Adaptability of endothelial orientation to blood flow dynamics--a morphologic analysis.

Vascular endothelium has a certain specificity in its anatomical orientation. The long axis of the endothelial cell and the shingle effect of cell process overlapping is always oriented parallel to the direction of blood flow. To determine whether this specific anatomical orientation would be maintained when the direction of blood flow was altered, twenty ilio-femoral vein segments and twenty vascular patches of carotid artery and jugular vein were studied. Valvulotomised ilio-femoral vein segments (n = 20) were interposed into adjacent arteries in a non-reversed fashion (the direction blood flow is reversed to the cell process overlapping). One centimeter-square carotid artery and jugular vein patches (n = 20) were rotated 90 degrees (endothelial cell orientation is perpendicular to the direction of blood flow). Reversal of endothelial cell overlapping to complement the complete reversal of the direction of blood flow exists in the vein graft through re-endothelialisation and endothelial reorientation. The process of endothelial reversal occurred in stages (endothelial cell process retraction, interdigitation, complete reversal) and was completed within 8-16 days. In the vascular patch, endothelial re-orientation occurred in 8 days through cell re-orientation and replacement. Mitosis was not encountered in either study. This report highlights certain functions and the adaptive capability of endothelial cells to complement the direction of blood flow.