Rough endoplasmic reticulum (rER) consists of a network of rounded or flattened membranous sacs (cisternae) with polyribosomes covering much of the outer surface of the cisternae (Fig. 2-15). Polypeptides synthesized on these ribosomes are deposited inside the sacs for eventual delivery outside the plasma membrane. Examine the different appearances of rER in Figures 2-14 through 2-17.

Since the RNA associated with rER is basophilic, cytoplasm rich in rER shows basophilia with routine LM stains, such as H&E. This is prominent in neurons, where the basophilic patches in the cytoplasm are called Nissl or chromatophilic substance (Fig. 9-3 and slide 71). Basophilic rER is also prominent in secretory cells, where it is sometimes called ergastoplasm. An example of this occurs near the nucleus of cells in the pancreas (Figs. 2-23 and 16-9 and slide 154).

What is the difference between the functions of free polyribosomes and polyribosomes on rER?

Why is Nissl substance more prominent in actively growing neurons?

Smooth endoplasmic reticulum.