Cilia, microvilli and stereocilia !
- Topic
These are projections of the cell surface: cilia sweep mucus, microvilli absorb, and stereocilia sense sound.
Updated 2026-11-01
See it in 3D: Trachea · Uterine tubes · Jejunum · Epididymis · Cochlea
What it is
The apical surface of many cells carries projections with different jobs. Motile cilia have a microtubule core and beat to move mucus or eggs; microvilli, with an actin core, multiply the absorptive surface; stereocilia are long microvilli that do not move by themselves. Failure of cilia causes primary ciliary dyskinesia.
Structure
- On H&E, cilia look like a fine, even fringe on the pseudostratified columnar epithelium of the airway, with a dark line of basal bodies beneath.
- Intestinal microvilli form a bright pink band, the striated border, which is PAS positive because of its glycocalyx.
- Epididymal stereocilia look like long, clumped tufts reaching into the duct lumen.
Apical projections
| Projection | Core | Moves? | Where | Clinical |
|---|---|---|---|---|
| Motile cilium | 9+2 microtubule axoneme with dynein arms; basal body of 9 triplets | Yes, coordinated beating | Trachea and bronchi, uterine tube, ependyma | Primary ciliary dyskinesia; Kartagener syndrome |
| Primary cilium | 9+0 axoneme | No; sensory | Almost all cells, for example renal tubules | Polycystic kidney disease |
| Flagellum | 9+2 axoneme | Yes | Sperm | Male infertility from immotile sperm |
| Microvilli | Actin bundle | No | Small intestine (striated border), proximal tubule (brush border) | Coeliac disease: villous atrophy and loss of brush-border enzymes |
| Stereocilia | Long actin bundle | No | Epididymis and ductus deferens; inner-ear hair cells | Sensorineural hearing loss from hair-cell damage |
Clinical notes
- Primary ciliary dyskinesia: almost always autosomal recessive; recurrent sinusitis, otitis and bronchiectasis, male infertility and a higher risk of ectopic pregnancy.
- Kartagener syndrome: primary ciliary dyskinesia with situs inversus (about 4 in 10 patients have mirror-image organs).
- Diagnosis combines low nasal nitric oxide, electron microscopy of the axoneme and genetic testing.
Test yourself
Think of the answer, then tap the question to see it.
Which ultrastructural defect is typical of primary ciliary dyskinesia?
Missing or defective dynein arms in the 9+2 axoneme, which stops the cilia beating.
What is the triad of Kartagener syndrome?
Situs inversus, chronic sinusitis and bronchiectasis; infertility usually comes with it.
Which protein forms the core of microvilli?
Actin, arranged as a bundle of microfilaments.
In which organ do stereocilia absorb fluid?
In the epididymis (and the ductus deferens).
See it in 3D
The structures of Durgical's 3D anatomy where it is found.
Related
- Cytoskeleton: microfilaments, intermediate filaments, microtubules
- The airway: from nose to bronchioles
- Small intestine: villi, crypts, enterocytes, Paneth cells; duodenum vs jejunum vs ileum
- Uterine tube
- Epididymis, vas deferens, seminal glands and prostate
- Inner ear: the cochlea and the organ of Corti
- Electron microscopy: what it shows that light can't
Related conditions
Educational content on normal microscopic structure and its clinical relevance; no substitute for studying slides or for a health professional's advice.
Sources: 4.2 Epithelial Tissue (OpenStax (Rice University), 2022); Primary ciliary dyskinesia (MedlinePlus Genetics (U.S. National Library of Medicine), 2024).
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Representative model, for educational purposes only.