The endoplasmic reticulum is a membrane-bound cell organelle that is made up of a complex network of tubes and is located in the cytoplasm of the eukaryotic cell. The structure of the endoplasmic reticulum contains three regions namely, cisternae, vesicles, and tubules.
Cisternae are long, flattened, and sac-like structures that are arranged parallelly in bundles inside the endoplasmic reticulum that consists of numerous macromolecules and small granules. The size of cisternae ranges from 40-50 nm in thickness.