Smooth E.R. is found in many cell types & consists of tubules and vesicles that branch forming a network, which allows increased surface area for the action or storage of key enzymes & the products of these enzymes.
SER packages proteins for transport, synthesizes lipids, membrane phospho-lipids,& fatty acids, carbohydrates, & releases calcium. Other functions, especially in liver cells, includes transformation of bile pigments, glycogenolysis (breakdown of glycogen), & detoxification of drugs (as phenobarbital & barbituates).
muscle cells the SER vesicles & tubules store calcium, which is released during the contraction process. In adrenal cortical cells & in the gonads, SER metabolize the steroid hormone.
striated muscles, the endoplasmic reticulum (called the Sarcoplasmic Reticulum) is involved in the conduction of contracting impulses from the surface membrane of the cell into the depths of the muscle cell filled with muscle filaments, which are the basis for muscle contraction.
Smooth Endoplasmic Reticulum images - U. Illinois