Blood Coagulation

Blood is a very important fluid in the human body that flows under high pressure through our veins and is essential for the proper functioning of the body. The blood is 90 percent water, inorganic salt and protein. Traces of other substances such as organic acids, pigments, enzymes, platelets, WBC, RBC and other enzymes are also present in the blood. Owing to how vital blood is, a significant loss of this fluid may lead to death. To prevent this, our body has an inbuilt blood clotting mechanism. Through this blood clotting process called blood coagulation, the excess loss of blood from our body is prevented. 


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Blood Clotting Mechanism 

The blood coagulation definition states that the blood clotting mechanism is the process through which a thrombus or clot is formed which restricts excess blood from flowing out. This gel-like mass is created from fibrin and platelets. The blood clotting mechanism has various steps that finally result in blood coagulation. Haemostasis (the opposite being haemorrhage) refers to a process which brings about cessation to bleeding and helps the damaged blood vessel to heal with the loss of the blood stopped. The mechanism of blood coagulation is given below:


The First Stage

The mechanism of blood coagulation is known as haemostasis. The first step follows an injury or cut that results in the loss of blood. This initiates the process of vasoconstriction, which causes the walls of the vessels to react immediately and reduce the amount of blood that flows to the infected region. The first stage is essentially healing the wound where the blood starts forming a gel like substance which would prevent further loss of blood from taking place.


The Second Stage

In the second stage of the blood coagulation process the platelets play a significant role in stopping the bleeding in the injured region. This is started by a process called secondary homeostasis that causes a fibrin clot to be formed. The granule contents which are stored include ADP along with thromboxane, which causes the platelets which are within the blood plasma to get activated. However, the platelets by themselves are insufficient in completely securing the injured region and form a blood clot. Here, various other factors come into play that finally activate and assist each other during the clotting cascade. 


The Third Stage

The clotting cascade gives way to the development of fibrinogen, a soluble plasma protein. The fibrin proteins coagulate and form a blood clot. If the protein is composed of only platelets, then it is called white thrombosis, and if the red blood cells are also present, they are termed red thrombosis. This is the final step in the mechanism of blood coagulation.


Deep Vein Thrombosis

The blood clotting process may not always proceed smoothly, as in the case of deep vein thrombosis. Deep Vein Thrombosis or DVT is caused when the blood clot takes place in one or multiple deeply located veins in the body. Generally, after the blood clotting process, these clots dissolve as is natural in the process of blood clotting. However, after dissolving the clots travel through the bloodstream and affect other organs such as the lungs or the chest where they block the flow of bloodstream. The typical symptom of DVT is a pain in the muscles, particularly in the legs along with swelling. Most of the time, the clots occur without any perceptible symptoms. DVT takes place due to medical reasons or the lack of frequency in the body movements. 


Did You Know? 

Various disorders obstruct blood coagulation. One of such disorders is Willebrand disease in which a person is deficient in the VWF protein. When people with the Willebrand disease bleed, they are incapable of forming a platelet plug. Another disorder that affects blood coagulation is haemophilia. In haemophilia, the blood vessels constrict, and the platelets form a plug. One of the essential clotting factor proteins is absent or damaged, and the clot is not made sturdy enough.


Solved Examples

1. What is blood coagulation?

Answer: Blood coagulation or clotting is a process by which the blood transforms from a liquid to a gel-like substance and forms a blood clot. The blood clotting process results in homeostasis and leads to repair of damaged blood vessels after cessation of blood loss. The blood clotting process occurs with the use of platelets and fibrin.

FAQ (Frequently Asked Questions)

1. Describe the Mechanism of Blood Clotting.

Answer: Coagulation is initiated immediately following an injury to a blood vessel which has suffered damage in the endothelium lining. The blood is exposed to the subendothelial space. It gives way to two different processes: the platelets undergo change, and the subendothelial tissue factor is exposed to plasma factor VII, resulting in cross-linked fibrin formation. A plug is formed at the site of injury resulting in primary haemostasis. Secondary haemostasis occurs at the same time. Blood coagulation occurs not only in humans but all other mammals and animals as well. In mammals, the blood clotting mechanism comprises both protein and cellular components.

2. What is Deep Vein Thrombosis?

Answer: Deep vein thrombosis refers to a severe condition that takes place when a blood clot occurs in a deep-seated vein within the body. Blood that has solidified into a lump is called a blood clot. Blood clots form in the deep-seated veins generally in the lower leg or thigh but can also be created in the other parts of the body. The symptoms of the disorder may include swelling in the ankle, leg or foot especially on one side, cramp in the calf, an area of skin feeling comparatively warmer, reddishness or bluishness of the skin in the affected region and severe pain in the foot or ankle region.