A signaling network called the UPR reduces stress in this organelle.
A signaling network called the UPR reduces stress in this organelle. The enzyme PDI is located in this organelle, which is the first stage of the secretory pathway. Proteins bearing the KDEL sequence return to this organelle, which can be entered through the translocon. Vesicles coated with COPII mediate transport from this organelle to the Golgi apparatus. Ryanodine receptors are found in a special form of this organelle found in some muscle cells that releases calcium ions. This organelle is the site of lipid synthesis as well as drug detoxification. For 10 points, name this organelle divided into "smooth" and "rough" types, the latter of which is studded with ribosomes. 
A signaling network called the UPR reduces stress in this organelle.
ER [or endoplasmic reticulum; or sarcoplasmic reticulum] 