HA14-17: Finger, monkey - toluidine blue
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The epidermis of the finger is an extremely thick, keratinized stratified squamous epithelium ( HA14 ). The epidermis is much thicker on the ventral surface (palm) than it is on the dorsal surface ( HA17 ), because the ventral surface is subjected to much more abrasion than is the dorsal surface.
At high magnification ( HA 15 ), look more closely at the epithelial cells. While cells in the basal half of the epithelium have nuclei (clear central areas with small dark spots), cells in the apical half of the epithelium are enucleated and dead, making this a keratinized epithelium. In the intermediate layers, where the cells are alive, the cells look spiny (HA16) . The spines are spot desmosomes that are holding the cells together. You may recall that spot desmosomes are one component of the junctional complex, but they are also found outside junctional complexes where they connect epithelial cells to each other, especially in stratified epithelia. For review, what are the dark spots in the clear nuclei in HA16? What is their function? What would you expect to be a major filamentous protein synthesized in these cells?
The epidermis on the dorsal surface of the finger is much thinner and it lacks the layering seen on the ventral side ( HA15 ). However, it has other interesting features, including sebaceous glands and hair follicles, that extend into the subjacent (underlying) connective tissue (HA17) . The secretory cells of sebaceous glands are distinctive because of their foamy looking cytoplasm. The cells fill with sebum, die and the entire cell is shed during holocrine secretion. These exocrine glands must use ducts to deliver their secretory product. Sebaceous glands always use adjacent hair follicles as their ducts; whether or not that is obvious depends on the plane of section. What are the two other methods of exocrine secretion?