Smooth Endoplasmic Reticulum
The Smooth Endoplasmic Reticulum is a structure that is composed of membranes that is responsible for synthesizing steroids within cells and breaking down toxins in the liver. This structure is sometimes abbreviated SER. It is not to be confused with the Rough Endoplasmic Reticulum, abbreviated RER, which has ribosomes on its surface and is mainly responsible for the synthesis of proteins. They both play vital roles in the synthesis and exportation of substances in cells, but serve somewhat different purposes in the kinds of substance that they produce.