The human lung is supplied by
two arterial systems referred to as pulmonary and bronchial, each
originating from a different side of the heart. Blood from the lungs is drained
by two venous systems, pulmonary and true bronchial. The
pulmonary veins drain oxygenated blood from the regions supplied by the
pulmonary artery and deoxygenated blood from the airways within the lung that
are supplied by the bronchial artery. The true bronchial veins serve only
the perihilar region, supplied mainly by the bronchial artery, and this blood
drains to the azygous system and right atrium.
Arteries
The bronchial arteries arise
from the aorta and supply the capillary plexus of the airway walls from the
hilum to the respiratory bronchiole.
The pulmonary artery
branches run with airways and their accompanying bronchial arteries in a single
connective tissue sheath referred to as the bronchoarterial or bronchovascular
bundle. The pulmonary artery transforms into a capillary bed only when it
reaches the alveoli of the respiratory bronchiole. It supplies all capillaries
in the alveolar walls that constitute the respiratory surface of the lung.
Veins
All intrapulmonary blood
drains to the pulmonary veins. The veins lie at the periphery of any unit acinus,
lobule, or segment. Veins receive tributaries from the alveolar capillary
network, the pleura, and the airways.
Precapillary Anastomosis
Pulmonary and bronchial
arteries, and hence the right and left sides of the heart, communicate through
the capillary bed in the region of the respiratory bronchiole and through the
intrapulmonary venous bed. Pulmonary-to-bronchial artery anastomoses are
present in the walls of the larger airways but normally are closed. They open
if blood flow is interrupted in either system and in certain disease states such
as pulmonary arteriovenous malformation.
