The-Skin-Notes.(1)
                     Chapter Two The Skin
The largest organ of the body. It provides a protective layer covering underlying structures of the body. It is 
the bodies first line of defence against bacteria - it prevents them entering the body.
3 main areas:
1. The Epidermis - surface of the skin (5 layers)
2. The Dermis - supports the epidermis and provides shape and elasticity
3. Hypodermis/subcutaneous layer - made of adipose tissue, muscles and blood vessels.
The Epidermis
Superficial layer of stratified epithelium. It does not have its own blood supply. Its thickness varies - thinnest 
on eyelids and thickest on the soles of the feet. There are five layers.
The top 3 layers are dying - turning from living to dead cells.
The bottom 2 layers are alive and active. Cell renewal occurs here.
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Stratum germinativum (Basal cell layer)
Deepest layer of the epidermis. Lower surface is attached to the dermis. Dermis supplies it with nutrients.
Mitosis occurs here. Cells born here are pushed up into the next layer.
Melanocytes are also found here. These are cells that produce the pigment melanin. This is the skin’s natural 
protection from UV rays.
Stratum spinosum (Prickle cell layer)
Next layer up containing living cells and also langerhan cells. These are cells that engulf foreign particles to 
protect the skin. All cells in this layer are connected to each other by filaments. On the upper most layers of 
this section, keratinisation begins. This is the change of living cells containing a nucleus into layers of flat cells 
composed of a hard durable protein called keratin.
Stratum granulosum (Granular layer)
Cells from below have pushed up and are becoming flattened and full of keratin giving them a ‘grainy’ 
appearance. The nucleus dies = cells die.
Stratum lucidum (Clear layer)
At this stage all the cells are filled with keratin and therefore look clear as opposed to ‘grainy’. No nucleus is 
found here in any of the flattened cells. It is very evident in thick areas of skin (soles of feet). It is said to be 
very important in controlling the passage of water through the skin.
Stratum corneum (Horny layer)
Several layers of keratinised epithelial cells packed tightly together. Keratin has made them tough, dry, no 
nucleus and horny. The superficial layers are constantly being shed by a process known as desquamation.
The cells below have a fatty substance that helps to prevent the skin from drying out and keeps it waterproof.
The Dermis
Made of dense connective tissue that is tough, elastic and flexible. It gives strength, shape, elasticity and 
smoothness to the skin. It is highly sensitive and consists of:
 Collagen - protein collagen makes these white fibres. They run in parallel bundles with each other. Gives 
the skin strength and shape - they are inelastic but flexible.
 Elastin - protein elastin makes up these yellow fibres. These are thinner than collagen fibres and are very 
elastic. They give the skin its elasticity.
 Fibroblasts - these are cells that produce collagen and elastin fibres. Found in the dermis of the skin.
 Mast cells - these produce heparin to thin the blood and histamine that is released during an allergic 
response. These cells are found very close to blood vessels.
 Plasma cells - these cells produce anti-bodies to foreign particles, so help to fight infection in the skin.
It has a lot of water and provides nourishment to the epidermis to help keep the cells in the basal cell layer 
alive and reproducing.
It has 2 main areas:
1. Upper papillary layer: this layer is below the epidermis and the upper part of the dermis (1/5 th of 
total dermis depth). It runs between these 2 in a wave-like manner with protrusions into the 
epidermis called papillae. Capillaries are found here delivering oxygen and nutrients to the skin and 
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carrying away waste. Also nerve endings are found here sensitive to touch, cold, heat, pressure, 
pain.
2. Deep reticular layer: This layer provides elasticity and tone to the skin. It contains collagen and 
elastin fibres. Sweat and sebaceous glands are found here and other appendages of the skin. Many 
fine arteries and veins pass through here which connect up with the papillary capillaries.
Appendages of the dermis
1. Specialised cells – Fibroblasts, Mast cells, Histiocytes, Leucocytes
2. Nerve endings - pick up on pain, heat, cold, pressure, touch.
3. Hair follicles - travel from deep in the dermis up through the epidermis via an opening. Tiny erector pili 
muscles are attached to help the hair to ‘stand on end’ and create goose bumps.
4. Sweat glands - eccrine produce a water + salt sweat for body temperature control. Found in non-hairy 
parts of the body. Apocrine produces a thicker sweat of water + salts + fatty acids + waste and this 
produces body odour. Found in hairy parts of the body, attached mainly to hair follicles.
