bronchi

Bronchi are the main passageways through which air enters the lungs, forming part of the lower respiratory tract. In humans, the trachea divides into the right and left primary bronchi, which enter their respective lungs and progressively branch into smaller bronchi, ultimately supplying the entire pulmonary lobes. The term bronchi is plural; a single passage is a bronchus. The bronchi are lined with mucous membrane and supported by cartilaginous rings and plates, with a progressively decreasing amount of cartilage toward the periphery.

Right main bronchus is wider, shorter, and more vertical than the left, which contributes to a higher incidence of aspirated material entering the right lung. They split into lobar (secondary) bronchi for each lung lobe and then into segmental (tertiary) bronchi, which subdivide further into smaller bronchial branches. Toward the periphery, bronchi lose cartilage support and give way to bronchioles, which lack cartilage and eventually lead to alveolar ducts and sacs involved in gas exchange.

Structure and function: The bronchial tree serves to conduct, warm and humidify inspired air and to filter debris. The bronchial epithelium is typically pseudostratified ciliated columnar with goblet cells, which produce mucus and support ciliary movement that clears particles and pathogens. The submucosa contains glands, and smooth muscle in the walls regulates airway diameter under autonomic control (sympathetic and parasympathetic pathways).

Clinical relevance: Bronchitis refers to inflammation of the bronchi and can be acute or chronic. Chronic bronchitis, asthma, and chronic obstructive pulmonary disease involve bronchial inflammation and narrowing that impair airflow. Infections, irritants such as tobacco smoke, or structural abnormalities can affect the bronchial trees and lead to impaired ventilation.