Smooth endoplasmic reticulum

 The smooth endoplasmic reticulum is the part of the endoplasmic reticulum (ER) which does not have ribosomes bound to it, thus not exhibiting the bumpy appearance shown by the rough endoplasmic reticulum. It is from these smooth areas of the ER that vesicles bud off, transporting lipids and proteins synthesised by the ribosomes of the rough endoplasmic reticulum, to the Golgi apparatus and other parts of the cell. The majority of cells do not have much smooth Er, however there are a few examples of specialised cells with large amounts of smooth Er. In particular the hepatocyte cells of the liver, which produce lipid carrying lipoprotein particles, which must be transported around the body. The sarcoplasmic reticulum of muscles is also a modified form of the smooth endoplasmic reticulum (Alberts et al., 2008).

References

Alberts, Johnson, Lewis, Raff, Roberts, Walter (2008) molecular Biology of The Cell, 5th Edition, Garland Science. Pages 724-725.