CONCENTRATION OF PLATELET-ACTIVE SUBSTANCES IN ARTERIES
FLOW EFFECTS ON THE CONCENTRATION OF PLATELET - ACTIVE SUBSTANCES in the vicinity of mural micro-thrombi.
Platelet thrombi growth: At surface of artificial organs, sites of intravasc.
injury, positions of atherosclerotic lesions.
- Platelets adhere to the wall and form a mural aggregate (convection
and reaction of platelets with the wall).
- In the vicinity of the aggregate a region of high conc. of thrombotic
subst. is generated, platelets flowing in this region become activated by
the liberated subst., and interact with the already adherent platelets
forming the thrombus.
Local level of the conc. of the thombotic subst. depends on the rate of
generation and on the convective and diffusive transport.
Thrombogenetic substances: Prothrombin, Thrombin, AT III, Thromboxane A2, ADP
REACTION-EMISSION-TRANSPORT MODEL - Thrombin:
Prothrombin: Diffusive and convective transport in blood
- PROTHROMBIN (A) ® THROMBIN (B)
Th. is being produced at the thrombus surface from Proth. at a rapid rate
Thrombin: Diffusive and convective transport in blood
- THROMBIN (B) + ANTITHROMBIN III (C) ® INACTIVE COMPLEX (D)
Th. formed is inhibited by Antith.III in the bulk to form an inactive
complex; fluid phase reaction 2nd order.
(Rate of reaction is a strong function of Heparin concentration, an
antithrombotic substance), Antithrombin III: Diffusive and convective transport in blood
(Reaction-emission-transport model: L.V. McIntire, Duke Univ.)
THROMBUS GROWTH
THROMBIN CONCENTRATION in the vicinity of a microthrombus, Influence of shear rate
Model: Microthrombus as semi-sphere attached to a plane surface
Emitted molecules bit a traveling platelet (which is passing in the vicinity
the thrombus): Activation, adhesion ® thrombus growth.
WSS CONTOURS
Thrombus: d = 10 mm
Shear field: g = 100 s-1
- Separation zones: Low convection ® local concentration max.
- Flow disturbances are responsible for local conc. changes near the growing thrombus.
ÞThe resulting thrombin conc. exceeds the required level for platelet activation.
THROMBIN CONCENTRATION
at radial distances 0,1,3 mm at symm.plane
THROMBIN CONCENTRATION contours under presence of HEPARIN in blood
The inactivation of Thrombin: Reaction with the protein AT III can be increased
with additional HEPARIN (antithrombotic substance; reaction coefficient k)
 |  |
| at the symm. plane | at a distance of 1mm from the wall |
Inactivation of thrombin by antithrombin is much stronger if Heparin is present.
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