[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Histology](https://durgical.com/en/histology/) › [The cell](https://durgical.com/en/histology/#a-cell) › Cilia, microvilli and stereocilia [Histology](https://durgical.com/en/histology/) · [The cell](https://durgical.com/en/histology/#a-cell) # 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](https://durgical.com/en/anatomy/trachea/) · [Uterine tubes](https://durgical.com/en/anatomy/uterine-tube/) · [Jejunum](https://durgical.com/en/anatomy/jejunum/) · [Epididymis](https://durgical.com/en/anatomy/epididymis/) · [Cochlea](https://durgical.com/en/anatomy/cochlea/) ## Key points - Motile cilium = 9+2 microtubules + dynein; microvillus and stereocilium = actin. - Kartagener: situs inversus + chronic sinusitis + bronchiectasis (+ infertility). - Nodal cilia in the embryo set left-right asymmetry, which is why laterality fails in dyskinesia. - Primary cilium 9+0, sensory: its dysfunction is part of polycystic kidney disease. - Stereocilia: epididymis (absorption) and inner ear (mechanotransduction). ## 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](https://durgical.com/en/conditions/bronchiectasis/) | 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](https://durgical.com/en/conditions/autosomal-dominant-polycystic-kidney-disease/) | 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](https://durgical.com/en/conditions/coeliac-disease/) | 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. ## Memory aid Cilia sweep, microvilli sip, stereocilia listen: three projections, three jobs. ## 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). [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/histology/cilia-microvilli-and-stereocilia/) ## See it in 3D The structures of Durgical's 3D anatomy where it is found. - [Trachea](https://durgical.com/en/anatomy/trachea/) - [Uterine tubes](https://durgical.com/en/anatomy/uterine-tube/) - [Jejunum](https://durgical.com/en/anatomy/jejunum/) - [Epididymis](https://durgical.com/en/anatomy/epididymis/) - [Cochlea](https://durgical.com/en/anatomy/cochlea/) ## Related - [Cytoskeleton: microfilaments, intermediate filaments, microtubules](https://durgical.com/en/histology/cytoskeleton-microfilaments-intermediate-filaments-microtubules/) - [The airway: from nose to bronchioles](https://durgical.com/en/histology/the-airway-from-nose-to-bronchioles/) - [Small intestine: villi, crypts, enterocytes, Paneth cells; duodenum vs jejunum vs ileum](https://durgical.com/en/histology/small-intestine-villi-crypts-enterocytes-paneth-cells-duodenum-vs-jejunum-vs-ile/) - [Uterine tube](https://durgical.com/en/histology/uterine-tube/) - [Epididymis, vas deferens, seminal glands and prostate](https://durgical.com/en/histology/epididymis-vas-deferens-seminal-glands-and-prostate/) - [Inner ear: the cochlea and the organ of Corti](https://durgical.com/en/histology/inner-ear-the-cochlea-and-the-organ-of-corti/) - [Electron microscopy: what it shows that light can't](https://durgical.com/en/histology/electron-microscopy-what-it-shows-that-light-can-t/) ## Related conditions - [Bronchiectasis](https://durgical.com/en/conditions/bronchiectasis/) - [Autosomal dominant polycystic kidney disease](https://durgical.com/en/conditions/autosomal-dominant-polycystic-kidney-disease/) - [Coeliac disease](https://durgical.com/en/conditions/coeliac-disease/) [← All of histology](https://durgical.com/en/histology/) 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](https://openstax.org/books/anatomy-and-physiology-2e/pages/4-2-epithelial-tissue) (OpenStax (Rice University), 2022); [Primary ciliary dyskinesia](https://medlineplus.gov/genetics/condition/primary-ciliary-dyskinesia/) (MedlinePlus Genetics (U.S. National Library of Medicine), 2024). ## **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. --- Source: https://durgical.com/en/histology/cilia-microvilli-and-stereocilia/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/histology/cilia-microvilli-and-stereocilia/