How Does Blood Clot?
How Blood Clots After Injury: Coagulation Process

Heart Health

How The Blood Clots


How Does Blood Clot?
When Is A Blood Clot Dangerous?
Symptoms Of A Dangerous Blood Clot

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What Is Blood?
Circulatory System
How Does Blood Clot?

Terminology: Blood clotting is also called coagulation. Hemostasis is a word for the process where a blood clot forms.

Blood clots form to stop excess blood leaking from your body after you break or cut the surface of your skin. If a blood vessel (a capillary, vein or artery) is damaged (internally or by external injury like a cut) bleeding occurs until a clot forms. Once the site of injury has healed, the blood clot will naturally dissolve. If no blood clot forms it is called a hemorrhage. A hemorrhage is uncontrolled bleeding and can be highly dangerous. Hemophiliacs are people with a blood disorder where there blood does not clot. A small injury can lead to uncontrolled bleeding. In the 1960s, before treatment became available, the life expectancy of someone with hemophilia was just 11 years. Today fortunately, with regular infusions of clotting medications, most can expect to live a relatively normal life expectancy.

How Clots Form

how blood clots form

Stage 1
When the blood vessel wall is broken, thrombocytes (platelets) in the blood (which are easily damaged) disintegrate and release an enzyme called thromboplastin. Thromboplastin then converts a protein in the blood plasma called prothrombin into an active enzyme called thrombin. Calcium is needed for this process to work. (So: thromboplastin + calcium + prothrombin = thrombin). This makes the platelets stickier so they start to bind directly over the site of injury.

Stage 2
Thrombin then changes another plasma protein, fibrinogen into fibrin. Fibrin is insoluble and forms a netlike covering across the damaged vessel. (Thus thrombin + fibrinogen = fibrin).

Stage 3
As blood tries to flow through the net, red and white blood cells and platelets are trapped and form a clot. (Thus fibrin + blood cells = clot).

The following are necessary for a clot to form:

• Prothrombin
• Calcium
• Thromboplastin (produced by damaged platelets)
• Fibrin
• Vitamin K (necessary for formation of prothrombin)

Blood clotting can be affected by:

• A deficiency of platelets as in severe bone marrow diseases.
• Lack of one of the necessary components listed above (caused by diseases such as hemophilia).
• An absence of fibrinogen.
• Lack of Vitamin K which is necessary for the production of prothrombin.
• Lack of calcium.
• An excess of fibrinogen in the blood can cause thrombosis (internal and potentially dangerous blood clots).

When Is A Blood Clot Dangerous?

How an embolism forms
A blood clot forms when red blood cells and fibrin strands clump together. A thrombus is a clot that blocks blood flow. If part of the thrombus breaks away, it is called an embolism.

Sometimes clots form inside vessels where there is no injury and they do not dissolve naturally. Abnormal clots can form in arteries or veins, important vessels that transport blood around the body. Arteries carry oxygenated blood from the heart to the rest of the body and veins carry deoxygenated blood away from the body's organs and back to the heart. An abnormal clot that forms in a vein can restrict blood flow back to the heart, resulting in swelling and pain as blood builds up behind the clot. One type of clot that can form in the leg (or less commonly the arm or pelvis) is called deep vein thrombosis (DVT). If the clot detaches from its point of origin it can travel through the heart to the lungs where it forms a wedge cutting off blood flow. This is a highly dangerous condition called pulmonary embolism. If a clot travels to the head, it can cause a stroke (a brain attack). If it forms or travels to the coronary arteries (the vessels supplying blood to the heart itself), it can cause a heart attack.

Symptoms Of A Dangerous Blood Clot

The symptoms of an abnormal blood clot can vary, according to where it occurs:

Heart: Chest pain that may radiate down the left arm, shortness of breath, sweating. See, signs of a heart attack.
Brain: Slurred speech, problems seeing, weakness and seizures. See, signs of stroke.
Arm or Leg: Sudden pain, swelling and tenderness.
Lung: Severe, sharp chest pain, coughing up blood, rapid pulse, shortness of breath, sweating and fever. See, symptoms of chest pain.
Abdomen: Severe abdominal pain, diarrhea and vomiting.

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