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Structure

Lungs

Not medically reviewed · Content last updated · 2 min read ·

This is the date the draft was written, not a medical review date.

The lungs are the paired organs of gas exchange, each enclosed in its own pleural sac and lying on either side of the mediastinum. The right lung has three lobes and the left has two.

Terminologia Anatomica (Latin): Pulmones · Open in the 3D atlas

Location

Each lung occupies a pleural cavity within the thoracic cage. The apex projects above the first rib into the root of the neck, and the base rests on the diaphragm. Costal, mediastinal and diaphragmatic surfaces are described.

Structure

The right lung has upper, middle and lower lobes separated by oblique and horizontal fissures. The left lung has upper and lower lobes separated by an oblique fissure; its upper lobe bears the cardiac notch and the lingula. Each lung is divided into bronchopulmonary segments: 10 on the right, while the left is usually described as 8 to 10 depending on the numbering convention. The hilum transmits the principal bronchus, pulmonary artery, pulmonary veins, bronchial vessels, nerves and lymphatics.

Blood supply

The pulmonary arteries carry deoxygenated blood to the alveolar capillaries, and usually two pulmonary veins per lung return oxygenated blood to the left atrium. The lung tissue itself is nourished by bronchial arteries from the thoracic aorta or intercostal arteries; bronchial veins drain partly to the azygos system and partly to the pulmonary veins.

Innervation

Anterior and posterior pulmonary plexuses at the lung root carry vagal parasympathetic fibres (bronchoconstriction, glandular secretion) and sympathetic fibres from the upper thoracic segments (bronchodilation). The visceral pleura has no pain fibres, whereas the parietal pleura is pain-sensitive through the intercostal and phrenic nerves.

Function

The lungs bring inspired air into close contact with pulmonary capillary blood across the thin alveolar-capillary membrane, allowing oxygen uptake and carbon dioxide elimination. They also contribute to acid-base balance, filtration of small emboli and metabolic functions such as angiotensin I conversion.

Clinical correlations

Pneumothorax and pleural effusion alter the pleural space and are assessed clinically and by imaging. Aspirated material tends to enter the right lung because of the more vertical right main bronchus, and segmental anatomy guides bronchoscopy, resection and interpretation of lobar collapse. Lung cancer and pulmonary embolism are common serious conditions.

Common exam points

  • Right lung: 3 lobes, 2 fissures (oblique and horizontal); left lung: 2 lobes, 1 oblique fissure, with cardiac notch and lingula.
  • Right lung has 10 bronchopulmonary segments; left is usually 8 to 10, depending on the numbering convention.
  • Hilum contents: principal bronchus, pulmonary artery, two pulmonary veins, bronchial vessels, nerves, lymphatics.
  • Dual supply: pulmonary circulation for gas exchange, bronchial arteries for nutrition of the lung tissue.
  • Visceral pleura is insensitive to pain; parietal pleura is sensitive (intercostal and phrenic nerves).

References

  1. Drake RL, Vogl AW, Mitchell AWM. Gray's Anatomy for Students. Elsevier — Tier 3 (textbook)
  2. Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy. Wolters Kluwer, 8th edition (2018) — Tier 3 (textbook)
  3. Murray and Nadel's Textbook of Respiratory Medicine. Elsevier, 7th edition (2021) — Tier 3 (textbook)

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