Estimation of clotting time
Clotting time of the blood is the time required for the blood to clot after it has come out of the vessel.
Glass slide, stop watch, pin/needle, lancet, alcohol, cotton.
Wipe the ball of your finger with cotton dipped in alcohol. Allow to dry.
Prick your finger with the lancet.
Start the stop watch as soon as the flow of the blood starts.
Place 2-3 drops of blood on the slide.
At every 15 seconds, draw a pin / needle through the drop of blood until it picks up a fibrin thread.
Stop the watch & note the time.
The moment at which fibrin threads appear is the end point.
The time interval from the start of the blood flow to the appearance of fibrin threads denotes the clotting time.
Result: The clotting time was determined as ---
Blood maintains its liquid state as long as it remains in the blood vessel. If it is drawn from the body, it thickens and forms a jelly. This jelly or clot contracts or shrinks and a straw-coloured fluid called serum is squeezed out from it. If shed blood is microscopically examined, very fine threads will be seen. These threads entangle the blood cells and together with them form the clot.
The process of clotting is called blood coagulation or haemostasis. Its purpose is to prevent blood loss when a blood vessel is ruptured. The normal coagulation time varies from 3 to 8 minutes.
Four substances are necessary for the coagulation of blood: prothrombin, thromboplastin, calcium and fibrinogen. Fibrinogen, prothrombin and calcium are present in the circulating blood.
Thromboplastin is present in the tissues. When the blood is shed thromboplastin is liberated from the injured tissue. The thromboplastin acting upon the prothrombin in the presence of calcium converts into active thrombin.
Thrombin acts in turn upon the soluble protein fibrinogen converting it to insoluble fibrin which is deposited as fine threads to form the framework of the clot.
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