- The skin of vertebrates consists of an outer
layer, the epidermis, which develop from the ectoderm; and an
underlying mesodermal layer known as the dermis. Below the dermis
are deposits of adipose tissue ( fat ).
Skin of man.
- The skin in man varies in thickness from less
than 0.5 mm to 3 or 4 mm in different parts of the
- Under proper conditions the skin is germproof
and serves as an effective barrier against disease organisms. It
is practically impervious to water and under exposure to
ultraviolet rays produces vitamin D.
- The epidermis is arranged in layers of cells.
The most active cells of the epidermis is the single layer of
columnar cells located perpendicular to the dermis. Here these
cells are actively dividing and pushing the previous cells
produced to the surface. This area is called the
germinativium. These cells
eventually reach the surface. They are dead and scaly and leave
the body as flakes. This area is called the stratum
- Keratin, a waterproof protein is found in the
stratum corneum. Keratin is extra thick on the soles of the feet
and the palms of the hands.
- The dermis is
sometimes called the true skin, and is best developed in mammals.
It is not composed entirely of cells but of connective tissue
fibers extending in all directions.
- Dermis is made up of 2 layers. The outer
papillary layer and the
- The epidermis and dermis are arranged in a
mountain valley arrangement. The papillary layer form large
tooth-like projections. This causes the epidermis to filter down
and fill the spaces. This tongue and groove arrangement allows the
skin to be smooth as well allowing it to provide the maximum
amount of friction with a surface.
- Pigment in vertebrates occurs in cells called
is a brown pigment found in these cells.
Melenocytes are found in the lower epidermis of the skin. The cell
loses the pigment as it move toward the surface. In true
albinos there is no skin
- Skin color depends on three factors: skin is
yellow in color, blood vessels give it a reddish hue; the pigment
melanin in different concentrations cause various shades of brown.
The actual amount of pigment is relatively small. It has been
estimated that there is about 1 gram of pigment in the entire skin
of an average Negroid.
- The dermis contains sweat glands, sensory
receptors, lymph glands, blood vessels, nerves, and hair
- Hair grows from the follicle imbedded in the
dermis. A sebaceous gland ( oil gland ) and an arrector muscle are
attached to each follicle. The area above the follicle (hair ) is
an accumulation of dead cells.
- Four factors determine hair color: color of
pigment found in the cortex, amount of pigment, character of hair
surface, amount of air contained within the inner space of the
- Finger nails grow from the root of the nail
just behind the nail under the skin.