Structure and Functions of the Skin

The skin, which is also called the cutaneous membrane, forms a protective, waterproof outer covering for the whole body. The skin plays an important role in providing sensory information of the external environment so the internal environment can adjust and regulate heat , absorption, excretion and secretion.

The skin is the largest organ of the body as it covers the entire surface – an area of between 1.2 and 2 square metres and accounts for approximately 12% of our body weight.  It moulds to and moves with our body.  It is our protective layer to cover our other vital organs.  The skin has to be tough to protect us from constant chemical and physical assault yet sensitive and responsive to subtle changes in the internal and external environment.

With age and sun damage the skin will lose some of its elasticity due to lack of collagen, at which time wrinkles will appear.  The skin secretes an oily substance known as ‘sebum’ which will help to maintain the skin’s suppleness, although there are no sebaceous glands on the palms of the hand or soles of the feet.

The skin is made up of three layers called:

• The Epidermis
• The Dermis
• The Subcutaneous Layer

The main layers of the skin are the epidermis which is a thin portion, followed by the deeper, thicker dermis. This is followed by further layers that lie under the skin; a fatty layer called the subcutaneous fat layer. The dermis is made up of dense connective tissue that is tough and flexible. It contains collagen and a number of structures such as, nerve fibres, blood capillaries, arrector pili muscles, sweat glands and sebaceous glands. Beneath the dermis, lies the subcutaneous fat layer which is composed of loose connective tissue. It helps to anchor the dermis to the underlying tissues and organs.

Watch this video which discusses the cells and layers of the skin you need to know. You may wish to change the playback speed as he talks pretty fast and use the captions! This video also contains some information that you may not necessarily need to know, but it is interesting to watch.

This video covers the functions of the skin:

Sensation – The skin allows us to feel and recognise pain, touch/pressure, and temperature heat and cold. It is covered in somatic sensory receptors which relay these sensations as signals to the brain.

Heat regulation – Vasoconstriction and contraction of the arrector pili muscle to preserve heat, Vasodilation and sweating (via eccrine & apocrine glands) to expel heat and cool the body

Absorption – The skin is capable of absorbing necessary substances, such as nitrogen and oxygen and some medicated creams/essential oils.

Protection – The skin helps to protect us from dehydration, microorganisms/bacteria, injury/trauma, and ultraviolet radiation/sun damage. The skin also carries proteins (keratin) and pigments (melanin). Melanin is what helps to protect against UV rays, the light sensitive pigment ensuring we are not overly damaged by the suns rays. The acid mantle is made from sweat and sebum and provides a protective barrier. The surface of skin is slightly acidic (pH4.5–5.5), which prevents harmful bacteria growing. The skin also protects it’s underlying structures.

Excretion – The skin can also expel uric acid, ammonia, urea, and excess water.  Unwanted human byproducts such as the ones listed above are released through the skin via sweat and sweat glands.

Secretion – Sebum is secreted into the hair follicles and onto the skin.   Sebum contains antibacterial substances to prevent the growth of harmful micro-organisms on the skin’s surface. It also helps to create a barrier against water loss and intake.

Vitamin D – Vitamin D is produced in the skin as a response to exposure to UVB radiation. Cholecalciferol is produced when the sun penetrates the skin, which is taken to the liver where it is made into calcidol and stored as vitamin D.