Smooth endoplasmic reticulum (sER) consists of an irregular network of membranous tubes and vesicles lacking ribosomes.

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

• For this reason sER is abundant in steroid-secreting cells of endocrine tissues. Examine sER in Fig. 2-21 for examples of sER.
• Having no associated RNA and little associated protein, sER stains very poorly with routine LM stains and the cytoplasm of cells rich in sER often appears “empty” (e.g. Fig 20-15c and slides 75 and 20).

Compare sER and rER in terms of the shapes of (1) their appearance in TEM and LM and (2) the cell types in which each is particularly abundant.

Cells actively engaged in complex lipid synthesis usually stain poorly in H&E paraffin sections. What is the explanation for this?

The golgi apparatus.