Learning Objective:
Understand the structure, anatomical position, neurovascular supply, and clinical relevance of the trachea, bronchi, and bronchioles.
The Tracheobronchial Tree
The trachea, bronchi, and bronchioles form the tracheobronchial tree – a system of airways that allow passage of air into the lungs, where gas exchange occurs. These airways are located in the neck and thorax.
This article outlines their anatomical position, structure, neurovascular supply, and clinical relevance.
The Trachea
Anatomical Position
The trachea arises at the lower border of the cricoid cartilage. It descends into the superior mediastinum, bifurcating at the level of the sternal angle to form the right and left main bronchi. It lies anterior to the oesophagus and inclines slightly to the right.
Structure
The trachea is supported by C-shaped cartilage rings, with free ends bridged by the trachealis muscle. It is lined by ciliated pseudostratified columnar epithelium with goblet cells forming the mucociliary escalator, which traps and removes particles.
The carina, at the bifurcation of the trachea, is the most sensitive area for triggering the cough reflex.
Neurovascular Supply
Sensory innervation: recurrent laryngeal nerve
Arterial supply: tracheal branches of the inferior thyroid artery
Venous drainage: brachiocephalic, azygos, and accessory hemiazygos veins
Activity
Bronchi
Structure
At the sternal angle, the trachea bifurcates into the right and left main bronchi, which branch into secondary (lobar) bronchi and tertiary (segmental) bronchi. A segmental bronchus supplies each bronchopulmonary segment – the functional unit of the lungs.
The right main bronchus is wider, shorter, and more vertical than the left, predisposing to foreign body inhalation.
Neurovascular Supply
Innervation: pulmonary branches of the vagus nerve (CN X)
Arterial supply: bronchial arteries
Venous drainage: bronchial veins
Activity
Bronchioles
Structure
The smallest airways, bronchioles, lack cartilage and goblet cells. Club cells produce surfactant to prevent airway collapse.
Conducting bronchioles transport air; terminal bronchioles branch into respiratory bronchioles with alveoli – the site of gas exchange. Adults have ~300 million alveoli.
Clinical Correlations: Asthma
Asthma is a chronic inflammatory disorder causing airway hypersensitivity, reversible obstruction, and bronchospasm.
- Small airway remodelling includes thickened smooth muscle, damaged epithelium, and thickened basement membrane.
- Acute “asthma attacks” are triggered by allergens, exercise, or irritants, causing bronchospasm and difficulty breathing with wheezing.
You must be logged in to post a comment.