Lung Anatomy

Understanding lung anatomy is fundamental for interpreting chest X-rays, performing auscultation, and managing common respiratory conditions like pneumonia, pneumothorax, and lung cancer. You'll need to know the lobar and segmental anatomy for localising pathology, and the pleural reflections for understanding effusions and pneumothoraces. This knowledge is high-yield for both SBA questions and OSCEs.

The tracheobronchial tree begins with the trachea, anterior to the oesophagus, supported by C-shaped cartilage rings. Its bifurcation at the carina is a key anatomical landmark. The main bronchi divide into lobar (secondary) bronchi, then segmental (tertiary) bronchi, supplying the bronchopulmonary segments. These segments are clinically important as they are functionally independent units, allowing for targeted surgical resection (e.g., for lung cancer). The pulmonary circulation, distinct from the systemic circulation, facilitates gas exchange. Bronchial arteries (from the aorta) supply oxygenated blood to the lung tissue itself. Lymphatic drainage follows the bronchi, progressing from intrapulmonary nodes to hilar, tracheobronchial, and paratracheal nodes – crucial for cancer staging. Nerve supply is via the pulmonary plexus: parasympathetic (vagus) causes bronchoconstriction and secretomotor, while sympathetic causes bronchodilation.

Aspiration pneumonia frequently affects the right lower lobe due to the anatomical orientation of the right main bronchus. Pneumothorax (air in the pleural space) can lead to lung collapse; a tension pneumothorax is a life-threatening emergency causing mediastinal shift and haemodynamic compromise. Pleural effusions (fluid in the pleural space) often accumulate in the costodiaphragmatic recesses, visible on CXR. Pancoast tumours (apical lung tumours) can invade the brachial plexus (causing T1 palsy/hand weakness) or the sympathetic chain (leading to Horner's syndrome: ptosis, miosis, anhidrosis). Understanding the location of fissures is vital for interpreting chest X-rays, differentiating lobar pneumonia from pleural effusions, and localising pathology.

Chest X-ray (CXR): Essential initial imaging. Look for lobar consolidation (pneumonia), pleural effusions (blunting of costophrenic angles), pneumothorax (absence of lung markings, visceral pleural line), or masses. Recognise the silhouette sign (loss of border between lung and adjacent structure due to consolidation). CT Chest: Provides detailed anatomical information, crucial for characterising masses, staging lung cancer (TNM), and assessing complex pleural disease. Bronchoscopy: Direct visualisation of the tracheobronchial tree, allowing for biopsy and therapeutic interventions. Spirometry: Assesses lung function, not anatomy, but is a key investigation for respiratory disease.

Management often involves medical therapies like bronchodilators (asthma, COPD), antibiotics (pneumonia), or chemotherapy/radiotherapy for malignancy. Surgical interventions include lobectomy or segmentectomy for lung cancer. For a tension pneumothorax, immediate needle decompression (2nd intercostal space, midclavicular line) followed by chest drain insertion (safe triangle: 5th intercostal space, mid-axillary line) is life-saving. Understanding the 'safe triangle' for chest drain insertion (anterior border of latissimus dorsi, lateral border of pectoralis major, apex at axilla, base at 5th intercostal space) is an OSCE favourite.