Bronhiolelor

Bronhiolelor (bronchioles) are the small airways of the lungs that conduct air from the larger bronchi to the gas-exchanging zones. They measure about 0.5 millimeters or less in diameter and branch from the tertiary bronchi into a network of conducting bronchioles and, distally, respiratory bronchioles. The terminal bronchioles form the end of the conducting airways, while the respiratory bronchioles bear alveoli along their walls and participate in gas exchange.

Two main subtypes are recognized: terminal bronchioles, which lack alveoli and glands and rely on smooth muscle for regulation, and respiratory bronchioles, which have alveoli along their walls and contribute to gas exchange.

Histology changes along the bronchiolar tree. Proximal bronchioles are lined by ciliated epithelium that diminishes in height toward the distal sections; club cells increase in abundance in the terminal bronchioles. Cartilage and large glands are absent from bronchioles; smooth muscle is more prominent, allowing bronchomotor control by the autonomic nervous system and local mediators.

Functionally, bronhiolelor regulate airflow and airway resistance. They are subject to autonomic control: sympathetic stimulation via beta-2 receptors dilates bronchioles, while parasympathetic activity and irritants cause constriction. Mucociliary clearance helps remove debris and pathogens.

Clinically, bronchiolitis is inflammation of the bronchioles and is common in infants, often caused by viral infections such as RSV. In chronic disease, bronchioles can undergo remodeling in asthma and small-airways disease in COPD, leading to airflow limitation. Understanding bronchioles clarifies mechanisms of obstructive lung diseases and their treatment.