5. Sebaceous glands - connected to hair follicles. Not found on palms or soles. Produce sebum, a protective
oily film on the skin. It forms the acid mantle and is the skin’s natural moisturiser. It prevents the 
skin from drying out. But it attracts dirt and this can cause blackheads, papules and pustules to form. Dry
skin is when little sebum is produced and irritation can occur. Overproduction of sebum is called 
seborrhoea. 6. Blood vessels - blood capillaries feed up through the dermis but are not found in the 
epidermis. They deliver oxygen and nutrients to the skin and remove waste products.
7. Lymphatic vessels – work in conjunction with blood supply to carry waste products away from area.
8. Papilla - a little projection at the base of hair root that contains blood capillary and nerve to keep the 
hair alive.
The Hypodermis
An area where fats are made and stored. It is made of adipose tissue (energy reserve, support and protection)
and areolar tissue (loose with collagen, elastin and reticular fibres). The hypodermis helps to insulate the body
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by preventing loss of heat through the skin.
Functions of the Skin
Secretion - of sweat and sebum. Sweat removes waste from the skin and also helps control body 
temperature. Sebum from the sebaceous glands is a natural moisturiser and waterproof layer for the skin. 
The mixture of sebum + sweat on the skin surface = acid mantle. A protective layer against bacteria.
Heat regulation - the skin allows the body to either lose heat or retain it. It does this through the blood that is
flowing in the blood vessels. Vasoconstriction is when the blood capillaries tighten up to stop blood from 
reaching the skin surface. It happens if the body is cold. If no blood is getting to the skin surface, then no heat
will be lost by radiation, conduction or convection. Vasodilation is when the blood capillaries relax and allow 
a lot of blood to reach the skin surface. This causes the skin to flush and heat is lost by radiation, conduction 
or convection. The body is also able to promote shivering to increase body temperature.
Absorption - the skin cannot absorb a lot of substances as it is a waterproof layer. Essential oils, drugs and 
some conditioning creams can be absorbed via pores and follicles in the epidermis.
Protection - the skin is a natural layered barrier against entry of bacteria etc. It also has the protective acid 
mantle to stop microbes growing on the skin surface. The pigment melanin protects us against burning UV 
rays of the skin. Langerhans cells protect us from infection and boost the immune system. Nerve endings give 
us warning signs of extremes and danger. Waterproof layer prevents the loss of essential body fluids.
Elimination - toxins such as salts, urea and waste water are lost through sweat glands of the skin.
Sensation - the nerve endings and other receptors of the skin can detect pain, cold, heat, pressure and touch. 
Different receptors lie at different levels in the skin.
Vitamin D production - sunlight converts a substance called ergosterol found in sebum into Vitamin D. 
Vitamin D is essential for calcium and phosphorus absorption for healthy teeth and bones. A lack of vitamin D
leads to rickets in children.
Melanin production - UV rays from sunlight causes an increase in natural skin pigment melanin to be 
released. This pigment absorbs the damaging rays of sunlight and protects us from burning and damage.
Disorders of the Skin
Congenital
 Eczema: The skin in any area of the body can become dry, itchy, flaky and cause great discomfort. 
Bleeding and oozing will occur due to itching. Common areas for eczema are elbows, behind knees, face,
hands, scalp. Causes may be endogenous or exogenous. It is not contagious.
 Psoriasis: A chronic inflammatory disorder of the skin. It is characterised by areas of red patches covered
with silvery scaling skin. Bleeding, oozing, irritation and itching occurs. Can be very sore and irritating 
and can be found anywhere on the body. There is no ‘cure’. It is not contagious.
Bacterial
 Acne vulgaris: This starts out as a hormonal imbalance that causes excess sebum to be produced. This in 
turn attracts dirt and promotes bacterial infection. The result is blocked pores, blackheads, papules, 
pustules and marked skin. Pitting and scaring can result. Main areas affected are the face, neck, back, 
chest and shoulders. It is not contagious.
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 Acne rosacea: This occurs on the face and neck and starts out as an irritation due to factors such as diet, 
hormones, environment changes, alcohol, etc. This results in vasodilation of surface blood capillaries and
reddened appearance. This leads to raised papules, pustules and erythema. It is not contagious.
 Folliculitis: This is a bacterial infection of the pilo-sebaceous duct (sebaceous gland + hair follicle). It 
causes redness and inflammation. It is connected with acne vulgaris and hormonal imbalances.
 Boils (furuncles): This is a bacterial infection of the skin, causing an infection locally around a hair follicle.
Can be contagious - mostly not.
 Impetigo: A bacterial infection caused by the bacteria staphylococcus aureus from the nose. It is found 
mainly on the face area and causes blisters that ooze and form a yellow crust. This is highly contagious.
Viral
 Warts: Small horny tumours on the skin caused by a viral infection - Highly contagious.
