Learning Objective

Understand the anatomy of the lungs, including lobes, surfaces, borders, root structures, bronchial tree, vasculature, nerve supply, and recognize their clinical relevance.

The lungs are the organs of respiration, located in the thorax on either side of the mediastinum. Their function is to oxygenate blood by bringing inspired air into contact with oxygen-poor blood in the pulmonary capillaries.

This lesson covers the anatomical relations, neurovascular supply, and clinical correlations of the lungs. The trachea, bronchi, and bronchioles are covered separately.

Anatomical Position and Relations

The lungs lie on either side of the mediastinum within the thoracic cavity, each surrounded by a pleural cavity. They are suspended from the mediastinum by the lung root, which contains structures entering and leaving the lungs.

Medial surfaces relate to:

Left Lung: Heart, Arch of aorta, Thoracic aorta, Oesophagus
Right Lung: Heart, Oesophagus, Inferior vena cava, Superior vena cava, Azygous vein

Lung Structure

The lungs are roughly cone-shaped with an apex, base, three surfaces, and three borders. The left lung is slightly smaller due to the presence of the heart.

Each lung has:

Apex: superior end projecting above the 1st rib
Base: the inferior surface of the diaphragm
Lobes: separated by fissures
Surfaces: costal, mediastinal, diaphragmatic
Borders: anterior, inferior, posterior

Lobes and Fissures

The right lung has three lobes (superior, middle, and inferior) divided by the oblique and horizontal fissures. The left lung has two lobes (superior, inferior) separated by an oblique fissure.

Surfaces

Costal surface faces the chest wall, diaphragmatic surface rests on the diaphragm, and mediastinal surface contains the hilum where structures enter and leave the lung.

Activity

Borders

The anterior border contains the cardiac notch on the left. The inferior border separates the base from the costal/mediastinal surfaces, posterior border is smooth and rounded.

Root and Hilum

The lung root contains the bronchus, pulmonary artery, two pulmonary veins, bronchial vessels, pulmonary plexus, and lymphatics. All enter via the hilum.

Bronchial Tree

The trachea divides into left and right bronchi. Bronchi branch into lobar and segmental bronchi, supplying bronchopulmonary segments. Terminal bronchioles lead to alveoli, the site of gas exchange.

Vasculature

The lungs receive deoxygenated blood via pulmonary arteries and return oxygenated blood via pulmonary veins. Bronchial arteries provide a nutritive supply. Bronchial veins drain into the azygos and accessory hemiazygos veins.

Activity

Nerve Supply

The pulmonary plexus contains:

Parasympathetic fibers (vagus nerve) – bronchial gland secretion, bronchial smooth muscle contraction, vasodilation
Sympathetic fibers – bronchial smooth muscle relaxation, vasoconstriction
Visceral afferents – pain impulses to vagus sensory ganglia

Lymphatic Drainage

Two plexuses: superficial (subpleural) and deep, draining into tracheobronchial nodes and then into bronchomediastinal trunks.

Activity

Clinical Relevance: Pulmonary Embolism

A pulmonary embolism is an obstruction of a pulmonary artery by thrombus, fat, or air. It reduces lung perfusion, decreases blood oxygenation, and increases right ventricular pressure. Symptoms include dyspnea, chest pain, cough, hemoptysis, and tachypnea. Assessment can use the Wells’ score. Treatment involves anticoagulation and thrombolytic therapy.