QUESTIONS & ANSWERS: GLOSSARY

IIb/IIIa antagonism platelets (thrombocytes)

Platelets are cells in the blood which initiate thrombosis within arteries.

These cells are activated in the presence of an arterial narrowing and then release serotonin, a chemical which activates more platelets leading to a growing platelet-rich thrombus.

Additional chemical pathways within the platelets are carried by thromboxane (antagonised by aspirin), and adenosine diphosphate (ADP, antagonised by clopidogrel).

The final event in the initiation of thrombosis by platelets is their binding, via the IIb/IIIa platelet receptor, to fibrinogen. Blockade of this final event, using antibody or antagonist, leads to bleeding. There is less bleeding if the thromboxane or ADP pathways are blocked, and least of all when the serotonin receptor "5HT2 receptor" is blocked.

Platelets are also activated by adrenaline and noradrenaline.

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