 Verruca: ‘Plantar warts’. These are warts found only on the feet. They appear more spread out and ‘see 
through’ with a small black dot in the centre. They are highly contagious.
 Herpes Simplex (HSV): This is an infection known as the ‘common cold sore’. They can be found on the 
mouth, cheeks, chin and other body parts. Red area with small blisters. Highly contagious.
 Herpes zoster: A viral infection known as the ‘shingles’. This is the adult form of chicken pox. It affects 
the spinal nerves and is extremely painful. Can take up to 2 years to recover. Highly contagious.
Fungal
 Tinea pedis: ‘Athletes Foot’. This is an infection caused by the presence of fungus, found on the feet and 
between the toes. Fungal infections thrive in warm, moist and dark conditions. They attach themselves 
onto and live off the keratinised skin cells. Causes redness, itching, bleeding, white peeling skin. Highly 
contagious and can be moved from the feet to other parts of the body.
 Tinea corporis: Fungal infection of the skin on the body. It is the ‘common ringworm’ that appears in a 
red circle on the skin and spreads out. Highly contagious.
 Tinea ungium: Fungal infection of the nail. Highly contagious.
Infestations
 Scabies: An animal parasite that burrows beneath the skin and invades the hair follicles. Tiny papules 
and grey lines appear. Secondary bacterial infections can occur. Highly infectious.
 Pediculosis: Lice. Pediculosis capitas (headlice). Pediculosis pubis (pubic lice). These are animal parasites 
that infect the hair. They bite onto the skin and draw blood to survive. They lay eggs. When the eggs 
have hatched, the empty shell oxidises and looks white - these are the nits. Highly contagious.
Pigmentation (not contagious)
 Vitiligo: A complete loss of colour in well-defined areas of the body. It is a form of leukoderma. The 
melanocytes stop producing melanin. It is more obvious in darker skins. White patches may start small 
but develop and merge.
 Albinism: This is a genetic/inherited disorder where there is a complete lack of melanocytes, therefore,
the pigment melanin cannot be produced. People are very photosensitive.
 Chloasma: This is hyper-pigmentation normally seen as a butterfly mask on the face. Due to hormonal 
changes or imbalances - e.g. pregnancy, contraceptive pill.
 Ephelides: Freckles. Small pigmented areas that become darker on exposure to the sunlight.
 Lentigo: Liver spots are darker than freckles with a slightly raised appearance.
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 Papilloma: Moles. Pigmented areas of the skin found in varying parts of the body. Sessile moles are flat. 
Pedunculated moles are raised.
 Naevae: Birthmarks are areas of pigmentation (light to dark) found in different parts of the body. 
Some are associated with strong hair growth. Strawberry naevae are found on babies and are a pink 
colour. They normally disappear as the child grows.
 Port wine stains: Larger areas normally of dilated capillaries. Colour can vary from pink to dark red. They
are commonly found on the face.
General (not contagious)
 Broken capillaries: Dilated capillaries on fine skin, normally seen on the face. Ruptured blood vessels can
become bulbous and blue if congested. Due to irritation and stimulation.
 Crows feet: Fine expression lines around the eyes - ‘laughter lines’.
 Urticaria: Hives, nettle rash. An allergic reaction to some stimulant. Characterised by weals/welts of 
pink colour. Very itchy and can lead to secondary bacterial infection.
 Comedones: Blackheads. Due to build-up of sebum and dirt on the skin and pores. The sebum is 
oxidised and gives the colour. Common with acne vulgaris.
 Milia: Whiteheads. When sebum becomes trapped in a duct with no opening/below the epidermis.
Common on the orbicularis oculi muscles areas around the eyes.
 Dermatitis: Allergic reaction to being in contact with some irritant like shampoos or detergents (contact 
dermatitis).
 Seborrhoea: Excessive oiliness due to hyperactivity of the sebaceous glands. Caused by hormonal 
imbalances.
Skin Cancer
Non-melanoma cancers: more common in women than men
 Basal cell carcinoma: Tumours arise in cell of the stratum germinativum of the epidermis. They 
rarely metastasize (spread). Usually on face, nose, eyelids.
 Squamous cell carcinoma: Tumours arise in the squamous cells of the epidermis. Most arise from pre-
existing lesions or damage due to chemicals, sun-exposure, etc. Some metastasize, others don’t.
Melanomas
 Malignant melanomas: Arise from melanocytes in the epidermis. Can develop from a previously 
benign mole. They metastasise rapidly.
Key to early detection of melanomas
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A ASYMMETRY B BORDER C COLOUR D DIAMETER
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