Rough Endoplasmic Reticulum (RER)

Rough endoplasmic reticulum (rer) is organised as a series of interconnected and flattened membrane-bound compartments called cisternae. The outer sides of the membranes have a rough appearance due to the presence of ribosomes (see arrow on image below). This organelle plays a very important role in protein formation and therefore is very abundant in cells that are active in protein production e.g. liver and pancreas.

The image below is a transmission electron microscope picture of a section through some rer.