alpha granules

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α gran·ules

large, rodlike, or filamentous granules found in several types of cells, especially platelets, where they are the most numerous type of granule; contain secretory proteins, including fibrinogen, fibronectin, fibrospondin, von Willebrand factor (collectively known as adhesive proteins) and other proteins (for example, platelet factor 4, platelet-derived growth factor, coagulation factor V).