The skin is the largest organ of the body and with the
exception of the brain, probably the most complex. It wraps the adult
body in about 20 square feet of tissue, weighing some seven pounds.
The skin can be very sensitive or very tough. Human skin is furrowed
by ridges and valleys, pitted with tunnels from which hair tips project,
moistened by salt water and lubricated by an invisible moving film of oils.
The skin is a layered organ. The outer skin or epidermis,
has several anatomical layers. The topmost horny layer is composed
of dead cells that are always being worn off. We shed our skins continuously,
not all at once as reptiles do. Beneath the epidermis is the dermis.
It contains connective tissue, is strong and elastic, and is the part of
animal skin that makes leather when tanned. It is laced with blood
vessels, nerve fibers, receptor organs for sensations of touch, pain, heat
and cold. Beneath the dermis is a layer of tissue with fatty elements that
help cushion the skin above it.
Our skin is equipped with upward of two million tiny glands which
excrete fluids well known as sweat or more generally as perspiration.
We have about as many oil secreting glands in the skin as we have sweat
glands. Most of these occur in or near hair follicles.
Hair is a modified form of skin cells and so are fingernails
and toenails. Hairs grow in almost the entire skin, though in many
areas they are so inconspicuous that they are never noticed.
- Students should complete the worksheet on the skin so
they can see all the different layers. You may want to tell students that the
color pigments of our skin are only on the first layer. The pigment melanin,
is responsible for the darkening. The pigments are there as an evolutionary
reaction to being out in the sun for a long time. The darker the skin the more
that person's ancestry was exposed to the sun (this is a simple explanation.)
Answers: 1=fat cells; 2=papilla; 3=nerve ending;
4=sweat glands; 5=oil secreting glands; 6=shaft; 7=epidermis; and
- Making fingerprints is relatively easy. Using an ink
pad, have the students roll the tip of their fingers on the pad. Then have
them roll it on the sticky part of tape. Then put the tape (sticky side down)
a paper, so you can easily view it with your microscope or hand lense.
Instruct students to compare their fingerprints with a partner's and have them
determine how they differ.