As you have been examining the nuclei of cells, you have surely noticed that (in addition to nucleoli) they do not stain uniformly.

Light-staining areas of the nucleus are called "euchromatin". Abundant euchromatin denotes an active cell.

Dark-staining areas of the nucleus are called "heterochromatin". There is always a rim of heterochromatin under the real nuclear membrane. Abundant heterochromatin with only scanty euchromatin denotes an inactive cell.

This is a section of the epidermis, the epithelial covering of the skin. It is a self-renewing structure and metabolically quite active, so its nuclei feature. However, they display heterochromatin under their nuclear membranes, and little patches of heterochromatin throughout their nuclei.

The patches of heterochromatin are much smaller than the nucleoli, and stain more blue, the same color as the heterochromatin at the outer edge of the nucleus.

With your study partners, find:

• the cell borders


• the nuclei


• the nucleoli (there may be more than one visible in a cell)


• the rim of heterochromatin under the nuclear membranes


• the stippled pattern of euchromatin and heterochromatin in the nuclei


• a mitotic figure

We can't really mark the heterochromatin chunks in the nuclei; they're too small. We don't think you'll have trouble identifying them.

United States Pronunciations:

• Euchromatin: YOO-chrome-uh-tin


• Heterochromatin: HETT-err-oh-CHROME-uh-tin

Roots:

• eu: good


• hetero: the other

Hotshots:

Did you notice that the epidermal cells are connected by a series of little junctions, like railroad ties? These are the "prickles" or "spines" of the epidermis. Actually, they are desmosomes. Fixation in formalin has pulled the cells slightly apart.