host intracellular membrane-bounded organelle host cell cytoplasm part host cell endoplasmic reticulum cellular_component host endoplasmic reticulum 2009-09-04T11:08:09Z GO:0044165 jl The irregular network of unit membranes, visible only by electron microscopy, that occurs in the host cell cytoplasm of many eukaryotic cells. The membranes form a complex meshwork of tubular channels, which are often expanded into slitlike cavities called cisternae. The host ER takes two forms, rough (or granular), with ribosomes adhering to the outer surface, and smooth (with no ribosomes attached).