Alveolemembraner

Alveolemembraner, often translated as alveolar membranes, refer to the thin barriers that separate the air in the pulmonary alveoli from the blood in the surrounding capillaries. These membranes form the alveolar-capillary barrier, the primary site of gas exchange in the lungs.

Anatomy and components: The barrier consists of the alveolar epithelium (primarily type I pneumocytes covering most of the surface and type II pneumocytes that produce surfactant and serve as progenitors), a fused basement membrane of epithelial and endothelial origin, the capillary endothelium, and the intervening interstitial space with occasional alveolar macrophages. The total surface area is large, roughly 70–100 square meters in an adult, and the barrier is extremely thin, about 0.2–0.6 micrometers.

Function: The thin barrier enables diffusion of oxygen from the air into the blood and carbon dioxide from the blood into the air. Surfactant produced by type II cells reduces surface tension to prevent alveolar collapse and to stabilize the alveoli during breathing. Alveolar macrophages patrol the surfaces to clear inhaled particles and pathogens.

Clinical relevance: Injury or thickening of the alveolar membranes occurs in conditions such as acute respiratory distress syndrome, pulmonary edema, and interstitial lung diseases, impairing gas exchange and causing hypoxemia. Measurements like diffusion capacity for carbon monoxide (DLCO) assess barrier integrity, while imaging may reveal edema or interstitial thickening.

Terminology and research: In Norwegian or Swedish contexts, alveolemembraner denotes this structure. Research continues on alveolar-capillary barrier remodeling during development, injury, and repair.