Pulmonary vascular tree co-develops with airways.
Pulmonary arteries run closely with bronchi.
Zones of lung may develop without normal connections to airways, and are supplied by systemic rather than pulmonary arteries - sequestrations. Normal lung growth requires fetal breathing movements. If fetal lung expansion is restricted, pulmonary hypoplasia results. Infants are born with small lungs and may not survive because of inadequate ventilatory capacity. Pulmonary hypertension is an early and serious complication of LR shunts in which pulmonary arteries are exposed to systemic arterial pressures.