pulmonary capillary
Summary
Pulmonary capillaries are the microscopic blood vessels in the lungs where gas exchange occurs between alveolar air and blood. They form an extensive network around alveoli, with walls so thin (0.5 micrometers) that they allow rapid diffusion of oxygen and carbon dioxide. The pulmonary capillary wedge pressure (PCWP) is a key hemodynamic measurement reflecting left atrial pressure.
Detail
Pulmonary capillaries are single-cell-thick endothelial vessels that surround each alveolus, creating the respiratory membrane where gas exchange occurs. The capillary network is so dense that it forms an almost continuous sheet of blood around each alveolus. The respiratory membrane consists of three layers: alveolar epithelium, shared basement membrane, and capillary endothelium, with a total thickness of only 0.5 micrometers. This extreme thinness facilitates rapid gas diffusion according to Fick's law. Pulmonary capillaries receive deoxygenated blood from pulmonary arterioles and deliver oxygenated blood to pulmonary venules. Clinically, pulmonary capillary wedge pressure (measured via Swan-Ganz catheter) reflects left atrial pressure and is used to assess left heart function and diagnose conditions like heart failure, mitral stenosis, and pulmonary edema. Normal PCWP is 6-12 mmHg; elevated values (>18 mmHg) suggest left heart dysfunction or fluid overload.
Sources
- Guyton and Hall Textbook of Medical Physiology
- West's Respiratory Physiology
- Braunwald's Heart Disease
- First Aid for USMLE Step 1
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