Alveolele

Alveolele is the Romanian definite plural form of "alveolă" and commonly refers to the microscopic air sacs in the lungs known in English as alveoli. Alveoli are terminal structures of the respiratory tree where the blood–air barrier allows exchange of oxygen and carbon dioxide between inspired air and the pulmonary circulation. Each human lung contains millions of alveoli, which collectively provide a very large surface area relative to body size.

Structurally, an alveolus is lined by a thin epithelium composed mainly of two cell types: squamous type I pneumocytes that form the gas-permeable surface, and cuboidal type II pneumocytes that secrete pulmonary surfactant and serve as progenitor cells for the epithelium. Capillaries closely appose the alveolar walls, and alveolar macrophages patrol the airspaces to remove particulates and pathogens. The surfactant reduces surface tension, preventing alveolar collapse during exhalation.

Functionally, alveoli enable efficient diffusion of respiratory gases driven by partial pressure gradients. Their integrity and patency are essential for adequate oxygenation and removal of carbon dioxide. Alveolar damage or inflammation is central to many pulmonary diseases, including emphysema (loss of alveolar walls), pneumonia (infection and filling of airspaces), and acute respiratory distress syndrome (disruption of the alveolar–capillary barrier). Clinical assessment of alveolar function uses imaging, blood gas analysis, and pulmonary function tests. Development, maintenance, and repair of alveolar structures are active areas of research with implications for treating chronic and acute lung disorders.