The skin, which forms the outer covering of the body, has a surface area of about 1.5 - 2m2 in adults and it contains glands, hair and nails.
Structure of Skin:
Skin is made up of two layers:
• The epidermis (or, outer covering)
• The dermis (or, true skin)
The epidermis:
The outermost part of the epidermis consists of flat, dead
cells that are constantly being shed The underlying part of the epidermis is made up of rapidly
dividing cells. These are continually pushing upwards and replacing
the dead cells above them. Specialized epidermis cells that extend downwards into
the dermis produce hair and nails, which are also composed of dead
cells. The dermis:
The dermis is made up of tiny blood vessels and nerve endings that are densely woven into the flexible connective tissue. Sweat glands and oil glands are embedded in it.
General Features of Skin:
It is a barrier against germs, and a tough resilient
cushion that protects the tissues underneath, and helps to regulate
the body temperature. When it is hot, glands in the skin secrete sweat, the evaporation
of which causes cooling. Or when it is cold, constriction of the
blood vessels in the skin cuts down the flow of blood near the body’s
surface and so reduces heat loss. Just below the surface of the skin are millions of tiny
nerve endings. These are the touch receptors which tell us about
the world through five different kinds of sensations pain, cold,
heat, pressure and contact The skin supplies much of the body’s vitamin D requirement
by producing substances that changes into vitamin D when it is exposed
to the Ultraviolet radiation in sunlight. The thickness of the skin and the number of special structures
vary in different parts of the body. Skin is thinnest on the lips
and thickest on the scalp, palms of the hands and soles of the feet
(Continual pressure or friction can cause skin to thicken) Hair follicles are found on
nearly the whole body, being abundant on the scalp but absent in
the skin of the soles and palms. Sweat glands, oil glands and
nerve endings are also unevenly distributed. There is a concentration
of sweat glands in the armpits; nerve endings are most abundant
in the lips and fingertips. Skin owes its colour partly to the blood, redness of which shows
through translucent tissues, and partly to various pigments in the
epidermis
