|
The 3 skin layers: epidermis, dermis, subcutaneous fat
The skin is made up of three distinct layers.
The top layer is called the epidermis.
(The word epidermis, and the name of the other main skin
layer, the dermis, both come from the name used by the ancient
Greeks for the skin, derma. From this we also get the word
dermatologist, meaning a doctor who specialises in skin problems.)
The epidermis is translucent. That is, it
allows light to pass partially through it, rather as frosted glass
does. The epidermis does not contain any blood vessels but gets
its oxygen and nutrients from the deeper layers of the skin.
At the bottom of the epidermis is a very
thin membrane, called the basement membrane, which attaches
the epidermis firmly, though not rigidly, to the layer below.
The second layer lies deeper and is called
the dermis. It contains blood vessels, nerves, hair roots
and sweat glands.
Below the dermis lies a layer of fat, the
subcutaneous fat. The depth of this layer differs from one
person to another. It contains larger blood vessels and nerves,
and is made up of clumps of fat-filled cells called adipose cells.
The subcutaneous fat lies on the muscles
and bones, to which the whole skin structure is attached by connective
tissues. The attachment is quite loose, so the skin can move fairly
freely. If the subcutaneous tissues fill up with too much fat the
|
|
areas of attachment become more obvious and the skin cannot move
as easily -this is what gives rise to the notorious cellulite
(see pages 32 and 34).
The junction between
the epidermis and the dermis is not straight but undulates like rolling
hills - more markedly so in some areas of the body than others. A
series of finger-like structures called rete pegs project up
from the dermis, and similar structures project down from the epidermis.
These projections increase the area of contact between the layers
of skin, and help to prevent the epidermis from being sheared off.
They are not present in the skins of unborn babies but rapidly develop
after birth, and are very noticeable in a young person's skin when
it is examined under the microscope. As skin ages they get smaller
and flatter.
Networks of tiny blood vessels run through
the rete pegs, bringing food, vitamins and oxygen to the epidermis.
In pale people these vessels can be seen through the epidermis, particularly
if the veins widen (so-called 'broken veins'). If the blood carries
plenty of oxygen it will be pink and the skin will tend to have a
rosy color. If the blood is running sluggishly and has lost most
of its oxygen the skin will look bluer. These blood vessels respond
to temperature changes. They open up in hot weather, bringing lots
of red blood cells - and hence a pink flush -to the skin, and close
down in the cold; this is why cold skin often looks blue.
(continued on next page) |
