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Microcirculation Factor: White Blood Cells
White blood cells (leukocytes) may also dramatically affect the resistance to flow. As blood exits the capillaries, there is a phase separation of white blood cells (WBCs) and red blood cells (RBCs).
As RBCs exit the capillaries, they push the WBCs toward the wall and enable then to roll along the endothelium. Specific adhesion molecules on the surface of the endothelium and WBCs enhance their adhesiveness and enable them to roll along the wall for considerable distances.
During inflammation, the adhesiveness of the venule wall increases and WBC rolling is increased leading to their subsequent firm adhesion. Shown above is the rapid increase in WBC rolling and adhesion in response to the peptide fMLP that mimics inflammatory products released within the tissue.