(A part of) endoplasmic reticulum that is tubular in form (rather than sheet-like) and lacks ribosomes, hence, it is called 'smooth'.
Its functions include lipid synthesis, carbohydrate metabolism, calcium concentration, drug detoxification, and attachment of receptors on cell membrane.
Variant: smooth endoplasmic reticulum.
Compare: rough endoplasmic reticulum.
See also: endoplasmic reticulum.