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Exosomes are extracellular vesicles having a unique biogenesis pathway via multivesicular bodies. Exosome formation starts with the invagination of the multi-vesicular bodies (MVBs) or late endosomes to generate intraluminal vesicles (ILVs). [58] There are various proposed mechanisms for formation of MVBs, vesicle budding, and sorting.
Extracellular vesicles (EVs) are lipid bilayer-delimited particles that are naturally released from almost all types of cells but, unlike a cell, cannot replicate. EVs range in diameter from near the size of the smallest physically possible unilamellar liposome (around 20-30 nanometers) to as large as 10 microns or more, although the vast majority of EVs are smaller than 200 nm.
Microvesicles (ectosomes, or microparticles) are a type of extracellular vesicle (EV) that are released from the cell membrane. [1] In multicellular organisms, microvesicles and other EVs are found both in tissues (in the interstitial space between cells) and in many types of body fluids. [ 2 ]
The influx of Ca 2+ ions causes the secretion of insulin stored in vesicles through the cell membrane. The process of insulin secretion is an example of a trigger mechanism in a signal transduction pathway because insulin is secreted after glucose enters the beta cell and that triggers several other processes in a chain reaction.
Increased insulin levels cause the uptake of glucose into the cells. GLUT4 is stored in the cell in transport vesicles, and is quickly incorporated into the plasma membrane of the cell when insulin binds to membrane receptors. [24] Under conditions of low insulin, most GLUT4 is sequestered in intracellular vesicles in muscle and fat cells.
Upon reaching the plasmalemma, the vesicles fuse with the membrane, increasing the number of GLUT4 transporters expressed at the cell surface, and hence increasing glucose uptake. GLUT4 has a Km value for glucose of about 5 mM, which as stated above is the normal blood glucose level in healthy individuals.
Vesicles can also fuse with other organelles within the cell. A vesicle released from the cell is known as an extracellular vesicle. Vesicles perform a variety of functions. Because it is separated from the cytosol, the inside of the vesicle can be made to be different from the cytosolic environment. For this reason, vesicles are a basic tool ...
Uptake of extracellular molecules is also believed to be specifically mediated via receptors in caveolae. From left to right: Phagocytosis, Pinocytosis, Receptor-mediated endocytosis. Potocytosis is a form of receptor-mediated endocytosis that uses caveolae vesicles to bring molecules of various sizes into the cell. Unlike most endocytosis that ...