(C20-22) Slide 194: Finger tip and nail.

This fingertip is from a child, and it is shown at low-power in C20. It is particularly useful for its demonstration of the structures found in the dermis. The epidermis is not as well developed as in the adult and the layers are not obvious. The vasculature is especially well preserved. Notice the venule leading from a capillary loop in each one of the dermal papillae (C21, arrow). These papillae are actually ridges which interdigitate with valleys in the epidermis, and together give rise to fingerprints and the whole system of ridges that is visible on our palms and soles. As one goes deeper in the dermis and hypodermis, the caliber of the vessels rapidly increases. Deep in the dermis, between the palmar side of the tip and the bone, there are several Pacinian corpuscles cut in different orientations (C22P). There are also sweat glands (arrow), and you should be able to distinguish both parts of this simple, coiled, tubular gland. The secretory portion stains more lightly, while the duct portion stains more darkly. The lumen of the gland is obvious in the secretory portion, and it is surrounded by a low columnar epithelium. At the base of these secretory cells are the small, very condensed nuclei of myoepithelial cells; the duct lumen appears to be closed. Notice that the ducts run up very often to the bottom of the valleys of the epidermis. The slide is an excellent place to review endochondral bone formation.