What Causes a Blood Clot?

Blood clots normally form to stop bleeding by sealing small cuts or breaks in the walls of blood vessels. Anytime you have a cut or a bruise, the blood will clot to stop the bleeding. This occurs in a four-step process of hemostasis (stopping blood flow):

Step 1: Back pressure by surrounding tissue and constriction of blood vessels (vasoconstriction) attempts to close the damaged area to minimize blood loss. In this stage, the nervous system induces cells to release chemical substances that cause vasoconstriction (serotonin, thromboxane A2, epinephrine, fibrinopeptide B).

Step 2: Platelets (thrombocytes), which are irregularly-shaped cell fragments, are activated to form a temporary plug. The platelets adhere to injury sites mainly due to a substance called Von Willebrand factor.

Step 3: An enzyme called thrombin converts the substance fibrinogen to fibrin, which acts as a type of mesh, binding platelets together and enabling a more stable blood clot. There are many pathways involved in this complex process.

Step 4: Blood clots are broken down by a process called fibrinolysis. The blood clot is broken apart when an enzyme called plasmin cuts the mesh of fibrin. The platelets are then removed by other enzymes or through the kidneys and the liver.

The normal formation of blood clots is called coagulation. In normal clotting, platelets plug tears in the blood vessel and are reinforced by clotting factors, including fibrin. Other cells, such as red and white blood cells, may be caught in the ‘web’ of fibrin, further reinforcing the clot.

Abnormal or excessive blood clotting is caused when the process of clotting occurs dysfunctionally. This can be due to diseases and conditions, medicines, genetic mutations, dehydration, smoking, and more.

When abnormal blood clotting occurs, it is referred to as hypercoagulation or thrombophilia. Thrombophilia can lead to blood clots inside of blood vessels (thrombosis), which can lead to obstruction of blood vessels. Also, these blood clots can break free of the blood vessel wall, resulting in an embolus, which can then move through the blood stream and lead to obstruction in any region of the body, including the heart and the brain.

There are numerous conditions that can lead to abnormal blood clotting. These include:

• Antiphospholipid Antibody Syndrome (APS)
• Bone Marrow Disorders
• Thrombotic Thrombocytopenic Purpura
• Disseminated Intravascular Coagulation
• Problems with Blood Clot Breakdown
• Atrial fibrillation
• Atherosclerosis
• Diabetes
• Vasculitis
• Heart failure
• Metabolic syndromes
• Genetic mutations
• And more

There are also many situations that can make blood clots more likely to form. These include:

• Increased homocysteine levels
• Smoking
• During or after pregnancy
• HIV and HIV treatments
• Medications including birth control pills and estrogen hormones
• Long-term bed rest
• Sedentary lifestyle
• Crossing your legs for long periods when sitting
• Sitting for long periods of time
• Long-term use of intravenous catheters
• Organ or device transplants

For normal blood clotting to occur, all of the organs and systems of the body must be properly integrated, which occurs mainly through the nervous system and intercellular communication. When the nervous system is unable to properly communicate with organs, tissues, glands, cells, and other brain regions, any number of symptoms can develop, including abnormal blood clotting.

The biggest risks involved with abnormal or excessive blood clotting are limited or blocked blood flow. Blood clots can travel through arteries and veins and end up anywhere in the body, limiting or blocking blood flow to or from that region. For example:

• If the region is the heart, it can lead to angina or heart attack.
• If the region is the brain, it can lead to stroke.
• If the region is the lungs, it can lead to pulmonary embolism.
• If the region is the legs, it can cause deep vein thrombosis.
• If the region is the kidneys, it can cause renal vein thrombosis.
• If the region is the intestines, it can cause mesenteric ischemia or mesenteric venous thrombosis.
• And so on.

Limited or blocked blood flow of an artery can cause decreased oxygenation (hypoxia or ischemia) or no oxygenation (anoxia), which can lead to death of tissues in the region affected. Limited or blocked blood flow through veins can cause fluid buildup and swelling (edema).

What’s important to understand here is that blood clots can lead to serious problems throughout the body. We also must remember that all of the functions of the body are interconnected, so if you have damage in one region, it can ultimately lead to damage in another region or regions. A good example of this is stroke, which can cause motor dysfunction or paralysis, cognitive problems, organ dysfunction, and even death.

For more information on blood clotting, read my article on vascular conditions, or my article on strokes.

Resources

1. American Heart Association. Understanding Your Risk for Excessive Blood Clotting. Accessed November 18, 2014. Available at: http://www.heart.org/HEARTORG/Conditions/More/Understand-Your-Risk-for-Excessive-Blood-Clotting_UCM_448771_Article.jsp
   
2. National Institutes of Health (NIH) Medline Plus. Blood Clots. Accessed November 18, 2014. Available at: http://www.nlm.nih.gov/medlineplus/ency/article/001124.htm
   
3. National Institutes of Health (NIH) Medline Plus. Pulmonary Embolus. Accessed November 18, 2014. Available at: http://www.nlm.nih.gov/medlineplus/ency/article/000132.htm
   
4. National Institutes of Health (NIH) National Heart, Lung, and Blood Institute. What Causes Excessive Blood Clotting? Accessed November 18, 2014. Available at: http://www.nhlbi.nih.gov/health/health-topics/topics/ebc/causes.html
   
5. Rhoades RA, Bell DR. (2013) Medical Physiology: Principles for Clinical Medicine (4th Edition) Wolters Kluwer. Lippincott Williams & Wilkins.
6. Schafer AI. Thrombotic disorders: hypercoagulable states. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 179.