- A hollow, cylindrical cytoplasmic element, 20–27 nm in diameter and of variable length, that occurs widely in the cytoskeleton, cilia, and flagella of cells; microtubules play a role in the maintenance of cell shape and increase in number during mitosis and meiosis, where they are related to movement of the chromosomes by the nuclear spindle.- subpellicular m. a m. lying beneath the unit membrane (pellicle) of many protozoans, often as a palisade of longitudinally arranged fibrils connected by fine lateral bridges that support the external cell form; in certain sporozoan stages a fixed number of microtubules are found, extending longitudinally from the polar ring. SYN: subpellicular fibril.
* * *mi·cro·tu·bule .mī-krō-'t(y)ü-(.)byü(ə)l n any of the minute tubules in eukaryotic cytoplasm that are composed of the protein tubulin and form an important component of the cytoskeleton, mitotic spindle, cilia, and flagellami·cro·tu·bu·lar -byə-lər adj
* * *mi·cro·tu·bule (mi″kro-tooґbūl) a tubular cytoplasmic structure, 25 nm in diameter and of variable length, composed of α- and β-tubulin dimers, whose orientation imparts polarity; microtubules are involved in maintenance of cell shape and in the movements of organelles and inclusions and form the spindle fibers of mitosis. In cilia and flagella, they are constantly arranged with two single microtubules in the center and nine pairs of doublets arrayed around the central two.
Microtubules in a 9 + 2 array in a cross-section of the axoneme of a cilium.
Medical dictionary. 2011.