The smooth endoplasmic reticulum (smooth ER) is a type of endoplasmic reticulum and is continuous with the rough ER but has few or no ribosomes on its cytoplasmic surface. Functions of the smooth ER include:
- Synthesis of carbohydrates, lipids, and steroid hormones.
- Detoxification of medications and poisons
- Storage of calcium ions
In muscle cells, a special type of smooth ER called the sarcoplasmic reticulum is responsible for storage of calcium ions which are needed to trigger the coordinated contractions of muscle fibers.
There are also tiny “smooth” patches of ER found within the rough ER. These patches serve as exit sites for vesicles budding off from the rough ER and are called transitional ER.