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Structure

Bronchial tree

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

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

The bronchial tree is the branching system of airways that extends from the main bronchi to the terminal bronchioles. It divides repeatedly, with the conducting zone leading to the respiratory zone where gas exchange occurs.

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

Location

The main bronchi arise at the carina and enter the lung roots at the hila; the branches then ramify inside each lobe and bronchopulmonary segment. The right main bronchus is shorter, wider and more vertical than the left.

Structure

Branching proceeds from main bronchi (right about 2.5 cm, left about 5 cm) to lobar bronchi (3 right, 2 left), segmental bronchi, then bronchioles, terminal bronchioles, respiratory bronchioles, alveolar ducts and alveolar sacs; about 23 generations are described. Cartilage plates and mucous glands disappear at the bronchiolar level, where walls rely on smooth muscle and elastic recoil.

Blood supply

Bronchial arteries (usually from the thoracic aorta) supply the walls of the bronchi down to the respiratory bronchioles, while the alveolar region depends on the pulmonary circulation. Bronchial veins drain to the azygos and hemiazygos systems and to the pulmonary veins.

Innervation

Vagal parasympathetic fibres cause bronchoconstriction and glandular secretion, while sympathetic fibres from upper thoracic segments cause bronchodilation. Cough and irritant afferents run in the vagus nerve.

Function

The conducting airways deliver, warm, humidify and filter inspired air without taking part in gas exchange (anatomical dead space). Smooth muscle tone in the bronchioles regulates airway resistance, and the respiratory zone provides the surface for gas exchange.

Clinical correlations

Bronchoconstriction and mucosal inflammation underlie asthma, and airway obstruction and mucus plugging contribute to chronic obstructive pulmonary disease. Bronchiectasis, aspiration and tumours are other common problems. Bronchoscopy allows direct inspection down to segmental bronchi.

Common exam points

  • Right main bronchus: shorter, wider, more vertical; left main bronchus: longer (about 5 cm), narrower, passes below the aortic arch.
  • Lobar bronchi: 3 on the right, 2 on the left; then segmental bronchi.
  • Conducting zone (to terminal bronchioles) versus respiratory zone (respiratory bronchioles, alveolar ducts and sacs).
  • Cartilage and mucous glands are absent from bronchioles.
  • Parasympathetic (vagus) causes bronchoconstriction; sympathetic causes bronchodilation.

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. Hall JE, Hall ME. Guyton and Hall Textbook of Medical Physiology. Elsevier, 14th edition (2020) — Tier 3 (textbook)

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