Ciliated

Ciliated refers to cells or organisms that bear cilia, hairlike projections from the cell surface. Cilia can be motile, generating movement of the cell or a surrounding fluid, or non-motile, serving sensory roles. The term is used for both single-celled organisms with numerous cilia and for multicellular tissues that rely on ciliary action.

Cilia share a common core structure called the axoneme. In most motile cilia, the axoneme has a characteristic nine outer microtubule doublets arranged around two central microtubules (the 9+2 arrangement) and is powered by dynein motor proteins that cause microtubule sliding and bending. This results in a coordinated, whip-like beat. Non-motile or primary cilia typically have a 9+0 axoneme and function mainly as sensory antennas, participating in signaling pathways such as Hedgehog and in mechanosensation. Cilia are anchored to the cell by a basal body derived from a centriole.

Functions of cilia include moving mucus and debris across epithelial surfaces (as in the respiratory tract and the oviduct), propelling single-celled organisms, and detecting mechanical or chemical cues in the environment. Ependymal cells lining the brain ventricles and certain kidney tubule cells also rely on cilia for fluid movement and signaling.

Dysfunction of cilia can cause ciliopathies, a spectrum of disorders. Primary ciliary dyskinesia (Kartagener syndrome) involves impaired motility, recurrent respiratory infections, and sometimes situs inversus. Other ciliopathies include polycystic kidney disease, retinal degeneration, Bardet-Biedl syndrome, and Joubert syndrome. The study of cilia links cellular structure to development, physiology, and disease.