Experiment 6
Suaad Mohammad (M.Sc.)
The term hemostasis means prevention of blood loss. Whenever a vessel is severed
or ruptured. Hemostasis is achieved by several mechanisms:
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Vascular constriction (Vascular spasm).
Formation of platelet plug.
Formation of a blood clot as a result of blood coagulation.
Eventual growth of fibrous tissue in to the blood clot to close the hole in the
vessel.
A- Bleeding Time:
Bleeding time is defined as the time taken for a standard skin wound to
stop bleeding. Upon vessel injury, platelets adhere and form a hemostatic
platelet plug. Bleeding time measure the ability of these platelets to arrest
bleeding.
Bleeding time is performed as a screening procedure used to detect
both congenital and acquired disorders platelet function. So the duration of
bleeding from standard puncture wound of the skin is a measure of the
function of platelets as well as the integrity of the vessel wall.
Procedure
1- Clean the tip of a finger (or the lobe of the ear) with alcohol and let
dry.
2- Pierce the tipoff a finger with the lancet, making the incision 3 mm
deep. Start the stopwatch.
3- Blot the blood with the filter paper at regular 30 second intervals.
Move the filter paper so that each drop of blood touches a clean
area. Do not touch the incision with the filter paper.
4- When the filter paper no longer shows signs of blood, stop the
stopwatch and record the time.
Normal Values : 1 to 5 minutes.
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B- Coagulation time (Capillary tube method)
In order for blood to clot, the enzyme thrombin must be generated from
the plasma precursor prothrombin. Thrombin then converts soluble
fibrinogen into insoluble fibrin. Generation of thrombin involves the
sequential activation of a number of other plasma clotting factor, this
process is also being assisted by Ca++ and by factors released by platelets
and damaged tissues . The time taken for blood to clot mainly reflects the
time required for the generation of thrombin in this manner. If the plasma
concentration of prothrombin or of some of the other factors is low (or if
the factor is absent, or functionally inactive), clotting time will be
prolonged. The expected range for clotting time is 4-10 mins.
Procedure
1- Clean your finger with alcohol and let dry.
2- Pricked the finger by lancet, remove the first drop of blood.
3- Squeeze the finger to obtain a large drop of blood, and fill the
capillary tube with blood.
4- After one minute start breaking small pieces of the capillary tube
every 30 second until a fibrin thread is seen between the two broken
ends.
5- By these methods the normal clotting time is 5 to 10 minutes at 37
C°.
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