Endoplasmic reticulum is composed of two different regions that each have a distinct shape. Rough endoplasmic reticulum is composed of a series of flattened sacs with attached ribosomes on the membrane. Smooth endoplasmic reticulum consists of a tube-shaped network and does not have attached ribosomes.
Rough endoplasmic reticulum produces membranes and proteins that are transferred to various destinations. In certain types of cells, the rough endoplasmic reticulum produces antibodies and insulin. Smooth endoplasmic reticulum is involved in carbohydrate synthesis, lipid synthesis, enzyme production, hormone synthesis and the contraction of muscle cells. It serves as a staging area for the transport of endoplasmic reticulum products, including those manufactured in the rough endoplasmic reticulum.
Endoplasmic reticulum is one of several structures found in a typical animal eukaryotic cell. It was first observed with an electron microscope in 1945.