Lungs

The lungs are a pair of spongy, air-filled organs located in the thoracic cavity. The right lung contains three lobes; the left lung contains two, and the cardiac notch on the left accommodates the heart. Each lung is enclosed by a double-layered pleural membrane with pleural fluid in between. The lungs extend from the apex near the collarbone to the base above the diaphragm.

The primary function is gas exchange. Airways begin with the trachea, branch into bronchi, then bronchioles, terminating in alveolar sacs. Alveoli are microscopic air sacs where oxygen diffuses into pulmonary capillaries and carbon dioxide diffuses in the opposite direction. The alveolar-capillary barrier and large surface area support efficient diffusion.

Blood supply and ventilation: Pulmonary circulation carries deoxygenated blood from the right ventricle to the lungs and returns oxygenated blood to the left atrium. Bronchial arteries provide systemic oxygen to lung tissue. Ventilation is driven by the diaphragm and intercostal muscles; inhalation expands the thoracic cavity, exhalation is typically passive. Gas transport in blood involves hemoglobin.

Clinical notes: Common diseases include pneumonia, chronic obstructive pulmonary disease, asthma, lung cancer, and interstitial lung disease. Diagnosis uses imaging (chest X-ray, CT) and functional tests (spirometry, DLCO). Treatments focus on relieving symptoms, infection control, and prevention through vaccination and smoking cessation; acute care may involve supplemental oxygen or mechanical ventilation.