Slide 79 - Thick skin. So called because its epithelium is thick.  The epithelium is stratified squamous and is heavily cornified (keratinized).  Such skin is found on the palm of the hand and the sole of the foot, where wear is greatest.  There are five distinct layers in this epithelium, beginning with the basal one:  (1) the stratum germinativum (stratum basale) with its cells lined up very regularly, (2) the fairly thick stratum spinosum with intercellular bridges, (3) the dark stratum granulosum with is purple keratohyalin granules, (4) the translucent, closely packed stratum lucidum, and (5) the dried, scale-like stratum corneum.

How would you distinguish this epithelium from the stratified squamous epithelium of the esophagus?  Why is this epithelium called squamous?

By what mechanism is the epithelium replenished as the dead cells of the corneum are sloughed off?  In which layer do the cells of the epidermis begin to die?

What are keratinocytes?... prickle cells?... basal cells ... dendritic cells ?  Look for yellow-brown melanin in the cells of the stratum basale; what cells produce the melanin?  What are melanosomes?

In EM where would you find desmosomes particularly well developed?   ...or hemidesmosomes?  What are tonofilaments?...where would you find lamellar granules?

            In the connective tissue dermis beneath the epithelium look for:

            1.     dermal papillae indenting the basal epithelium

            2.     possible Meissner’s corpuscles (sensory endings for touch lying in dermal papillae)

            3.     ducts from sweat glands leading to the surface

            4.     a fairly loose, cellular, usually quite thin papillary layer of connective tissue immediately underlying the epidermis

            5.     a thick, more fibrous reticular layer of connective tissue

            6.     sections of small nerves and blood vessels

In the subcutaneous layer:

            1.     both adipose tissue and irregular, fibrous connective tissue

            2.     larger nerves  and blood vessels

            3.     coiled, secretory portions of sweat glands (seen as multiple X-cuts of tubules).  Look for myoepithelial cells.

            4.     possible Pacinian corpuscles (sensory endings for pressure)