Alveolmembranet

Alveolmembranet is a term that appears occasionally in discussions of pulmonary anatomy, referring to the membrane that forms the barrier between the air-filled alveolar spaces and the blood in the pulmonary capillaries. In mainstream anatomy, this structure is usually called the alveolar membrane or the alveolocapillary membrane, and alveolmembranet is not widely adopted in modern textbooks.

Anatomy and composition: The core barrier is composed of the alveolar epithelium (primarily type I pneumocytes), a fused basement membrane, and the capillary endothelium, with only a very thin interstitial space separating the two. The combined thickness is kept extremely small to facilitate efficient diffusion, typically on the order of a few hundred nanometers in healthy lungs. Surfactant coats the alveolar surface, reducing surface tension and helping maintain alveolar stability.

Function: The alveolmembranet enables gas exchange, allowing oxygen to move from the alveolar air into the blood and carbon dioxide to move in the opposite direction. It also plays a role in fluid regulation and host defense, supported by alveolar macrophages that patrol the airspaces.

Clinical relevance: Impairment or thickening of this barrier—due to edema, fibrosis, inflammation, or other lung diseases—reduces gas diffusion and can lead to hypoxemia. Conditions such as acute respiratory distress syndrome and interstitial lung disease illustrate how barrier integrity affects respiratory function. Diffusing capacity tests (DLCO) assess the performance of this barrier.

Etymology and usage: The term alveolmembranet is rare and largely synonymous with the alveolar or alveolocapillary membrane in many sources. See also alveolar-capillary membrane; alveolocapillary barrier.