s k i n p h y s i o l o g y
Keratinization takes place on all exposed
skin surfaces except the cornea of the eye.
On the exposed surface of the skin these
keratinocytes remain tightly interconnected by
intercellular connections called desmosomes.
This interconnectedness makes this layer water-
resistant. Normally keratinocytes remain in
the stratum corneum for about 28 days before
they are shed.
The squamous cells within this layer protect
the layers below the stratum corneum. The
main function of squamous cells is protection.
The stratum corneum also protects the skin's
moisture balance by acting as a barrier to
When the protection of the underlying tissue
is destroyed, for example in the case of a
second-degree burn, the skin is greatly injured
and its ability to protect the body from infection
is hindered. This is because the skin's moisture
barrier and protective barrier are destroyed.
The stratum lucidum layer is found throughout
the body but is thickest on the palms of the hands
and soles of the feet. The stratum lucidum is a
transparent layer that lies between the stratum
corneum and stratum granulosum. The
keratinocytes of the stratum lucidum contain
densely packed clear keratin. These thick skin
areas are where epidermal ridges or whorls are
located that provide your palms and soles with
traction. You can grasp things with your hands
more easily because of these ridges, and they cause
friction so you don't slip when walking barefoot.
These genetically determined ridges on your
fingertips are fingerprints, which have been used
for more than a century in crime detection. Your
fingerprints are unique and consistent; they do not
change as you age. At the time of your birth, ink
prints were probably made of epidermal ridges on
the soles of your feet for identification purposes.
Did you know that the skin is thickest on the
palms of the hands and soles of the feet, and
thinnest on the eyelids? To help you remember
the differences in thickness of the skin, think of
the palms of the hands and soles of the feet as a
brown paper bag; facial skin as a piece of notebook
paper; and the eyelids as tissue paper.