What is Blood Coagulation?

Madeleine A.

Blood coagulation refers to the process that causes the blood to clot. This process also helps in preventing excessive bleeding when arteries or veins are broken or pierced. Generally, blood coagulation prevents the body's blood supply from escaping through punctures, cuts, or trauma to the blood vessels. In addition, all needed components that are necessary for blood clotting are found in human blood. The coagulation process is usually activated by traumatized tissue, and involves enzymes and proteins interacting on the surface of membranes.

A diagram showing the composition of blood, including platelet cells, which are important for coagulation.
A diagram showing the composition of blood, including platelet cells, which are important for coagulation.

Typically, blood coagulation involves many components, which are referred to as blood coagulation factors. In addition, complex chemical reactions also take place. When blood vessels become injured, the platelets of the affected area clump, or stick together, while adhering to edges of the injury, starting the coagulation process. Platelets are a blood component made up of cell fragments that contain clotting factors. The platelets release messengers to the bloodstream that constrict blood vessels to lessen bleeding and vessel damage.

Blood coagulates around the site of an injury.
Blood coagulates around the site of an injury.

Blood clotting when blood vessels are injured is very important. Without the blood coagulation process, a puncture wound, cut, or abrasion — even a minor one — would continuously bleed, possibly leading to loss of life. Deficiencies in clotting factors can cause hemorrhaging after surgical procedures or injury. In conditions such as hemophilia, the coagulation deficit is related to inherited defects. In other coagulation abnormalities, these deficiencies may be the result of acquired conditions such as Vitamin K deficiencies.

Hemophilia occurs when the blood is unable to clot effectively. This medical condition is caused by a recessive trait that is sex-linked. This means that males are the only sex affected by hemophilia, however, females can be carriers of the genetic defect as well, and pass it down to their children. Typically, symptoms of hemophilia include easy bruising, bleeding without cause or spontaneous bleeding and bleeding into the joints. In addition, urinary bleeding, bloody stools, and prolong bleeding from minor cuts can also be present.

Sometimes, conditions such as thrombocytopenia can affect blood coagulation. This condition results in a very low number of blood platelets. Platelets play an important role in blood coagulation or clotting, and when values are abnormally low, medical intervention is necessary to prevent excessive bleeding. Sometimes certain medications can affect blood coagulation. These include anti-coagulants such as Coumadin®, and even aspirin. These drugs are used for thinning the blood and preventing clots in those at risk for heart attack and stroke.

The platelets involved in clotting are just one component of blood.
The platelets involved in clotting are just one component of blood.

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Discussion Comments


@robbie21 - I was wondering about that, too! All I can find is that the water stops a blog (fibrin) from forming and that contact with air (meaning oxygen, I assume) is necessary for a clot to form. I guess the coagulation pathways just can't get started if the wound is exposed to water. I hope someone more knowledgeable can help us out.


So why won't blood clot underwater? I always notice that if I nick myself shaving my legs, it won't clot until after I get out of the tub (which is annoying because then it's hard to dry off without getting blood on the towel). And once I had a bad blood donation experience and the draw site opened back up in the shower and I bled all over the place. That was fun.

For the record, I have donated blood at least a dozen times and had only one bad experience. Not nearly enough to keep me from going back!

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