Cilium (redirected from Cirrus (organ))

cilium

Short, eyelashlike filament that is numerous on tissue cells of most animals. Capable of beating in unison, cilia perform a variety of functions, including providing the means of locomotion for some protozoans, moving mammalian ova (eggs) through oviducts, generating water currents to carry food and oxygen past the gills of clams, and cleaning debris from mammalian respiratory systems. Like a flagellum, a cilium has a central core consisting of two central microtubules surrounded by an outer ring of nine double fibres. Ciliary outgrowth is controlled by the basal body, located just inside the cell surface at the base of the cilium. Beneath the surface of some cells is a network of microtubular bundles that may coordinate ciliary beating.

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cilium

1. any of the short thread-like projections on the surface of a cell, organism, etc., whose rhythmic beating causes movement of the organism or of the surrounding fluid

2. the technical name for eyelash

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Cilium 

a slender filamentous or setaceous process found on cells that is capable of rhythmic movements. Among Protozoa, cilia are characteristic of infusorians. In some lower multicellular animals, such as turbellarians, cilia are found on all external covering elements (integumentary epithelium). The larvae of most coelenterates and sponges have a ciliated covering. In vertebrates, including humans, only a few specialized cells have cilia. For example, in man cilia cover the epithelium of the respiratory tract, the eustachian tubes, the vasa deferentia, the oviducts, and the uterus. Locomotor activity of the cilia ensures movement of the cell in a fluid medium; a ciliated cell that is fixed to a substrate produces currents of fluid in the surrounding medium.

The average cilium has a length of 5–15 microns and a diameter of 0.1–0.6 microns. The number of cilia on one cell ranges from ten to 22 in man to 2,500–15,000 in infusorians. The ultra-structures of cilia and flagella are identical. Externally cilia are covered with a three-layered membrane that becomes the surface membrane of the cell. In the center are two central tubular fibrils, which extend the length of the cilia, and nine peripheral fibrils, each of which is double. In the superficial layers of the cell cytoplasm, each cilium originates from the basal body, which has a structure similar to that of the cilium but lacks the central fibrils. The peripheral fibrils cause movement of the cilium, and the central ones apparently play a supportive role and possibly serve to conduct excitation.

IU. I. POLIANSKII