The main role of the pulmonary vascular tree is in respiration: the uptake of oxygen and the elimination of carbon dioxide. At the alveolar level, blood vessels are lined only by endothelial cells that come in close proximity with epithelial cells, on the luminal side of the airways. The endothelial cells lining the vessels are in contact with each other, making the vascular wall a tight barrier. Any breach in the endothelial cells barrier results in leakage of fluid from the lumen of the vessels into the interstitial tissue and/or alveolar lumen, severely impairing gas exchange. Disruption of the vascular barrier is a prominent feature of acute lung injury syndrome and results in pulmonary edema formation and subsequent respiratory dysfunction or failure. The endothelial barrier integrity is the result of a balance between the tethering and contractile forces acting on endothelial cells, which are critically dependent upon cytoskeletal components, including the actin-based microfilaments, intermediate filaments, and microtubules .
Endothelial cell activation by inflammatory stimuli is often accompanied by enhanced cellular contraction and formation of intercellular gaps, major events leading to increased vascular permeability and pulmonary interstitial edema.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.