Vascular Endothelium - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 594

leukocyte

flow

platelet

coagulation factors
fibrinolysis

adhesion

aggregation

stress

glycocalyx +

− +

− −

endothelium

adhesion
molecules

cytoskeleton

GFR

basement membrane

+ −

extracellular matrix
(proteoglycans, collagen, elastin, ...)

(growth factor store)

growth
vasomotor tone

smooth muscle cell GFR

macrophage

fibroblast

Fig. 9.11 Vascular cells are responsible for local regulations: (1) adaptive responses to hemody-
namic stresses that direct the vessel caliber; (2) control of proliferation of vascular endothelial
and smooth muscle cells; (3) prevention of blood coagulation and platelet aggregation in normal
conditions; (4) prevention of leukocyte diapedesis in the abscence of inflammatory response.
Vascular cells bear time-dependent 3D shearing and stretching from flowing blood. Both stress
types vary strongly in magnitude during the cardiac cycle. Whereas stretching results from high-
amplitude pressure applied perpendicularly to the wall, the wall shear stress exerted tangentially on
the wall-blood interface has a low magnitude and its direction, besides its amplitude, can change
during the cardiac cycle, in the case of flow reversal during diastole. Even in static conditions, the
extracellular matrix influences cell adhesion and spreading, as well as differentiation, migration,
and apoptosis.

( q ) remains constant owing to adaptive response of the local artery bore, hence local
resistance ( = cst. Therefore, when the blood pressure rises, the resulting

vasoconstriction to maintain the flow rate further elevates blood pressure, hence the
cardiac load.
On the other hand, large arteries can be supposed to modulate this reflex vaso-
constriction in resistive arteries, as they can reset stress and strain field experienced
in their walls, thereby reducing the cardiac postload. This additional mechanotrans-
duction effect aims at maintaining the cardiac postload in the physiological range.
In other words, when the blood pressure ( p

): q = p / R

R

) soars, large arteries will dilate
to lower local resistance. Vascular smooth myocytes that sense pressure-induced
intramural stretch immediately react by fluidizing their stress fibers and relaxing.

= q

R