Alveolar-capillary membrane (ACM)

The alveolar-capillary membrane, often referred to as the blood-gas barrier, is a specialized physiological structure in the lungs where gas exchange occurs between the alveolar air and the pulmonary capillary blood (StatPearls, 2023). It is composed of three primary layers: the alveolar epithelium (Type I and Type II pneumocytes), a shared basement membrane, and the capillary endothelium (NIH, 2022). This extremely thin barrier, measuring roughly 0.2 to 0.6 micrometers, facilitates the rapid diffusion of oxygen into the blood and carbon dioxide into the alveoli while preventing the leakage of plasma into the air spaces (West, 2003). In clinical conditions such as Acute Respiratory Distress Syndrome (ARDS), pneumonia, and pulmonary edema, the membrane's integrity is disrupted, leading to fluid accumulation and severely impaired gas exchange (PubMed, 2021). While the membrane itself is a multi-component tissue structure rather than a single molecular target, it serves as the site of action for various therapies, including exogenous surfactants to reduce surface tension and inhaled vasodilators to improve perfusion (PubChem, 2024).

Other names

Blood-gas barrierAlveolar-capillary barrierRespiratory membraneBlood-air barrier

Reduction of alveolar surface tension, pulmonary vasodilation, and modulation of epithelial/endothelial permeability (StatPearls, 2023).