Bronchioles are the small airways, usually under about 1 mm across, that branch from the bronchi deep within the lungs. Unlike bronchi, they have no cartilage and no mucous glands, so their size depends on the surrounding lung tissue and their smooth muscle. The last purely air-conducting branches are the terminal bronchioles.
| Location | Throughout each lung, within the pulmonary lobules, between the smallest bronchi and the respiratory bronchioles. |
|---|---|
| Parts |
|
| Nerve Supply | Pulmonary plexus; Vagus nerve (parasympathetic, bronchoconstriction and mucus secretion); Sympathetic fibres from T2-T5 ganglia (bronchodilation) |
| Blood Supply | Bronchial arteries |
| Lymphatic drainage |
|
Conduct air to the gas exchange regions and control airflow resistance by contraction and relaxation of their smooth muscle. Club cells secrete protective proteins and help repair the lining.
Because they lack cartilage, bronchioles narrow easily with smooth muscle spasm, swelling and mucus, which is why asthma and COPD affect them so strongly. Inhaled bronchodilators relax their muscle and are often used before exercise in people with exercise-induced bronchoconstriction. Damage to small airways can be present long before standard lung function tests become abnormal.
Chronic airway inflammation with reversible narrowing, largely of the bronchi and bronchioles. Triggers include allergens, cold air and exercise.
Viral infection of the bronchioles, most often from RSV in infants. It causes wheeze, cough and difficulty feeding and breathing.
Scarring and blockage of the bronchioles after toxic inhalation, infection or lung transplantation. It causes progressive, fixed airflow obstruction.
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