The endoplasmic reticulum is a delicate membranous structure contiguous
to the nuclear membrane and present in the cytoplasm. It forms an
extensive net of channels throughout the cell and is classified into
rough or smooth types.
The rough endoplasmic reticulum has a great number of ribosomes attached
to the external side of its membrane. The smooth endoplasmic reticulum
does not have ribosomes attached to its membrane.
The main functions of the rough endoplasmic reticulum are synthesis and
storage of proteins made in the ribosomes. The smooth endoplasmic
reticulum plays a role in the lipid synthesis and, in muscle cells, it
is important in the conduction of the contraction stimulus.
