Figure 13.7 • Intrapulmonary Blood Circulation – The pulmonary circulation is a low–pressure, low–resistance circulation. Blood from the right ventricle and pulmonary artery is distributed to the pulmonary capillaries, where gas exchange takes place. The interface between the alveolar lumen and pulmonary capillary blood consists of a single layer of alveolar epithelium, basement membrane, and the one–cell–layer–thick capillary endothelium. Capillaries cover alveoli in this manner, providing for efficient gas exchange.