The endoplasmic reticulum (ER) is an extensive network of membrane tubules, vesicles and flattened cisternae (sac-like structures) found throughout the eukaryotic cell, especially those responsible for the production of hormones and other secretory products. The membrane is a continuation of the outer nuclear membrane, it encloses the cytosol cisternal spaces (or internal lumen), which are continuous with the nuclear periplasmic space. The ER sustains many general functions, including protein synthesis, protein modification, protein folding, insertion of membrane proteins, sequestration of calcium, production of phospholipids and steroids and transport of proteins destined for membranes and secretion.

› Cellular component

› Endoplasmic reticulum

› endoplasmic reticulum [ GO:0005783 ]