1-25 Basic concepts

STAINS FOR LIGHT MICROSCOPY – 3

Several types of cells, especially those that synthesize many proteins, have many free ribosomes in their cytoplasm or a highly developed rough endoplasmic reticulum (RER). The cisternae of RER are ususally asssociated with many ribosomes which contain RNA. Cells that have large sets of RER cisternae, and clusters of these cisternae can be seen in sections under a light microscope and are called ergastoplasm.

The cytoplasm regions of cells that have many ribosomes stain in blue by hematoxylin. It has already been mentioned that the affinity of acidic structures for basic dyes is called basophilia. Therefore, these regions of the cytoplasm are called basophilic.

A very demonstrative example of cytoplasmic basophilia can be seen in the exocrine cells of the pancreas. These cells secrete pancreatic juice, which is made up of a large amount of proteins. The general shape of these cells is pyramidal or pear-shaped. They are grouped into small spherical clusters called acini (more details about these glands in the chapters “Glandular Epithelia” and “Pancreas”).

The region of the acinar cells that contains the greatest amout of ribosomes is placed at the base of the pyramid (the “ergastoplasm”, rough endoplasmic reticulum). As these cells contain many proteins alongside nucleic acids, this region stains with a mixture of hematoxylin and eosin, furnishing thus a purple color.

As you move the mouse or click on the figure, two exocrine cells of an acinus appear demarcated by dark lines. The basophilic portion of their cytoplasm will appear in light blue. A few nuclei of acinar cells will appear shaded in a darker tone of blue.
The region of the cell that occupies the superior region of the pyramidal cell, also called “apical region”, is filled with secretory grains – which contain pancreatic juice. They is made up almost entirely of proteins, which are preferentially stained by acidic dyes such as eosin – this region is therefore acidophilic (or eosinohilic).
The apical region two acinar cells will appear pink after you place the mouse or click on the image.

Take the opportunity to observe that these secretory cells have very large and prominent nucleoli, highlighted in some of the nuclei.