Intracellular membrane-coating granules

When the role of the endoplasmic reticulum is taken into account, the importance of its tridimensional structure becomes obvious. To fulfill the first three of these physiological roles, a system of individual tubules or vesicles, coated or not with widely interconnected granules may be sufficient. But if the endoplasmic reticulum is also to function as an intracellular circulatory system, it should probably constitute a tridimensional network of canaliculi extending throughout the entire volume of the cytoplasm from the cell membrane to the nuclear membrane. 

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