Rush Center for Congenital
and Structural Heart Disease




Pulmonary circulation


Airways, lung parenchyma and distal pulmonary arteries

On the 21st day of development a groove forms in the floor of the fore gut, just ventral to heart.  This is termed the pharyngeal groove; it develops to form the pharynx.  On day 23, the laryngotrachial groove, a median structure in the pharyngeal region is noted.  The edges of the laryngo-tracheal tube fuse to form the larynx and trachea cranially, and the right and left main bronchi and right and left lung buds distally.  The growth and branching of the lung buds, together with the surrounding mesoderm form the distal airways, lung parenchyma and pulmonary blood vessels.  By the 16th week of gestation, a full complement of preacinar airways and blood vessels will have formed; thereafter it is a matter of growth of these structures.  The pulmonary arteries in-utero are muscular, similar to that of the aorta, these thick walls extend much further into distal pulmonary arteries than what is seen in adults.  The thinning of distal pulmonary arteries occurs post-natally as the pulmonary vascular resistance drops after the onset of breathing and improved oxygenation [376].  

Proximal pulmonary arteries

The proximal main pulmonary artery develops from the truncus arteriosus, while the distal main pulmonary artery and the proximal right and left pulmonary artery develop from the ventral 6th aortic arch arteries.  The distal right and left pulmonary arteries form from the post branchial arteries which develop from the lung buds and surrounding mesoderm.  The ductus arteriosus develop from the distal left 6th aortic arch.

Pulmonary venous system

A primitive vein sprouts out of the left atrium, which bifurcates twice to give four pulmonary veins which grow towards the developing lungs.  The lung buds develop from the foregut.  A plexus of veins is formed in the mesoderm enveloping the bronchial buds; these veins will meet with the developing pulmonary veins out of the left atrium to establish a connection at the fifth week of development.  As the left atrium develops it progressively incorporates the common pulmonary vein into the left atrial wall until all four pulmonary veins enter the posterior wall of the left atrium separately.  The incorporated pulmonary veins form the smooth posterior wall of the left atrium, while the trabeculated portion of the left atrium becomes more ventral in location [362, 364].