Intussusceptive microvascular growth, a new mechanism of capillary network formation.

Growth by intussusception is defined as growth by deposition of new particles or pieces of formative material among those already embodied in a tissue or structure. In the context of capillary growth the term stands for the extension of the capillary system by the insertion of new capillary meshes within the existing network. New meshes arise as slender transcapillary tissue pillars. These are formed initially by a circumscribed fusion of opposite endothelial leaflets. Following reorganization of the junctional complexes, the pillar is invaded by interstitial tissue. This means that for the formation of new capillaries no sprouting of endothelial cords or tubules is required. The mechanism is described in the growing lung, but may occur in other tissues too. There may be a chance for in vivo observation of the process in the capillaries of the chorio-allantoic membrane of the chicken.