The Skin

Skin, is the body’s largest organ. It’s main job is to protect your body against the stresses of the environment and to control the body’s temperature. Skin is in fact the only organ that comes into direct contact with the outside world.

The skin is made up of 3 main layers. Epidermis, dermis and subcutaneous layer

Epidermis
Consists of 3 parts. Stratum corneum (horny layer), Keratinocytes (squamous cells)
and the basal layer.

Stratum corneum (horny layer)
Is the uppermost layer of skin and prevents the entry of most foreign substances from entering the body. This also protects the loss of fluid from the body. The outer layer is constantly being shed.

Keratinocytes (squamous cells)
Contains keratinocytes, (living cells). These are fed to the horny layer when they are mature. These contain the protein keratin, which is a substance that adds strength to the outermost layer of the skin. (this is where a form of skin cancer begins - squamous cell carcinoma )

Basal layer
The deepest layer of the epidermis, is in direct contact with the dermis and contains basal cells. Basal cells continually divide forming new keratinocytes which are then fed towards the outer layers. (basal cell carcinoma, another form of skin cancer begins here)

The basal layer also contains another type of cell called ‘melanocytes’. These cells produce melanin, which is a pigment that is the source of tanning. People of all races contain approximately the same number of melanocytes, however, people of different races will produce different levels of melanin.
The most dangerous form of skin cancer – melanona – begins here.

Dermis
The dermis contains hair follicles, sweat glands and nerve endings that allow you to sense the world. Pain and touch receptors act as a warning that something may be damaging your skin. The dermis is held together by the proteins collagen and elastin. Collagen accounts for upto 75% of the weight of the dermis and is responsible for the elasticity of the skin. The dermis also helps to control the body’s temperature.

Subcutaneous Layer
This is the deepest layer of the skin. The subcutis contains a network of collagen and fat cells that act as a ‘shock absorber’ to help protect the body from injury. They also help to conserve the body’s heat. Blood vessels branch infinitely from the subcutis into the dermis, unlike the epidermis which has no direct blood supply.

Skin types – for exposure to ultraviolet light
(developed by Dr. Thomas Fitzpatrick – Harvard Medical School)

Fitzpatrick Prototype