The page contains a brief outlook on the structure of the skin and the functions.

EPIDERMIS:  (There is a diagram further down to help you understand)

This is made up of five layers.

Stratum corneum

Stratum lucidum

Stratum granulosum

Stratum spinosum

Stratum germinativum

The thickness varies all over the body, i.e. the eyelids being the thinnest and the soles of the feet being the thickest.

Stratum germinativum and the Stratum spinosum are the active areas of cell renewal, where as the others are the upper area where cells are changing from living to dead, i.e. a living cell containing nucleus changes to dead horny flat cells with no nucleus.  These are constantly shed from the surface of the skin.

STRATUM GERMINATIVUM – basal layer

The deepest layer of the epidermis, its lower surface is attached to the dermis.  From the dermis it receives nutrient fluid from the blood vessels.  In this layer mitosis (new cells) occurs.  As the new cells are produced the older cells are gradually displaced towards the surface.  Also melanin is formed in this layer, which is the skins natural protection against harmful effects from UV light, it is also responsible for tanning when exposed to the sun.

STRATUM SPINOSUM – prickle cell layer

These cells are immediately above the basal layer.  Nourishment from the protoplasm or tissue fluid is received through fine threads or filaments, which connects the cells.  Keratinization starts in this layer – where a living cell containing nucleus changes to flat cells composed of hard durable protein.

STRATUM GRANULOSUM – granular layer

Cells become flattened, as this is the final stage of keratinization takes place here.  The nucleus begins to disintegrate – loss of fluid that contributes to the transformation of cells into keratin.  This is a tough fibrous protein.

STRATUM LUCIDUM – transparent layer

No nucleus is in these cells, which are transparent packed, small and tight.  Thought to be the barrier zone controlling transmission of water through the skin.  This layer is between the horny layer and the granular layer.

STRATUM CORNEUM - horny layer    

The superficial layer is constantly being shed.  The cells below contain an epidermal fatty substance which helps keep the skin waterproof and prevent the skin tissue from cracking and letting bacteria in which would cause infection.  There are several layers of keratinised cells packed tightly together.

DERMIS:

The dermis is the supportive layer for the epidermis.  The dermis is composed of highly elastic, tough, flexible connective tissue; this creates the contour, strength, elasticity and smoothness of the skin. Being highly sensitive and fibrous, comprised of:

Collagen – provides support to the skin.

Fibroblast cells – these are responsible for manufacturing collagen and a lesser degree of elastin.

Elastin – gives the skin resilience and elasticity.

Also contained:

• Papillary muscles
• Nerve endings
• Blood and lymph vessels
• Hair follicles
• Sweat and sebaceous gland

The dermis having higher water content than other areas of the skin, it also provides nourishment to the epidermis.  The dermis has two layers:

Upper papillary layer:

• Irregular in shape with protrusions into the epidermis called papillae.
• Several nerve endings including: touch, pain, heat, cold and pressure, these have delicate branched nerve endings.
• Fine capillaries – carry away waste products, bring nourishment and oxygen to the skin.  Important and active part of the skin.

Deep reticular layer:

• Found below the papillary layer.
• Tough, elastic collagen fibres interwoven with elastic fibres in this layer.  Responsible for general tone and elasticity of the skin.
• Sweat and sebaceous glands, also the arrector pili muscle, bundles of small involuntary muscles fibres, which are attached to the hair follicles.
• Fine veins and arteries passing through this area, linking up with the papillary capillaries.
• Lymph vessels also form a network through the dermis allowing removal of waste from the skin.

ARRECTOR PILI MUSCLE:

Cold, aggression or fright stimulates this muscle and causing it to contract.  Pulls the hair follicle to and causes the hair to stand up right.  The muscle is attached at and angle to the base of the follicle.

SWEAT AND SEBACEOUS GLANDS:

The Sebaceous glands are situated in the dermis opening into the hair follicle and are found all over the body.  More numerous in the scalp area, on the face particularly around the forehead, chin, cheeks and nose.  The glands secrete sebum, the skins natural moisturiser – can also attract dirt on skin and trapping it there, causing comodones, pustules and papules.  The skin is sometimes also unable to produce enough sebum (asteatosis) causing dry patches and irritation may occur.  When the skin produces excess sebum (seborrhea) the skin takes on a very oily appearance.

Sweat glands (sudoriferous) a tube like duct which rises through the epidermis ending at the skins surface to form a sweat pore, consist of a coiled base emanating from the deeper layers of the dermis.  There are two forms of these;

ECCRINE GLANDS:

Found all over the body, having a duct and a pore through which secretions are brought to the skin’s surface.

APOCRINE GLANDS:

Connected with hair follicles and are found in the areas of; breast, genital and underarm.  The glands secrete fatty substances as well as salt and water, which reacts to the air and causes what is know as body odour.

NERVE ENDINGS:

In the dermis there are several different types of sensory nerve endings, e.g. pain, pressure, heat, cold, touch temperature.  The look of these nerve endings is varied.  Sending messages to the central nervous system and the brain, letting us know what is going on outside the body and the skin surface.

HAIR FOLLICLES:

Downward growths into the dermis of the epidermal tissue.  Found all over the body except on the lips, soles of the feet and the palm of the hands. Each hair follicle has a cluster of cells called germinal matrix at the base.  Reproduce to form lower part of the hair (bulb).  Supplied with nerves and blood vessels.  The hair papillae, nourishes the cells.  Cells move up the follicle from the hair bulb, changing in structure and forming a hair.  The follicle is attached to the base of the epidermis by the arrector pili muscle.

 HYPODERMIS – SUBCUTANEOUS LAYER:

Is thicker in women than in men, that is why women have more rounded contours than men.  Fat is a poor conductor of heat.  As fat is a poor conductor of heat, the hypodermis helps to reduce the loss of heat through the skin and so keep the body warm.  This layer is an area for formation and storage of fat, combination of:

Areolar tissue – elastic fibres, helping to make this layer elastic and flexible.

Adipose tissue – containing fat cells.

FUNCTIONS OF THE SKIN:

Sensory organ

Heat regulation

Absorption

Protection

Excretion

Secretion of sebum

Formation of vitamin D

SENSORY ORGAN:

The skin contains various nerve endings, which can detect: cold, heat, pressure, pain and touch found in various levels of the dermis.

HEAT REGULATION:

When the body becomes warm blood vessels dilate allowing blood to the surface to loose heat.  Sweat is produced through the sweat pore, which cools on evaporation.  When cold the blood vessels constrict and the blood moves slower, hairs erect to trap heat that is near to the surface of the skin.

ABSORPTION:

The skin is able to absorb small amounts of oily substances and some water-soluble substances.

PROTECTION:

Fat cells protect the body against knocks and bangs.

Stratum corneum against injury (abrasions)

Acid mantle against bacteria and fungi

The skin is waterproof so prevents the body from becoming waterlogged and the absorption of invading chemical substances. 

Protects from harmful UV rays from sunshine because melanin is formed in melaloncytes in the basal cell layer.

EXCRETION:

The body (skin) through the sweat pore – 99% water and 1% waster, urea, salt and other impurities.

SECRETION OF SEBUM:

The sebaceous gland secretes an oily substance, which is good for keeping the skin and hair soft and protecting the skin from bacteria.

FORMATION OF VITAMIN D:

Ultra violet rays from the sunshine changes a chemical called “dehydrocholesterol” into vitamin D; this passes into the blood that is important for the growth of teeth and bones (with calcium).