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. 1. The bronchial circulation provides a blood supply to airways, large vessels, and, in some species, the visceral pleura. Alveolar vessels are the thin-walled capillaries that perfuse the alveolar septum (Figure 46-1). They are exposed almost directly to the pressure changes that occur in the alveoli during breathing. Extra-alveolar vessels include the pulmonary arteries, and veins, which occur together with bronchi in a loose connective tissue sheath called the bronchovascular bundle. This bundle is bounded by a limiting membrane to which alveolar septa are attached (Figure 46-2). The behavior of extra-alveolar vessels is determined by pressure changes within the connective tissue space of the bronchovascular bundle, which approximate pleural pressure, rather than by changes in alveolar pressure. The bronchovascular bundle is also the initial site of accumulation of edema fluid when animals develop pulmonary edema.
Pulmonary Blood Flow
Pulmonary Circulation
Functionally, Pulmonary Blood Vessels Can Be Classified as Alveolar and Extra-Alveolar Vessels
Passive Changes in Vascular Resistance Result from Changes in Vascular Transmural Pressure
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Pulmonary Blood Flow
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