![]() ![]() As a result, the deep bronchial system effectively functions as an arteriovenous shunt. However, the deep circulation drains into the pulmonary vein and thus left ventricle. The superficial system drains into the hemiazygos and azygos veins, which ultimately drain into the right heart with the systemic venous return. The bronchial circulation has superifical and deep systems. In addition to the pulmonary circulation, the lung parenchyma receives oxygenated blood via the bronchial circulation (accounting for about ~1% of the cardiac output) which arises from the aorta, and thus left ventricle. The large negative pleural pressure (approximately -4 to -7 mmHg) exists because of an efficient efferent venous and lymphatic system that keeps the alveoli closely tethered to the visceral pleura and prevents them from collapsing inwards. It is appropriate to mention that a similar system of lymphatics and vessels exists between the parietal and visceral pleurae, draining the pleural fluid which plays an important role in providing a viscous medium for expansion of lungs during their respiratory excursion. They can be found close to the terminal bronchioles and drain the mediastinal lymphatics before emptying into the right lymphatic duct. Lymphatics play a crucial role in maintaining a dry alveolar membrane and preventing accumulation of tissue fluid around the pulmonary circulation. ![]()
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