Pulmonary Veins (Formation of the Left Atrium)

Figure 1

Development of the left atrium occurs concurrently with that of the right atrium. During the early part of the fourth week an outgrowth of the pulmonary veins appear from the left atrium. This "sprout" will bifurcate until there are four veins. These vessels will then grow towards the lung buds.

• LA = Left atrium
• OPV = oriface of pulmonary vein
• PV = pulmonary vein

Figure 2

The left atrium begins to expand gradually intussuscepting the four branches. As the atrial wall expands, the smooth tissue of the pulmonary veins is incorperated into the wall of the atrium and displaces the trabeculated tissue anteriorly and laterally which will then form the adult auricles. Compare this process to the formation of the adult right auricle.

• LAu = Left auricle
• OPV = Oriface of the four pulmonary veins
• PV = four pulmonary veins