Glucagon is processed through a series of steps beginning with its synthesis as a precursor molecule in the endoplasmic reticulum, followed by packaging in the Golgi apparatus, and culminating in final processing within secretory granules before release.
Here's a more detailed breakdown:
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Synthesis: Glucagon, like other polypeptide hormones, begins its life as part of a larger precursor molecule (preproglucagon). This synthesis occurs in the endoplasmic reticulum of alpha cells in the pancreatic islets.
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Packaging: The preproglucagon then moves to the Golgi apparatus, where it's further processed and packaged into vesicles.
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Final Processing and Storage: The final processing of glucagon occurs within specialized structures called secretory granules. Here, enzymes cleave the precursor molecule to yield the active glucagon hormone. These granules store the glucagon until a signal triggers its release.
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Release (Exocytosis): When blood glucose levels drop, the alpha cells are stimulated to release glucagon. This occurs through exocytosis, where the secretory granules fuse with the cell membrane, releasing the glucagon into the bloodstream.
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Metabolism: After circulating and exerting its effects, glucagon is primarily metabolized (broken down) by the liver and kidneys, effectively removing it from circulation.
In summary, glucagon processing involves synthesis, packaging, final modification in secretory granules, and release through exocytosis. The hormone's activity is then terminated by metabolic breakdown primarily in the liver and kidneys.
