KEY POINTS

Pulmonary Circulation

1. The structure of the small pulmonary arteries varies among species.

2. Functionally, pulmonary blood vessels can be classified as alveolar and extra-alveolar vessels.

3. The pulmonary blood vessels offer a low resistance to flow.

4. The distribution of pulmonary blood flow within the lung is influenced by several factors.

5. Passive changes in vascular resistance result from changes in vascular transmural pressure.

6. Neural and humoral factors cause contraction of the muscular pulmonary arteries.

7. Alveolar hypoxia is a potent constrictor of small pulmonary arteries.

8. During exercise the pulmonary circulation must accommodate a large increase in blood flow.