The skin is made up of three layers called:
The epidermis is the upper portion of the skin and consists of five layers:
• Horny layer (stratum corneum)
Outermost layer of the epidermis, made up of several layers of flattened, mostly dead overlapping cells. These cells help to reflect UV light.
Black skin, which evolved to withstand strong UV light, has a thicker stratum corneum than Caucasian skin. It takes about 3 weeks for the epidermal cells to reach the stratum corneum from the stratum germinativum. The cells are then shed through a process called desquamation.
• Clear layer (stratum lucidum)
This layer is only found in thicker areas of the skin such as the palms of the hands or the soles of the feet.
Found below the horny layer and consists of dead keratinized cells without a nucleus. The cells are transparent, which allows the passage of sunlight into the deeper layers.
• Granular layer (stratum granulosum)
In this layer the cells being to die. These cells have what looks like granules within them caused by the nuclei breaking up. These granules are known as kerathohyalin granules and later form keratin.
• Prickle cell layer (stratum spinosum)
Made up of cells which have a spikey surface to connect with surrounding cells.
This is the layer that begins to synthesise keratin.
In this layer the cells are living. Pigment granules called melanin may be found here.
• Basal layer (stratum germinativum)
Column shaped cells responsible for producing new epidermal cells. Cells divide and move up to higher layers. The remaining cells divide to fill the gaps. This process of cell division is caused mitosis.
As the new cells are produced they push older cells above them towards the surface of the skin, until they finally reach the horny layer. It takes 3 – 6 weeks for the skin cells to be pushed up from the basal layer to the horny layer.
• Germinative Zone
This zone is the epidermis contains two other important cells – Langerhans and Melanocyte cells.
Langerhans cells absorb and remove foreign bodies that enter the skin. They move out of the epidermis and into the dermis below, then finally enter the lymph system – the body’s waste disposal system.
Melanocyte cells are responsible for the production of melanin in the skin. These protect the other epidermal cells from the harmful effects of UV. Melanin helps determine our skin colour; the more melanin present, the darker our skin tone.
The dermis lies below the epidermis, and connects with the basal layer and is often described as the “true skin”. It is responsible for the strength and elasticity of the skin. It contains lots of specialised cells and structures, including nerves, blood vessels, glands and hair follicles.
It consists of two layers:
• Papillary layer
This is the upper section and contains small tubes called capillaries, which carry blood and lymph. It also has nerve endings. This layer provides nutrients for living layers of epidermis. It contains a thin arrangement of collagen fibre.
• Reticular layer
Consists of two types of protein:
- Elastin fibres which give the skin its elasticity
- Collagen fibres which give the skin its strength
These fibres are held in a gel-like substance called ‘ground substance’. The collagen and elastin fibres form a strong network which gives us our youthful appearance.
As we age, these fibres in the skin begin to harden and fragment; the network starts to break down and our skin starts to lose its elasticity and show visible signs of ageing. Blood circulation to the skin declines; nutrients do not reach the surface, resulting in sallow skin. The fatty layer beneath the skin grows thinner so we look more drawn as our bone structure is more prominent. The reticular layer is vital to our skin’s health and appearance and so it is essential that it is looked after in order to prevent signs of ageing.
The subcutaneous layer is situated below the dermis. It consists of adipose tissue (fat) and areolar tissue. The adipose tissue helps to protect the body against injury and acts as an insulating layer against heat loss, helping to keep the body warm. The areolar tissue contains elastic fibres, making this layer elastic and flexible. Muscle is situated below the subcutaneous layer and is attached to bone.