Mathematical Models for Blood Coagulation - Fluid-Structure Interaction and Biomedical Applications - page 484

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Fig. 7.2 Schematic representation of main platelets receptors

described in the sequel. Drugs neutralizing some of the receptors are administered
to prevent blood clotting, particularly after heart surgery. The most known among
a long list are Plavix (Clopidogrel), acting on the ADP and other receptors, and
Aspirin , inhibiting the Thromboxane A2 production. A natural platelet inhibitor,
synthesized in the endothelium, is NO ( nitric oxide ). Platelets exhibit also an intense
internal activity, since they possess corpuscles, called Ǜ- granules and dense (or
ı) granules .TheǛ- granules secrete, under activation, the binding factors vWF
and Fibrinogen (see Coagulation Factors) in addition to Platelet Factor 4 (another
platelet activator) and other proteins having different functions. For instance,
Thrombospondin 1 , a multifunctional protein (e.g., antiangiogenic), and Nexin II ,
whose role will be discussed later. Platelets also release Growth Factors which help
repairing the damaged tissue. The ı- granules produce platelet activators like the
already mentioned Thromboxane A2 and ADP, thus triggering positive feedback,
but also Serotonin (5-hydroxytryptamine), a vasoconstrictor. Activated platelets are
also able to synthesize some of the coagulation factors.
An important role in platelets (and other cells activity) is played by the
membrane . Not only through the receptors, but also by exposing negative charges to
the exterior, which become sites of attraction of active coagulation factors.
Finally, we recall that in most cases the presence of the ion Ca++ is necessary
for receptors to perform their action. Such an ion is also contained in the ı-granules.
Drugs containing citrates have the effects of lowering Calcium concentration,
inducing some anticoagulant effect. Therefore their use must be avoided while
assuming potent anticoagulants.
Literature on platelets is extremely large and includes several topics (e.g., [ 171 ],
whose foreword [ 50 ] contains a huge bibliography). An accurate review paper on
platelets receptors is [ 207 ], also with numerous references.

2. White Blood Cells (WBC)

Also called Leukocytes , they are distinguished in various classes ( Granulocytes :
neutrophils, eosinophils, basophils; Lymphocytes , including T-cells; Monocytes ,
further differentiated in Macrophages ) possessing nuclei with different shapes.