Pseudostratified columnar epithelium
Epithelium pseudostratificatum columnare
Also known as: respiratory epithelium, pseudostratified ciliated columnar epithelium
A single layer of cells of different heights, all resting on the basement membrane but not all reaching the surface, so their nuclei lie at different levels and the tissue looks stratified; typically ciliated with goblet cells ("respiratory epithelium").
Overview
The key to recognising it is that every cell contacts the basement membrane (making it a simple epithelium), but short basal cells do not reach the lumen while tall columnar cells do; the nuclei are therefore scattered at several levels, giving a false impression of layering.
Ciliated pseudostratified columnar epithelium with goblet cells lines most of the conducting airway — nasal cavity, paranasal sinuses, nasopharynx, larynx (except the vocal folds and epiglottis), trachea and bronchi — as well as the auditory tube. It contains ciliated cells (most numerous), mucus-secreting goblet cells, basal cells (stem cells that regenerate the epithelium), brush cells (chemosensory) and scattered neuroendocrine (Kulchitsky) cells. Mucus traps inhaled particles and microbes, and coordinated ciliary beating moves the mucus blanket toward the pharynx — the mucociliary escalator.
A non-ciliated variety, bearing long stereocilia (absorptive microvilli), lines the epididymis and ductus deferens; pseudostratified epithelium also occurs in parts of the male urethra.
- Location
Nasal cavity, paranasal sinuses, nasopharynx, larynx, trachea, bronchi, auditory tube (ciliated); epididymis, ductus deferens (stereocilia).
Anatomy
- Histology
Nuclei at multiple levels; tall ciliated cells with a line of basal bodies; pale goblet cells; prominent basement membrane in the trachea, thickened in asthma.
Function
- Mucociliary clearance of the airways.
- Warming and humidifying inspired air (with the underlying vascular lamina propria).
- Absorption of testicular fluid (epididymis).
Clinical significance
Squamous metaplasia in smokers
Chronic irritation replaces ciliated epithelium with more resistant stratified squamous epithelium, losing mucociliary clearance; dysplasia here may lead to squamous cell carcinoma of the lung.
Chronic bronchitis and cystic fibrosis
Goblet-cell hyperplasia and submucosal gland hypertrophy (Reid index > 0.5; normal < 0.4) produce excess mucus in chronic bronchitis; in cystic fibrosis dehydrated, viscous mucus cannot be cleared, leading to infection and bronchiectasis.
Test yourself
The trachea is lined by:
- Simple columnar epithelium with microvilli
- Stratified squamous non-keratinised epithelium
- Pseudostratified ciliated columnar epithelium with goblet cells
- Simple cuboidal epithelium
Answer: Pseudostratified ciliated columnar epithelium with goblet cells
"Respiratory epithelium": all cells touch the basement membrane but not all reach the lumen, so nuclei lie at different levels. Cilia and goblet-cell mucus form the mucociliary escalator.
Compiled from standard anatomy and physiology references — see the Cells & Tissues sources. For education only; not medical advice.