Principle: Bleeding time is the time taken between the appearance of blood to the cessation of blood.
Apparatus: Needle, blotting paper, stop watch.
Principle:
Bleeding time is the time from the onset of bleeding till the stoppage of bleeding from the injured surface. Bleeding time depends on the effectiveness of vasoconstriction and platelet plug formation of haemostasis process.
During an injury the vascular response is the immediate response. The contraction of smooth muscles of the blood vessels is potentiated by the release of chemicals like serotonin ( 5-HT ) from the aggregated platelets at the site of injury. Hence this process is a fast process and this method determines the function of plateletsand integrity of the capillaries.
Procedure:
Clean the fingertip with spirit and allow it to dry. Make a deep prick. Blood will start flowing. Note the time. With the blotting paper touch the blood coming after each 1/2 minutes. A fresh part of blotting paper should be used each time. Note that the blood spot on the filter paper gets thinner, till it disappears and the bleeding stop. Note the time. The time, in interval gives the bleeding time.
Discussion:
The time elapsed between the moment blood escapes from vessels and the cessation of its flow is defined as the "bleeding time". The usual bleeding time is 1-3 minutes. The bleeding time is affected by various factors such as the size and shape of injury, endothelial smoothness, the muscularity and elasticity of blood vessels, sealing of dents by platelets, pressure difference between inside and outside of blood vessel. Bleeding time is prolonged during thrombocytopenia, (decrease in platelet count) and scurvy ( Vit - C deficiency). The capillary contractility and platelets play an important role in cessation of bleeding . These are relatively simpler mechanism than the mechanism of clotting. Hence bleeding time is shorter than clotting time. Purpuria is the condition associated with platelet deficiency and characterized by the appearance of spots on skin and prolonged bleeding time.
Result: Bleeding time of the given sample of blood is 1 min. 30 sec. .
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