The smooth endoplasmic reticulum is the organelle responsible for the production of lipids in the cell. This particular reticulum also synthesizes carbohydrates and steroid hormones.
The endoplasmic reticulum is made up of membranous sacs and tubules. It has two different portions: the smooth endoplasmic reticulum and the rough endoplasmic reticulum. The rough endoplasmic reticulum is studded with ribosomes and produces proteins that are incorporated into cellular membranes outside of the cell.
The smooth endoplasmic reticulum lacks ribosomes on its cytoplasmic surface. It is especially important in muscle cells, where the specialized sarcoplasmic reticulum stores calcium ions, which are needed for triggering contraction of muscle cells.