Vascular Organization of the Human Placenta

Abstract

THE currently accepted theory of maternal blood flow through the intervillous space of the primate placenta¹ is that maternal blood entering through basally situated spiral arterioles spurts up towards the chorionic plate under the influence of the vis a tergo of the maternal arterial pressure, spreads laterally and falls back to drain through basal venous openings. Short circuiting from artery to adjacent vein is believed to be avoided purely by virtue of the arterial pressure. This theory based on. cineangiographic evidence takes no account of the structure of the foetal portion of the placenta. The latter consists of numerous lobules or cotyledons of which the principal fifty to sixty are arranged in the form of hollow centred bush-like structures as seen in corrosion casts of the foetal vasculature^2,3. Each lobule arises by a main chorionic stem, and is supplied through a major branch of an umbilical artery. Subsequent branches supply an extensive capillary network within the mass of terminal villi which crowd round the central intralobular space. This lobular pattern can be recognized in histological sections in the form of dense masses of villi orientated round cavities⁴. Interlobular and subchorial areas show greater separation between the villi.