The Lungs

Pleurae and pleural cavities | Main Anatomy Index | Blood vessels and nerves of the lungs

Last updated 30 March 2006

The Lungs

• The lungs (L. pulmones) are the essential organs of respiration.
• Their main function is to oxygenate the mixed venous blood.

• Each lung is conical in shape and is contained in its own pleural sac.
• The lungs are separated from each other by the heart and great vessels in the middle mediastinum.

• The lungs are attached to the heart and trachea by the structures in the root of the lungs and to the pericardium by the pulmonary ligaments.

• The hardened lungs in an embalmed cadaver have surface impressions, which were formed by the structures adjacent to them.
• These markings provide clues to the relationships of the lungs, but they are not visible during surgery or in fresh post-mortem specimens.
• Each lung has an apex, base, and hilum (hilus).

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The Apex of the Lung

• The rounded, tapered superior end or apex of the lung extends through the superior thoracic aperture into the root of the neck.
• Here, it lies in close contact to the dome or the cupula of the pleura.

• The apex of the lung is crossed by the subclavian artery, which produces a groove in the mediastinal surface.
• The artery, however, is separated from the cupula by the suprapleural membrane.

The Base of the Lung

• This is the concave diaphragmatic surface of the lung, which is related to the dome of the diaphragm.
• The base of the right lung is deeper because the right dome rises to a more superior level.
• Its inferior border is thin and sharp where it enters the costodiaphragmatic recess.

The Root of the Lung

• The root serves as the attachment of the lung and is the "highway" for the transmission of the structures entering and leaving the lung at the hilum.
• It connects the medial surface of the lung to the heart and trachea and is surrounded by the reflection of parietal to visceral pleura.

The Hilum of the Lung

• This is the where the root is attached to the lung.
• It contains the main bronchus, pulmonary vessels (one artery and two veins), bronchial vessels, lymph vessels, and nerves entering and leaving the lung.

The Main Differences Between the Right and Left Lungs

• The right lung has 3 lobes while the left has 2 lobes.
• The right lung is larger and heavier than the left lung, but is shorter and wider because the right dome of the diaphragm is higher and the heart and pericardium bulge more to the left.

• The anterior margin of the right lung is straight, whereas the margin of the left lung has a deep cardiac notch.

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Lobes and Fissures of the Lungs

The Left Lung

• This is divided into superior (upper) and inferior (lower) lobes by a long deep oblique fissure.
• This extends from its costal to its medial surface.

• The superior lobe has a large cardiac notch on its anterior border, where the lung is deficient owing to the bulge of the heart.

• The anteroinferior part of the superior lobe has a small tongue-like projection called the lingula.

• The inferior lobe of the left lung is larger than the superior lobe and lies inferoposterior to the oblique fissure.

The Right Lung

• This is divided into superior (upper), middle, and inferior (lower) lobes by horizontal and oblique fissures.
• The horizontal fissure separates the superior and middle lobes.
• The oblique fissure separates the inferior lobe from the superior and middle lobes.

• The superior lobe is smaller than in the left lung, and the middle lobe is wedge-shaped.

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Surfaces of the Lung

The Costal Surface of the Lung

• This surface is large, smooth, and convex.
• It is related to the costal pleura, which separates it from the ribs, their costal cartilages, and the innermost intercostal muscles.
• The posterior part of this surface is related to the thoracic vertebrae.

The Mediastinal Surface

• This medial surface is concave because it is related to the middle mediastinum.
• Because 2/3 of the heart is to the left, the pericardial concavity is deeper in the left lung.
• The mediastinal surface of the embalmed lung shows a cardiac impression produced by the heart and the great vessels.

• This surface also contains the root of the lung, around which the pleura forms a "sleeve" or covering.
• The pulmonary ligament hangs inferiorly from the pleural sleeve around the root of the lung.

