FUNCTIONS OF PLATELETS AND ORAL ANTICOAGULANTS

 

. FUNCTIONS OF PLATELETS

Platelets/Thrombocytes are biconvex discs produced by bone marrow

Size: 2 to 4μ

Normal count: 1.5 to 4 lakhs/cumm of blood

Granules of platelets: α granules and dense granules

                      α granules : consists of factor V, Fibrinogen, Von williebrand Factor, Platelet

                                            factor IV, PGDF

                      Dense granules: Consists of ADP, Calcium, serotonin

Functions of Platelets

1.       Primary hemostasis – Arrest of bleeding by temporary platelet plug formation is referred as primary hemostasis.

Injury to wall of blood vessel

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Exposure of collagen

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Platelet adherence to damaged vessel wall

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Release of ADP and Thromboxane A₂

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Activation of more platelets

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Aggregation and adherence of platelets (enhanced by platelet activation factor produced by platelets and macrophages)

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Temporary platelet plug

 

1.       Secondary Hemostasis: Arrest of bleeding by the definite clot formation is called secondary hemostasis

Platelet phospholipids and platelet activation factor III are the factors which are involved in clotting.

2.       Clot retraction: Contraction of contractile proteins (actin, myosin and thrombosthenin) present in the platelets play an important role in clot retraction

3.       Repair of capillary endothelium: Platelets adhere to the von – willebrand factor in the wall of damaged blood vessels and release platelet derived growth factor (PDGF). This factor plays an role in the repair of endothelium

4.       Vasoconstriction: Platelets release serotonin which is a vasoconstrictor.

5.       Defense /Phagocytosis: Platelets are helpful in phagocytosis of carbon particles, viruses and immune complexes

Oral Anticoagulants

Refers to anticoagulants which are used as drugs. These substances are given through mouth to prevent clotting.

The substances which are used as oral anticoagulants - coumarin derivatives (Dicoumarol and warfarin)

Dicoumarol

-          It is a synthetic product

-          It resembles vitamin K in structure

Mechanism of action

-          Vitamin K is required for synthesis of clotting factors II, VII, IX, X protein C and Protein S

-          By competitive inhibition with Vitamin K, dicoumarol inhibits the synthesis of the above factors from liver

Other Vitamin K antagonists

            Warfarin, Phenindione, Nicoumalone

Therapeutic use:

Patient with hypercoagulability (increased tendency of blood to clot) are given these oral anticoagulants for preventing the formation of thrombus

Oral anticoagulants are not effective invitro as they are vitamin K competitive inhibitor and can act only inside the body