Thick skin -- present on fingertips, palms, and soles of feet, it is specialized for protection during friction and contains sensory receptors responsive to pressure, the Pacinian corpuscles.

Examine a section of thick skin (slides 5, 7T and 89) and identify epidermis and dermis (Fig. 9.1 and 9.17).

• In the dermis, note the difference between the papillary and reticular layers.
• Note too how downward folds or ridges of epidermis interdigitate with upward projecting papillae of dermis.
• In the epidermis, identify characteristic cells, keratinocytes, (as seen in Fig, 9.2) representing the
  • Stratum basale,
  • Stratum spinosum,
  • Stratum granulosum, and
  • Stratum corneum
  • Click image to right for expanded view.
• The strata grade into one another and cells gradually move outward from the basal layer to the cornified layer.

What is the structural significance of the small “spines” on the cells of the spinous layer?

Study the ultrastructural features of cells of the various epidermal strata (Figs. 9.3 and 9.4).

Describe the cell biology of the keratinization process, accounting for all the histological features seen.

The skin as a route of medication delivery.