Blood clots

Blood normally flows smoothly inside blood vessels – the arteries and veins. The wall of these vessels has outer and middle layers made of muscle and connective tissue, and a delicate inner lining called endothelium made of a single layer of cells that allow smooth, uninterrupted blood flow.
When a blood vessel is cut or ruptured in an injury, hemostasis or prevention of blood loss occurs. This comes about through blood vessel wall contraction, adhesion, and aggregation of platelets from the blood leading to the formation of a platelet plug, and blood coagulation. A blood clot is then formed as part of hemostasis a protective mechanism of the body to prevent blood loss when an injury occurs.
In normal conditions, clot formation is a protective mechanism. It is a first line of defense of the body to stop bleeding because it acts as a plug that helps prevent blood loss when there is an injury. The blood clot is then normally broken down by the body as healing occurs.
Thrombosis is the medical term for the formation of a blood clot (called thrombus) inside a blood vessel. It occurs either inside veins or inside arteries. Veins are the blood vessels that carry blood from different parts of the body to the heart and to the lungs for oxygenation while arteries are the vessels that carry oxygenated blood from the heart to the different body parts.
A blood clot in a vein can be dislodged and can travel to other parts of the body in a process called embolism. In deep vein thrombosis, blood clot forms in a deep vein usually in the lower leg, thigh, or pelvis. If part of the blood clot breaks and the fragment goes to the lungs it is called pulmonary embolism, a serious medical condition that can be fatal if the fragment is big.
If the blood clot occurs inside an artery, blood flow and oxygenation of an organ is impaired.
If the clot blocks blood flow to the brain, this would cause stroke. If the blood flow to the heart is blocked, heart attack can occur.
Any person can develop thrombosis, but risk factors increase the chance of having a blood clot inside a vein or artery. Risk factors for arterial thrombosis include smoking, diabetes mellitus, high blood pressure, older age, elevated cholesterol, lack of exercise, obesity, immobility such as after surgery, lack of activity such as on a long trip, and family history of arterial thrombosis.
Also, autoimmune disorders that make blood more likely to clot such as in systemic lupus erythematosus.
Arterial thrombosis may occur due to arteriosclerosis or hardening of arteries. Fatty or calcium deposits that accumulate through the years cause arterial walls to thicken. This can lead to a buildup of a plaque or fatty material in the arterial walls. The plaque can eventually rupture and injure the vessel wall, leading to blood clot.
The risk factors for venous thrombosis include immobility such as after surgery, inherited blood clotting disorders, presence of central venous catheter, smoking, older age, pregnancy, obesity, family history of deep vein thrombosis (DVT), previous history of DVT, use of hormone therapy or birth control pills, surgery, fracture, trauma, lack of activity during long trips and some ailments like cancer, heart, lupus, and lung disease.
Symptoms of thrombosis may be nonspecific and can be like symptoms of other illnesses. These include pain in one leg, chest pain, swelling in the leg or arm, change in mental status like confusion or drowsiness and weakness or numbness on one side of the body if blood flow to the brain is blocked.
The European Medicines Agency’s safety committee, the Pharmacovigilance Risk Assessment Committee has confirmed on March 18, that the AstraZeneca vaccine is not associated with an increase in the overall risk of blood clots in those who receive it.
It confirmed the benefits of the vaccine in combating the still widespread threat of Covid-19 (which itself results in clotting problems and may be fatal) continue to outweigh the risk of side effects.