Endoplasmic Reticulum

Categories: Anatomy; cellular biology

The endoplasmic reticulum is a network of sacs in the cytosol ofeukaryotic cells that manufactures, processes, transports, and stores chemical compounds for use inside and outside of the cell.

The endoplasmic reticulum (ER) is an extensive, complex system of a more or less continuous distribution of convoluted membrane-bound cavities that take up a sizable portion of the cytosol. The internal space of the ER is called the lumen. The ER is attached to the double-layered nuclear envelope and provides a connection, or bridge, between the nucleus and the cytosol. In addition, it provides living bridges between cells by way of the plasmodes-mata, small tubes that connect plant cells. The ER is a dynamic structure, constantly changing. It accounts for 10 percent or more of the volume of the cytosol.

In general, there are two kinds of endoplasmic reticulum, rough and smooth. Smooth ER is quite varied in appearance and most likely in function as well. Through a microscope, it appears as numerous nearly circular blotches, indicating that it consists of interlocking tubes of membranes. On the other hand, rough ER almost always appears as stacks of double membranes that are heavily dotted with ribosomes. Based on the consistent appearance of rough ER, it most likely consists of parallel sheets of membrane, rather than the tubular sheets that characterize smooth ER. These flattened, interconnected sacs are called cisternae, or cisternal cells. The cisternal cells of rough ER are also referred to as luminal cells. Rough ER and the Golgi complex are both composed of cisternal cells.

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