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PH-RS14

Laryngitis, bronchitis and bronchiolitis

How inflammation narrows the airway at each level: swollen vocal folds in laryngitis, the subglottis in croup and the supraglottis in epiglottitis, the bronchi in acute and chronic bronchitis, and infants’ bronchioles in RSV bronchiolitis.

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  • 5 steps · 10 questions
  • 3D anatomy, affected parts marked

By the end, you can

  • Describe the supraglottis, glottis and subglottis, the bronchial lining and the bronchioles, and explain why small airways are so easily blocked.
  • Compare acute laryngitis, croup and epiglottitis by cause, site of swelling and findings, and explain why croup causes inspiratory stridor.
  • Explain why acute bronchitis causes a cough that outlasts the infection, and how chronic bronchitis differs in cause, structure and definition.
  • Explain how RSV bronchiolitis leads to air trapping, collapse and low oxygen in infants, and how obliterative bronchiolitis causes fixed obstruction.
  • Recognise the classic signs, scores and tests of these conditions, and explain how glucocorticoids, adrenaline, antibiotics, oxygen and RSV antibodies act.

What it is

Inflammation of the airway named by its level: laryngitis (the larynx, including croup, a viral laryngotracheobronchitis of young children, and epiglottitis, a bacterial infection of the supraglottis), bronchitis (the trachea and bronchi; acute and infective, or chronic and defined by daily sputum) and bronchiolitis (the small airways; acute and viral in infants, or scarring in obliterative bronchiolitis).

4 types to tell apart
Acute and chronic laryngitis
Swollen vocal folds from a viral infection, voice overuse or irritants; chronic after more than about three weeks, mainly from smoking and reflux.
Croup and epiglottitis
Croup: viral swelling of the subglottis in young children. Epiglottitis: bacterial cellulitis of the supraglottis, now mostly in adults.
Acute and chronic bronchitis
Acute: viral inflammation of the trachea and bronchi with a cough for weeks. Chronic: daily sputum for months, from smoking; part of COPD.
Acute and obliterative bronchiolitis
Acute: viral, mostly RSV, in infants, and reversible. Obliterative: scar tissue narrows bronchioles for good, as in lung transplant rejection.

Normal function

The larynx and the airway below it

Air passes the larynx on its way to the lungs. Above, the and the aryepiglottic folds form the supraglottis, whose mucosa is loosely attached and swells easily. The form the glottis; the gap between them, the , is the narrowest part of the adult airway. Below lies the subglottis, ringed by the , the only complete ring of cartilage in the airway, so swelling there can only narrow the lumen inwards.

The vocal folds are covered by stratified squamous epithelium over a loose layer (Reinke’s space) that lets their surface ripple as air passes; anything that thickens the folds changes their vibration and the voice. Below the glottis, the and bronchi have cartilage in their walls and a ciliated lining with goblet cells and submucosal glands: the mucociliary escalator, which carries mucus up to be swallowed or coughed out. The bronchioles, under about 1 mm across, have no cartilage or glands and are held open by the elastic pull of the lung around them.

Small airways are easily blocked. Resistance to flow rises steeply as an airway narrows, with the fourth power of the radius in the usual teaching model (Poiseuille’s law): in an infant airway about 4 mm across, 1 mm of swelling all round halves the radius and raises resistance about sixteen-fold. Infants also have narrow bronchioles, few side channels between neighbouring alveoli and a soft chest wall that is sucked in when they work hard to breathe.

Point to it on the model