorder lacks some of the protein components of the clotting cascade, often referred to as the glue that helps a clot stick together.
This interaction - between a clotting factor and a cell membrane - has baffled scientists for decades.
Historically, each newly discovered factor within the clotting cascade has been allocated a roman numeral.
"In people with widespread clotting involving the thigh and pelvis, this more aggressive approach should be strongly considered."
Medicare's payment for clotting factor, like other outpatient drugs, is 95 percent of the average wholesale price (AWP), a price established for each drug by its manufacturer.
This project will determine whether blood clotting factor homologues are expressed in fiber type-specific muscle exposed to the atrophy of simulated microgravity.
Blood levels of several proteins associated with inflammation of the blood vessels and blood clotting were measured the morning before the marathon, within four hours after, and the morning after.
THE risk of suffering from fatal blood clotting during a flight, or 'economy class' syndrome, is greater than first thought, a new report claimed today.
* Blood clotting. Many heart attacks or strokes occur when a blood clot gets stuck in a partially clogged artery.