Scale bar represents 10µm
The endoplasmic reticulum (ER) is contiguous to the outer of the two nuclear membranes and forms a membranous network throughout the whole cell. It is divided into two parts: the smooth (sER) and the rough endoplasmic reticulum (rER). The rER has ribosomes attached to its cytoplasmic surface and is responsible for the synthesis of transmembrane proteins and proteins that are secreted to the extracellular space. The sER is involved in lipid and steroid synthesis. In addition, the ER is one of major storage sites for intracellular ions maintaining a homeostasis in the cell by a regulated release and uptake of ions.
As the ER is contiguous with the nuclear membrane, it is recognizable by a staining of the nuclear membrane and a network-like staining of the cytosol. It is usually stronger close to the nucleus and weakens as it gets closer to the edges of the cell. The network consists of thin strands that intersect at regular intervals.
Read more about the proteome of the endoplasmic reticulum.