There are three types of structure of endoplasmic reticulum. These are-
1. Lamellar or Cisternae: Endoplasmic reticulum that is long, cylindrical, unbranched and compressed is called cisternae. Their diameter is 40-50 millimicrons. Cisternae contain a glycoprotein called ribophorin. The cisternae are connected to each other with the help of ribophorin.
2. Vasicle: The endoplasmic reticulum that looks round or oval or blistered and surrounded by a membrane is called a vesicle. The vesicles are called microsomes. Their diameter is 25-50 mm. Vesicles are abundant in protein-synthesizing pancreatic cells.
3. Tubules: The endoplasmic reticulum which is long, cylindrical and branched is called tubules. Their diameter is 50-190 millimicrons. It stays connected. They have no ribosomes.