Bronchus

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Bronchus

Conducting passages.

Front view of cartilages of larynx, trachea, and bronchi.
Gray's	subject #237 1084
MeSH	Bronchi
Dorlands/Elsevier	b_23/12198294

A bronchus (plural bronchi, adjective bronchial) is a caliber of airway in the respiratory tract that conducts air into the lungs. No gas exchange takes place in this part of the lungs.

1 Anatomy
2 Role in disease
3 Additional images
4 References

[edit] Anatomy

The trachea (windpipe) divides into two main bronchi (also mainstem bronchi), the left and the right, at the level of the sternal angle. The right main bronchus is wider, shorter, and more vertical than the left main bronchus. The main bronchi subdivide into two and three secondary bronchi that each serve the left and right lungs, respectively. The lobar bronchi divide into tertiary bronchi. Each of the segmental bronchi supplies a bronchopulmonary segment. A bronchopulmonary segment is a division of a lung that is separated from the rest of the lung by a connective tissue septum. This property allows a bronchopulmonary segment to be surgically removed without affecting other segments. The segmental bronchi divide into many primary bronchioles which divide into terminal bronchioles, each of which then gives rise to several respiratory bronchioles, which go on to divide into 2 to 11 alveolar ducts. There are 5 or 6 alveolar sacs associated with each alveolar duct. The alveolus is the basic anatomical unit of gas exchange in the lung.

There is hyaline cartilage present in the bronchi, present as irregular rings in the larger bronchi (and not as regular as in the trachea), and as small plates and islands in the smaller bronchi. Smooth muscle is present continuously around the bronchi.

[edit] Role in disease

Bronchitis is viral or bacterial infection of the bronchi. Asthma is hyperreactivity of the bronchi with an inflammatory component, often in response to allergens. Chronic bronchitis (COPD) is smoking- or coal dust-induced chronic inflammation of the bronchi that leads to obstruction of the airways.

While the left mainstem bronchus departs from the trachea at an angle, the right mainstem bronchus is almost a vertical continuation of the trachea. This anatomy predisposes the right lung to several problems:

If the endotracheal tube used for intubation is inserted too far, it usually lodges in the right mainstem bronchus. This allows ventilation of the right lung, but leaves the left lung useless.
Aspiration pneumonia preferentially affects the right middle lobe of the lung, since food and liquids take the path of least resistance.
Patients with inadequate cough reflexes may develop chronic right middle lobe lung infections such as the Lady Windermere Syndrome.