Blood Clots (Thrombus, Embolus) – Types, Causes, Symptoms

A blood clot is simply a coagulated mass of blood components that functions as a plug to prevent the loss of blood. The process of clotting or blood coagulation is an efficient life-saving mechanism that is designed to seal any injury to the blood vessel until the wall of the vessel can restore the lining. This process is seen when you develop a scab over a cut or bleeding sore.

Types of Blood Clots

Sometimes a blood clot starts developing inside a blood vessel and this is known as a thrombus. If the the thrombus does not dissolve, it may grow in size until it partially or completely blocks the flow of blood in that vessel (occlusion). Thrombi may develop slowly over time even when there is no visible damage to a blood vessel or no evident site of bleeding. If it breaks off from this site, it can travel through the bloodstream and lodge elsewhere in the body. This freely moving thrombus is called an embolus and can result in a stroke or pulmonary embolism which may be fatal.

Causes of a Thrombus or Embolus

A number of factors may contribute to the development of a thrombus as a result of :

• Damage to the vessel wall. This causes platelets and fibrin to deposit at the damaged site and sometimes trap other blood cells.
• Abnormal flow of blood. A blood vessel is shaped in a manner that allows blood to move freely and rapidly. If there is any deformity, obstruction, slowing or pooling of blood within the blood vessel, the components of the blood may begin to coagulate thereby resulting in a clot.
• Clotting disorders. Certain conditions, including genetic diseases, trauma or drugs, may affect the clotting mechanism thereby causing blood to clot when it should not be doing so.

A clot can develop anywhere in the circulatory system – within both veins and arteries. If it breaks off from the original site where it developed, it becomes an embolus that can lodge elsewhere in the body – usually in small blood vessels through which it cannot fit. A thrombus is the most common cause of an embolus but other substances and particles may also act as an embolus. This includes gases, fat globules, amniotic fluid, tumours and foreign bodies.

Signs and Symptoms of Blood Clots

A thrombus may develop slowly and only partially occlude a blood vessel before the symptoms become evident. An embolus is usually more fast acting and can cause a complete occlusion suddenly.

The symptoms are dependent on the restriction of the blood flow as this impairs oxygen supply to the tissue resulting in ischemia. If the loss of oxygen supply is severe, it can result in an infarct (death of tissue), which is irreversible.

Some of the symptoms that may be seen includes :

• Pain of the affected area.
• Paleness, especially in a limb (arm or leg) that is affected.
• Weak pulse.
• Coldness of the affected area.
• Numbness, tingling or burning sensation.
• Paralysis or muscle weakness.