Q3 LONG ANSWER 10M ★ High-yield

Describe the lungs with their lobes, fissures and root. Explain bronchopulmonary segments and add a note on the pleura.

Anatomy · 1st Professional — Pre-Clinical

Feature	Right lung	Left lung
Lobes	Three — upper, middle, lower	Two — upper, lower
Fissures	Oblique and horizontal	Oblique only
Bronchopulmonary segments	10	8–10
Size	Larger and heavier, but shorter	Smaller, longer and narrower
Special features	Grooves for the azygos vein and SVC	Cardiac notch and lingula

The right lung is shorter because of the liver, and wider because the heart projects to the left

The root is the collection of structures entering and leaving the lung at the hilum, enclosed in a sleeve of pleura.

Arrangement	Right	Left
Anterior to posterior	Superior pulmonary vein, pulmonary artery, bronchus	Superior pulmonary vein, pulmonary artery, bronchus
Superior to inferior	Eparterial bronchus, pulmonary artery, hyparterial bronchus, inferior pulmonary vein	Pulmonary artery, bronchus, inferior pulmonary vein

Only the right lung has an eparterial bronchus — the bronchus to the upper lobe, arising above the level of the artery
Also in the root — bronchial vessels, pulmonary plexuses of nerves, and bronchopulmonary lymph nodes
Anterior relations — phrenic nerve; posterior — vagus. Mnemonic: "phrenic in front"

Trachea bifurcates at the sternal angle (T4/T5) at the carina
Right main bronchus is wider, shorter and more vertical (25° against 45°)
Therefore inhaled foreign bodies and aspirated material pass into the right bronchus, and aspiration pneumonia affects the right lower lobe
Right main bronchus about 2.5 cm long, left about 5 cm

A bronchopulmonary segment is the portion of lung supplied by a segmental (tertiary) bronchus with its own segmental artery.

Pyramidal, apex at the hilum, base at the surface
Structurally and functionally independent, separated by connective tissue septa
Each has its own bronchus and artery, but the veins lie intersegmental — draining adjacent segments, and used as surgical landmarks
Can be resected individually (segmentectomy) — the practical reason the concept matters
Right lung — upper 3, middle 2, lower 5; left — upper 5 (including 2 lingular), lower 5

A serous membrane with two layers — visceral, adherent to the lung, and parietal, lining the thoracic wall
They are continuous at the hilum and below it as the pulmonary ligament
The pleural cavity is a potential space with a thin film of fluid and a negative pressure

Part of parietal pleura	Nerve supply	Sensitivity
Costal	Intercostal nerves	Very sensitive; pain referred to the chest wall
Diaphragmatic — central	Phrenic (C3, C4, C5)	Pain referred to the shoulder tip
Diaphragmatic — peripheral	Lower intercostal nerves	Pain in the chest and abdominal wall
Mediastinal	Phrenic	Shoulder tip
Visceral pleura	Autonomic (pulmonary plexus)	Insensitive to pain

Recess	Position	Significance
Costodiaphragmatic	Between the costal and diaphragmatic pleura	The deepest recess; fluid collects here first — the site of pleural aspiration
Costomediastinal	Anteriorly, especially on the left at the cardiac notch	The lingula enters it on deep inspiration

Lung and pleural borders differ by two ribs — a useful rule:Lung lower border — 6th rib mid-clavicular, 8th mid-axillary, 10th paravertebral
Pleura lower border — 8th, 10th, 12th at the same lines
The apex of the lung and pleura rise 2.5 cm above the medial third of the clavicle — hence vulnerable in supraclavicular procedures

Pleural aspiration (thoracocentesis) is performed in the 7th to 9th intercostal space in the mid-axillary or scapular line, and the needle passed along the upper border of the rib below to avoid the neurovascular bundle
Pneumothorax — air in the pleural cavity abolishes the negative pressure and the lung collapses by its own elastic recoil; a tension pneumothorax shifts the mediastinum and is an emergency, decompressed in the 2nd space mid-clavicular line or the 5th space anterior axillary line
Subclavian vein cannulation and supraclavicular block risk pneumothorax, because the pleural apex rises above the clavicle
Postural drainage depends on segmental anatomy — the patient is positioned so the affected segment drains toward the hilum
Bronchoscopy is guided by segmental anatomy; the carina is the key landmark, and its widening suggests subcarinal nodal disease
Lung abscess characteristically forms in the posterior segment of the right upper lobe or the superior segment of the right lower lobe, the dependent segments in a supine patient
Bronchial and pulmonary circulations are separate — the bronchial arteries from the aorta nourish the lung tissue, while the pulmonary arteries carry deoxygenated blood for gas exchange; this is why a pulmonary embolus does not always infarct the lung
Pancoast tumour at the apex invades the sympathetic chain and lower brachial plexus, giving Horner syndrome and wasting of the small hand muscles

All questions in Thorax