SQUAMOUS EPITHELIUM
SKIN:
The multiple functions of the skin are reflected in its
complex structure. Like the
esophagus, it has upward-projecting papillae. The narrow tongues
of the squamous
epidermis that project downward between papillae are called rete
pegs. The squamous
epithelium itself shows a cornified or horny superficial layer of
dead keratinized cells. This
stratum corneum generally has a basket-weave pattern in routine
histologic preparations.
Beneath the epidermis are, from top to bottom, are:
- The papillary dermis - loose connective
tissue carrying vessels and nerves
- The reticular dermis - a layer of heavy, strong collagen
fibers
- The subcutaneous adipose tissue.
The idea of repeating units is helpful in understanding the
skin, not only because of its
regular alteration of papillae and rete pegs, but because the
skin has a regular scattering of
adnexa, or accessory structures. In hair-bearing skin, these are
organized together in the
pilosebaceous unit. It is composed of not only the hair shaft
and the onion-bulb-shaped
sheath of cells which create the protein matrix of hair, but also
the sebaceous gland which
secretes oily substances into the hair follicle and the erector
pili muscle. The eccrine, or
sweat glands, usually lie nearby and empty into their own ductal
system.
|
