an extensive intracellular membrane system whose functions include synthesis and transport of lipids and, in regions where ribosomes are attached, of proteins
endoplasmic reticulum in American English
a system of folded membranes, channels, and flattened sacs in the cytoplasm of eukaryotic cells, involved in the synthesis, storage, and transport of various substances necessary to cell function: as the point of attachment for ribosomes, it is especially associated with protein synthesis