Microvasculature of the rat lung as revealed by scanning electron microscopy of corrosion casts.

The pulmonary microvasculature of rats was studied by injection replicas prepared from Mercox. This medium enabled us to easily obtain consistant, stable and complete injected replicas of the pulmonary vasculature. The pulmonary arteries repeated branching as far as the pulmonary arterioles, and then formed rich, basket-like anastomosing capillary networks in the alveolar walls. These capillary networks were collected into the tributaries of the pulmonary veins. The walls of the pulmonary veins, down to small branches of approximately 100 micrometers in diameter, were surrounded by one to three layers of circular or obliquely oriented capillaries with longitudinal connections. The pulmonary artery had only a single layer of capillary network in the adventitia. The vasa vasorum of the pulmonary vessels were collected into venules. They were confluent to the bronchial veins outside the lung and into the tributaries of the pulmonary veins within the lung. The bronchial tree was supplied by the bronchial arteries which form the coarse capillary plexus extending as far as the terminal bronchioles. The trachea and the proximal parts of the bronchi drained into the bronchial veins connected with the superior vena cava. The distal parts of the bronchial tree drained into the tributaries of the pulmonary veins, or adjacent capillary networks in and around the alveolar walls.