Histology · Respiratory system
The airway: from nose to bronchioles !
- Organ
The tubes that carry air are lined by a moist, ciliated layer that traps dust and germs; their support changes from cartilage to muscle as they narrow.
Updated 2026-11-01
See it in 3D: Nasal cavity · Pharynx · Epiglottis · Vocal folds · Trachea · Main bronchi · Lobar bronchi · Segmental bronchi
What it is
The conducting airway warms, moistens and cleans air before it reaches the alveoli. Its wall changes in a predictable way from the nose to the terminal bronchiole: cartilage and glands fade out, smooth muscle takes over, and the tall ciliated lining becomes lower and simpler. Knowing this sequence lets you name a segment from a description of its slide and explains where asthma, chronic bronchitis and smoking damage act.
Structure
- Nasal vestibule: keratinized stratified squamous epithelium with hairs; the rest of the nasal cavity has respiratory epithelium, and the roof carries the olfactory epithelium.
- Respiratory epithelium: pseudostratified ciliated columnar with goblet cells, resting on a thick basement membrane.
- Larynx: the epiglottis has an elastic cartilage core; the true vocal folds are covered by non-keratinized stratified squamous epithelium to withstand vibration.
- Trachea: C-shaped rings of hyaline cartilage open posteriorly, where the trachealis smooth muscle closes the gap; seromucous glands lie in the submucosa.
- Bronchi: irregular plates of hyaline cartilage, a spiral layer of smooth muscle and submucosal glands.
- Bronchioles: no cartilage and no glands; a thick ring of smooth muscle; epithelium becomes simple columnar to cuboidal, and goblet cells give way to club cells.
Function
- The mucociliary escalator: goblet cells and glands make mucus that traps particles, and cilia beat it toward the pharynx.
- Cartilage keeps the larger airways open during breathing; bronchiolar smooth muscle sets airway resistance.
- Club cells secrete protective proteins, break down inhaled toxins and help renew the bronchiolar epithelium.
The airway segment by segment
| Segment | Epithelium | Cartilage | Glands | Smooth muscle |
|---|---|---|---|---|
| Nasal cavity | Keratinized squamous in the vestibule, then respiratory epithelium; olfactory at the roof | Nasal cartilages and bone in the wall | Abundant seromucous glands | None in the mucosa |
| Larynx and vocal folds | Respiratory, but non-keratinized stratified squamous on the true vocal folds and much of the epiglottis | Hyaline (thyroid, cricoid) and elastic (epiglottis) | Present, absent in the vocal fold itself | Skeletal muscle (intrinsic laryngeal muscles) |
| Trachea | Pseudostratified ciliated columnar with goblet cells | C-shaped hyaline rings | Seromucous, in the submucosa | Trachealis, posterior |
| Bronchi | Pseudostratified ciliated columnar with goblet cells | Irregular hyaline plates | Seromucous, in the submucosa | Spiral layer, more prominent |
| Bronchioles | Simple columnar to cuboidal, ciliated; club cells appear | None | None | Thick ring, relatively the most |
| Respiratory bronchioles | Low cuboidal, interrupted by alveoli | None | None | Scattered bundles |
Clinical notes
- Asthma: goblet cell increase, thickened basement membrane, larger smooth muscle mass and eosinophils in the wall.
- Chronic bronchitis: enlarged submucosal glands (a high Reid index, the gland-to-wall thickness ratio) and excess mucus.
- Smoking: the ciliated lining can turn into stratified squamous epithelium (squamous metaplasia), which no longer clears mucus.
- Primary ciliary dyskinesia (Kartagener syndrome): defective dynein arms cause bronchiectasis, sinusitis and, in some, situs inversus.
Test yourself
Think of the answer, then tap the question to see it.
Which is the first airway segment that has no cartilage and no glands?
The bronchiole. Its wall is held by smooth muscle and the surrounding lung tissue, which is why bronchospasm narrows it so effectively.
Why are the true vocal folds lined by stratified squamous epithelium?
They vibrate and rub against each other with every sound; a layered squamous lining resists that mechanical wear better than a ciliated one.
What closes the posterior gap of the tracheal cartilage rings?
The trachealis smooth muscle and a fibroelastic membrane, which let the esophagus behind it expand during swallowing.
Which cell in terminal bronchioles has secretory and detoxifying roles and replaces goblet cells?
The club cell (formerly Clara cell), a dome-shaped non-ciliated cell.
See it in 3D
The structures of Durgical's 3D anatomy where it is found.
Related
- The alveolus: type I and II pneumocytes, surfactant, the blood–air barrier
- Cilia, microvilli and stereocilia
- Simple, stratified, pseudostratified and transitional epithelium
- Cartilage: hyaline, elastic, fibrocartilage
Related conditions
Microorganisms
Educational content on normal microscopic structure and its clinical relevance; no substitute for studying slides or for a health professional's advice.
Sources: 22.1 Organs and Structures of the Respiratory System - Anatomy and Physiology 2e | OpenStax (OpenStax (Rice University), 2022); Larynx & Trachea | SEER Training (National Cancer Institute (SEER Training), 2026); Bronchi, Bronchial Tree, & Lungs | SEER Training (National Cancer Institute (SEER Training), 2026).
Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake
Representative model, for educational purposes only.