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Membrane protrusions or cell appendages, extend from the cell membrane, and include microvilli, cilia, and flagella. [9] Microvilli increase the surface area of a tissue , such as from their abundance on tissue protrusions such as intestinal villi .
Mammals also have motile cilia or secondary cilia that are usually present on a cell's surface in large numbers (multiciliate), and beat in coordinated metachronal waves. [40] Multiciliated cells are found lining the respiratory tract where they function in mucociliary clearance sweeping mucus containing debris away from the lungs . [ 13 ]
Microvilli (sg.: microvillus) are microscopic cellular membrane protrusions that increase the surface area for diffusion and minimize any increase in volume, [1] and are involved in a wide variety of functions, including absorption, secretion, cellular adhesion, and mechanotransduction.
The microtubule-organizing center (MTOC) is a structure found in eukaryotic cells from which microtubules emerge. MTOCs have two main functions: the organization of eukaryotic flagella and cilia and the organization of the mitotic and meiotic spindle apparatus, which separate the chromosomes during cell division.
Cilia Structure. Primary cilia are found to be formed when a cell exits the cell cycle. [2] Cilia consist of four main compartments: the basal body at the base, the transition zone, the axenome which is an arrangement of nine doublet microtubules and considered to be the core of the cilium, and the ciliary membrane. [2]
The nature of these "hairs" differs, with two basic forms underlying photoreceptor structure: microvilli and cilia. [26] In the eyes of protostomes, they are microvilli: extensions or protrusions of the cellular membrane. But in the eyes of deuterostomes, they are derived from cilia, which are separate structures. [24]
Their apical surfaces are covered in a layer of cilia, which circulate CSF around the CNS. [4] Their apical surfaces are also covered with microvilli , which absorb CSF. Within the ventricles of the brain, a population of modified ependymal cells and capillaries together known as the tela choroidea form a structure called the choroid plexus ...
Cilia and flagella always extend directly from a MTOC, in this case termed the basal body. The action of the dynein motor proteins on the various microtubule strands that run along a cilium or flagellum allows the organelle to bend and generate force for swimming, moving extracellular material, and other roles.