Lungs

About the Lungs

The lungs are paired organs in the thoracic cavity separated by the mediastinum. The right lung has three lobes upper, middle, lower and the left lung has two lobes upper and lower plus the cardiac notch to accommodate the heart. Total lung capacity is approximately 6 liters in adults. Gas exchange occurs in approximately 300 to 500 million alveoli, providing 70 square meters of surface area roughly half a tennis court. The trachea divides into right and left main bronchi, then lobar bronchi, segmental bronchi, and terminal bronchioles, totaling 23 generations of branching the tracheobronchial tree. Type I pneumocytes form the thin gas exchange barrier with capillaries. Type II pneumocytes produce surfactant, reducing alveolar surface tension and preventing collapse atelectasis. Breathing is driven by the diaphragm primary muscle, contracting 12 to 20 times per minute at rest, and external intercostal muscles. The pleura visceral and parietal with pleural fluid provides friction free movement and negative pressure maintaining lung inflation.