Angiogenesis

Abstract

The starting point in the regeneration of vascularization by angiogenesis is pre-existent intact capillaries around damaged tissue. The sequence of reaction is:

• Engorgement, increase in permeability of vessels; loosening of cell junctions; disruption of basal membrane of intact capillaries.

• Movement of endothelial cells through their own basal membrane towards source of angiogenic stimulus and via secretion of degradative proteinases.

• Formation of cords of endothelial cells and sprouts.

• Proliferation of endothelial cells within the sprout but not usually in its tip.

• Simultaneous proliferation of pericytes and fibroblasts of perivascular tissue.

• Average capillary growth rates between 1,2 and 3 mm/day.

• Growth of capillary sprouts appear to follow the path of least resistance.

• The tip of one sprout joins with another to form a capillary loop.

• The lumen of new vessels develops between overlapping cells within the sprouts by the accumulation of blood and tissue secretions in the intercellular space.

• New basal membrane is laid down around the new vessels with the participation of pericytes.

• Fibroblasts migrate towards the new vessel, surround it and subsequently develop into the cellular and adventitial layer.

• Reticular and collagen fibrils are first seen four to 7 days after the initiation of fibroblast migration.