These are a network of tiny tubular structures scattered in the cytoplasm.
ER divides the intracellular space into 2 compartments:luminal (inside ER) & extra luminal (cytoplasm).
Endoplasmic reticulum is 2 types: a. Rough endoplasmic reticulum (RER): Bear ribosomes on their surface. RER is frequently observed in the cells actively involved in protein synthesis and secretion. They are extensive and continuous with the outer membrane of the nucleus b. Smooth endoplasmic reticulum (SER):Ribosomes are absent. SER is the major site for synthesis of lipid. In animal cells lipid-like steroidalhormones are synthesized in SER.
