Alveoli, Anatomy

Description

Pulmonary alveoli fill the field as clusters of small, thin walled air sacs at the terminal portions of the respiratory tree, continuous with alveolar ducts and separated by delicate interalveolar septa. A dense capillary network closely invests the outer surface of each alveolus, with capillary loops running along the septa so the airspace remains immediately adjacent to blood. The alveolar wall is implied as a layered interface, where type I pneumocytes form most of the luminal lining, type II pneumocytes sit at septal angles as surfactant producing cells, and alveolar macrophages may be present within the airspace. Gas exchange happens here. Clinical teaching often hinges on the geometry of this blood gas barrier: alveolar epithelium, fused basal laminae, and capillary endothelium arranged in microns, so any increase in diffusion distance or loss of surface area shows up quickly as hypoxemia. Pulmonary edema, acute respiratory distress syndrome (diffuse alveolar damage), and interstitial fibrosis all thicken or flood the septa, while emphysema reduces septal tissue and capillary bed, a structural explanation for reduced diffusing capacity (DLCO). The fixed close range perspective helps you point to where ventilation meets perfusion, and why a small change at the septum has system level consequences. Respiratory physiology lectures and histology labs can pair this illustration with spirometry, DLCO interpretation, and the alveolar gas equation to connect structure to numbers. It also fits pulmonary and critical care publications discussing edema fluid in the alveolus, surfactant dysfunction in neonatal respiratory distress syndrome, or microvascular injury in ARDS. Anatomical accuracy verified by SciePro's Medical Advisory Board.