interalveolar septum

The interalveolar septum is the wall that separates two adjacent alveoli, which are tiny air sacs in the lungs where gas exchange occurs. These septa are crucial for the respiratory system as they form the air-blood barrier, allowing oxygen to enter the blood and carbon dioxide to leave it through diffusion.12

The septum is composed of a dense network of capillaries, the smallest blood vessels, supported by a framework of connective tissue fibers, including collagen and elastic fibers. This structure is lined on both sides by epithelial cells, primarily Type I pneumocytes, which form the thin barrier necessary for efficient gas exchange. Type II pneumocytes, also present, secrete pulmonary surfactant, a substance that reduces surface tension and prevents the alveoli from collapsing. Alveolar macrophages also reside on the surface, acting as scavengers to keep the air spaces clean.12