Alveolarwand

The alveolar wall, or alveolar septum, is the thin structural boundary that forms the walls of the tiny air sacs (alveoli) in the lungs. It constitutes the principal gas-exchange surface where air in the alveoli meets blood in the surrounding capillaries.

Anatomy and components: The wall is made up mainly of the alveolar epithelium, consisting of type I pneumocytes that cover most of the surface and type II pneumocytes that secrete surfactant. A shared basement membrane lies between the epithelium and the capillary endothelium, which forms the other half of the barrier. Interstitial connective tissue containing collagen and elastic fibers provides structural support. Alveolar walls may also house alveolar macrophages on the surface and are linked by small pores of Kohn that allow collateral ventilation.

Function: The alveolar wall is designed to be extremely thin to minimize diffusion distance for oxygen and carbon dioxide. Type II cells contribute to surfactant production, reducing surface tension and helping to keep alveoli open. The capillary network within the wall enables efficient gas transfer and participates in immune defense.

Clinical relevance: Thickening, edema, inflammation, or fibrosis of the alveolar wall can impede gas exchange and contribute to respiratory failure. Conditions such as acute respiratory distress syndrome, interstitial lung disease, and pulmonary edema involve alterations of the alveolar wall, affecting diffusion capacity and lung mechanics.

Development: Alveolar walls form and mature mainly after birth, with ongoing remodeling during early life. Disruptions in development can influence long-term pulmonary function.