lowerrespiratory

Lower respiratory, or the lower respiratory tract, refers to the portion of the respiratory system that conducts air from the trachea to the gas-exchanging units of the lung. It includes the trachea, the main bronchi, their divisions into smaller bronchi and bronchioles, and the alveoli where gas exchange occurs. The upper respiratory tract comprises the nasal passages, pharynx, and larynx. The lower tract primarily handles air conduction, humidification, and gas exchange.

Anatomy and physiology: The tracheobronchial tree branches to maximize surface area for gas exchange. Lungs contain alveoli with a thin barrier and are served by the pulmonary circulation. The airway walls have smooth muscle and mucous glands. The mucociliary escalator and alveolar macrophages defend against inhaled pathogens. Gas exchange depends on ventilation–perfusion matching and alveolar integrity.

Clinical relevance: The lower tract is affected by infections such as pneumonia and bronchiolitis, as well as chronic diseases including asthma and COPD, bronchiectasis, and ARDS. Diagnosis uses history, examination, chest imaging, and pulmonary function tests; bronchoscopy may be used for visualization. Treatments vary by condition and may include antibiotics for infections, bronchodilators and steroids for airway disease, and supplemental oxygen. Vaccines against influenza and pneumococcus reduce risk of many lower respiratory infections.