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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.
Microtubule and tubulin metrics [1]. Microtubules are polymers of tubulin that form part of the cytoskeleton and provide structure and shape to eukaryotic cells. Microtubules can be as long as 50 micrometres, as wide as 23 to 27 nm [2] and have an inner diameter between 11 and 15 nm. [3]
Radial microtubules: They are located in the proximal regions of the ramified processes of oligodendrocytes, that extend outward from the cell body. Lamellar microtubules : They are the microtubules that eventually wrap around the axon, forming the myelin sheath .
Microvilli on the apical surface increase its surface area. This facilitates transport of numerous small molecules into the enterocyte from the intestinal lumen . These include broken down proteins , fats , and sugars , as well as water, electrolytes , vitamins , and bile salts .
Stereocilia are cylindrical and non-motile. They are much longer and thicker than microvilli, form single "finger-like" projections that may be branched, and have more of the characteristics of the cellular membrane proper. Like microvilli, they contain actin [1] and lack an axoneme. This distinguishes them from cilia.
Stereocilia of the epididymis are not cilia because their cytoskeleton is composed of actin filaments, not microtubules. [3] They are structurally and molecularly more similar to microvilli than to true cilia. [dubious – discuss] Pseudostratified columnar epithelia are found forming the straight, tubular glands of the endometrium in females. [4]
Filled with cytoplasm, pseudopodia primarily consist of actin filaments and may also contain microtubules and intermediate filaments. [1] [2] Pseudopods are used for motility and ingestion. They are often found in amoebas. Different types of pseudopodia can be classified by their distinct appearances. [3] Lamellipodia are broad and thin.
The microvilli and pseudopodia play a role in the endocytosis of particles. The nucleus is indented and ovoid, and can be lobulated. Notable cytoplasmic elements include ribosomes , Golgi complexes , centrioles , microtubules and microfilaments .