Thick skin is found on fingertips, palms and soles of feet. It is specialized for protection during friction and contains sensory receptors responsive to pressure, the Pacinian corpuscles. Thin skin covers most of the body and is similar in many respects to thick skin. For example, thin skin contains hair follicles but does not have Pacinian corpuscles to respond to pressure and friction. .

Examine a section of thick skin and identify epidermis and dermis.

• In the dermis, note the difference between the papillary and reticular layers.
• Note too how downward epidermal folds or ridges interdigitate with upward projecting dermal papillae.
• In the epidermis, identify characteristic cells, keratinocytes, (as seen in Fig. 18-2) 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 do the small “spines” on keratinocytes of the spinous layer represent?

What is contained in the granules of the keratinocytes of the granular layer?

Since the cells there are dead, why is the cornified layer so critically important?

How does melanin get from the melanocytes into the keratinocytes?

List several functions of the dermis and hypodermis.

The skin as a route of medication delivery.