The Diaphragmatic Surface

• This is a deeply concave surface, often referred to as the base of the lung.
• It rests on the convex dome of the diaphragm.

• The concavity is deeper in the right lung because of the higher position of the dome.
• Laterally and posteriorly, the diaphragmatic surface is bound by a thin sharp margin that projects into the costodiaphragmatic recess.

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Borders of the Lungs

The Anterior Border of the Lung

• This border is thin and sharp and overlaps the pericardium.
• There is an indentation in the anterior border of the left lung (cardiac notch).

• In each lung, the anterior border separates the costal surface from the mediastinal surface.

• During deep inspiration, the lung projects into the costomediastinal recess of the pleura.

The Posterior Border of the Lung

• This border is broad and rounded and lies in the deep concavity at the side of the thoracic region of the vertebral column, called the paravertebral gutter.

The Inferior Border of the Lung

• This border circumscribes the diaphragmatic surface from the costal surface.
• It is thin and sharp where it projects into the costodiaphragmatic recess.
• It is, however, blunt and rounded medially, where it separates the diaphragmatic surface from the mediastinal surface.

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Surface Markings of the Lungs

Apex of the Lung

• This is represented by a line drawn superolaterally from the sternoclavicular joint to a point 2.5 cm superior to the medial 1/3 of the clavicle and then inferolaterally to the junction of the middle and lateral thirds of the clavicle.

Anterior Border of the Right Lung

• This corresponds to the anterior border of the right pleura.
• Between the level of the 2^nd and 4^th cartilages, its anterior border is near the median plane.
• Inferior to the 4^th costal cartilage, the surface of the right lung gradually diverges from this plane and leaves the sternum posterior to the 6^th costal cartilage.

The Anterior Border of the Left Lung

• This corresponds to the anterior border of the left pleura as far as the level of the 4^th costal cartilage.
• Here, the anterior border deviates laterally to a point about 2.5 cm lateral to the left edge of the sternum to form the cardiac notch.
• It then turns inferiorly and slightly medially to the 6^th costal cartilage.

The Inferior Borders of the Lungs

• These are indicated by a line drawn from the inferior end of the line representing the anterior border that crosses the 6^th rib at the midclavicular line, the 8^th rib in the midaxillary line and the 10^th rib in the midscapular line.

• These borders end about 2.5 cm lateral to the spinous process of T10 vertebra.
• They lie two ribs superior to the pleura on each of three vertical lines just mentioned.

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The Bronchi, Roots, and Bronchopulmonary Segments of the Lungs

• The principal or main bronchus, one for each lung, passes inferolaterally from the bifurcation of the trachea.
• The bronchus accompanies the pulmonary artery into the wedge-shaped hilum of the lung, where it subdivides.

• The right main bronchus is wider, shorter and more vertical (significant in inhaled obstructions) than the left one.
• It is about 2.5 cm long and passes directly into the root of the lung.

• The left main bronchus is about 5 cm long and passes inferolaterally, inferior to the arch of aorta, and anterior to the oesophagus and the descending thoracic aorta.

• Within each lung, the bronchi divide in a constant fashion and in constant directions so that each branch supplies a clearly defined sector of the lung.
• Each main bronchus divides into secondary or lobar bronchi (two for left, three for right), each of which supplies a lobe of the lung.

• Each lobar bronchus divides into tertiary or segmental bronchi, which supply specific segments of the lung, called bronchopulmonary segments.

Left Lung

Superior (upper) lobe:

• Apical
• Posterior
• Anterior
• Superior lingular
• Inferior lingular

Inferior (lower) lobe:

• Superior (apical)
• Medial basal
• Anterior basal
• Lateral basal
• Posterior basal

Right Lung

Superior (upper) lobe:

• Apical
• Posterior
• Anterior

Middle lobe

• Lateral
• Medial

Inferior (lower) lobe:

• Superior (apical)
• Medial basal
• Anterior basal
• Lateral basal
• Posterior basal

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