Three cell types comprise the vessel wall: endothelial cell the intima, smooth muscle cell or its precursors the media, and fibroblast the adventitia. In health or disease anatomic level determines response to injury or to physiological stimulus - arteries, veins, capillaries and pre and post capillary segments, including non and partially muscular vessels each show characteristic behaviour. In hypertension, hypertrophy and hyperplasia differentially affect each cell type, and, in microvessels change in phenotype also - precursor muscle and fibroblast develop contractile features. In established pulmonary hypertension of whatever cause, structural or full changes reduce vascular volume, so patent vessels are susceptible to high flow injury. Pulmonary hypertension a black box, reflects structure and function. Each cause of hypertension leaves its imprint on structure and reactivity. The features peculiar to each of three types are considered - persistent pulmonary hypertension of the newborn focuses on vascular growth and maturation, primary pulmonary artery hypertension on an intrinsic microvascular lesion and high flow on injury. Angiogenesis includes sprouting of vessels as well as structural remodelling. The latter occurs in pulmonary hypertension, but angiogenesis is not typically a causative factor although it may occur in advanced injury.