M01.05.020 Lungs

The lungs are essential organs responsible for respiration, located in the thoracic cavity, and play a key role in oxygenating blood. This article covers their anatomy, neurovascular supply, and clinical relevance.

Table of Contents

1. Anatomical Position and Relations
2. Lung Structure
3. Lung Lobes and Fissures
4. Surfaces and Borders
5. Root and Hilum
6. Bronchial Tree
7. Vasculature
8. Nerve Supply
9. Lymphatic Drainage
10. Clinical Relevance

• Pulmonary Embolism

1. Anatomical Position and Relations

The lungs are located on either side of the mediastinum, within the thoracic cavity. They are suspended from the mediastinum by the lung root, a collection of structures that enter and leave the lungs.

The lungs are enclosed by pleural cavities formed by the visceral and parietal pleura.

2. Lung Structure

The lungs are roughly cone-shaped with three primary anatomical features:

• Apex: The superior, blunt end of the lung, projecting above the first rib.
• Base: The inferior surface that rests on the diaphragm.
• Lobes: The right lung has three lobes, while the left lung has two.

Each lung has:

• Three surfaces: Costal, mediastinal, and diaphragmatic.
• Three borders: Anterior, inferior, and posterior.

3. Lung Lobes and Fissures

Right Lung

• Lobes: Superior, middle, and inferior
• Fissures:
  • Oblique fissure
  • Horizontal fissure

Left Lung

• Lobes: Superior and inferior
• Fissures:
  • Oblique fissure (similar to right lung)

4. Surfaces and Borders

Surfaces

• Mediastinal Surface: Faces the mediastinum and contains the lung Hilum.
• Diaphragmatic Surface: Forms the base of the lung and rests on the diaphragm.
• Costal Surface: Faces the chest wall and is separated from ribs by the costal pleura.

Borders

• Anterior Border: Converges the costal and mediastinal surfaces, with a cardiac notch on the left lung.
• Inferior Border: Separates the lung base from other surfaces.
• Posterior Border: Smooth and rounded, contrasting with the sharp anterior and inferior borders.

5. Root and Hilum

The lung root consists of structures entering and leaving the lung at the Hilum:

• Bronchus
• Pulmonary artery
• Pulmonary veins
• Bronchial vessels
• Pulmonary plexus of nerves
• Lymphatic vessels

These structures pass through the hilum, which is located on the mediastinal surface of the lung.

6. Bronchial Tree

The bronchial tree begins with the trachea, dividing into:

1. Left and right bronchi
2. Lobar bronchi (one for each lobe)
3. Segmental bronchi (supply bronchopulmonary segments)

From Segmental bronchi, air passes into conducting bronchioles, eventually reaching respiratory bronchioles and alveoli, where gas exchange occurs.

7. Vasculature

Pulmonary Circulation:

• Pulmonary Arteries: Supply deoxygenated blood to the lungs.
• Pulmonary Veins: Carry oxygenated blood to the heart.

Bronchial Circulation:

• Bronchial Arteries: Supply the bronchi, lung roots, and pleura.
• Bronchial Veins: Drain into the Azygos and hemiazygos veins.

8. Nerve Supply

The lungs are innervated by the pulmonary plexuses:

• Parasympathetic: Derived from the vagus nerve (stimulates bronchoconstriction, and secretion).
• Sympathetic: Derived from sympathetic trunks (stimulates bronchodilation, and vasoconstriction).
• Visceral Afferent: Carries pain impulses to the vagus nerve ganglia.

9. Lymphatic Drainage

Lymphatic vessels of the lungs arise from:

• Superficial Plexus: Drains lung parenchyma.
• Deep Plexus: Drains lung root structures.

Both plexuses drain into the tracheobronchial nodes and eventually into the bronchomediastinal trunks.

10. Clinical Relevance

Pulmonary Embolism

Pulmonary embolism occurs when a substance obstructs the pulmonary artery. Common causes include:

• Thrombus: Most common, usually from deep vein thrombosis.
• Fat Embolism: From bone fractures.
• Air Embolism: From medical procedures.

Symptoms:

• Dyspnoea, chest pain, cough, hemoptysis, tachypnoea.

Management:

• Anticoagulation and thrombolytic therapy to reduce embolus size and prevent further clotting.

Points to Remember

• The lungs are located in the thoracic cavity, surrounded by pleural cavities.
• The right lung has three lobes; the left lung has two due to the position of the heart.
• The Hilum is a critical structure where all lung vessels and airways pass.
• The lungs receive deoxygenated blood via pulmonary arteries and oxygenated blood through pulmonary veins.
• Clinical conditions like pulmonary embolism can significantly affect lung function.