Smooth endoplasmic reticulum (sER) consists of an irregular network of membranous tubes and vesicles lacking ribosomes that is continuous with the rER.

Regions of sER in different cells have diverse functions, but one of the most important roles is lipid synthesis.

• For this reason sER is abundant in steroid-secreting cells of endocrine tissues.
• Having no associated RNA and less associated protein than rER, sER stains very poorly with routine LM stains and the cytoplasm of cells rich in sER often appears “empty.” This feature can be seen in sections of adrenal gland (example 1 and example 2).

Compare sER and rER in terms of their appearance in TEM and LM.

The golgi apparatus.