Skin e-book Flashcards
The skin has many functions:
• Regulate body temp
- Thermoregulation through sweat
• Store blood
• Protect the body from the external environment
- Micro-organisms, dehydration, UV light, trauma
• Detect cutaneous sensations
- Touch
- Pressure
- Vibration
- Tickling
- Warmth
- Coolness
- Pain
• Excretion and absorption
- Water soluble substances not greatly absorbed
- Some lipid soluble substances absorbed – vitamins A, D, E, K, oxygen and carbon dioxide, drugs (e.g. steroids)
- Some toxic materials absorbed – organophosphates, acetone, lead, mercury, arsenic salts
• Synthesis of vitamin D
What is the epidermis made up of
- Approximately 90% of the epidermis is made up 4-5 layers of keratinocytes.
- Approximately 8% of the epidermis is made up of melanocytes.
Role of keratinocytes
These cells produce keratin, a substance that protects the skin and other tissues from heat, microbes and chemicals. The keratinocytes also produce lamellar granules.
Role of lamellar granules
These release a water repellent sealant to decrease water loss from the skin and water absorption through the skin. The sealant also inhibits the entry of foreign material through the epidermis.
Role of melanocytes
These cells produce melanin which is absorbed by the keratinocytes. The melanin granules absorbed by the
keratinocytes cluster around the cell nucleus on the skin surface side and protect the DNA contained within from UV light
What are the remaining cells that make up the epidermis
Langerhans cells and Merkel cells
Role of langerhans cells
Langerhans cells are antigen presenting cells of the immune system and their function is to recognise antigens and present them to other immune cells for recognition and destruction.
Role of merkel cells
Merkel cells are found deep within the epidermis and provide contact with Merkel discs.
These discs are the flattened ends of sensory neurones and they are responsible for sensing touch upon the skin.
Layers of the epidermis
- Stratum basale
- Stratum spinosum
- Stratum granulosum
- Strata lucidum
- Stratum corneum
- Stratum basale
This is a single row of cuboidal or columnar keratinocytes. Some are stem cells undergoing mitosis and hence dividing to produce new keratinocytes. Melanocytes and Merkel cells are scattered amongst this layer. The skin cannot regenerate if a significant part of this layer is destroyed – If this occurs the patient will need skin grafts.
- Stratum spinosum
This consists of 8-10 layers of keratinocytes fitted close together. It is a very strong layer and also contains Langerhans cells.
- Stratum granulosum
This consists of 3-5 layers of flattened keratinocytes which are undergoing apoptosis. There are also lamellar granules containing and secreting a lipid secretion (waterproofing). This secretion fills the spaces between cells. This layer is the transition layer between deep, living
tissue and dead upper layer.
- Strata lucidum
This layer is only present in the thicker skin of the fingertips, palms and soles. It is made up of 3-5 layers of flattened clear keratinocytes. There is a large amount of keratin present.
- Stratum corneum
This layer consists of 25-30 layers of dead keratinocytes which are continuously being shed and replaced. The keratinocytes are now mainly keratin. The lipid secretion from the lamella cells forms a water repellent barrier. A callus, formed through constant friction, is an abnormal thickening of this layer.
Keratinization
New keratinocytes are pushed up from the stratum basale. These cells accumulate keratin as they move up through the epidermis. When they reach the stratum granulosum, they undergo apoptosis, after which they are pushed to the surface of the skin and sloughed off.
This movement of approximately 0.1 mm of skin takes about 35 days in total. When the skin is damaged the rate of cell division in the stratum basale (i.e. the production of new keratinocytes) increases to help with the repair of the wound
The dermis
The dermis is a connective tissue layer containing collagen and elastic fibres. It has great tensile strength and contains very few cells and is divided into two regions: the papillary and the reticular. The cells that are present are mainly fibroblasts, but there are also macrophages and adipocytes present. The dermal layer contains the blood vessels, nerves, glands that supply the skin and hair follicles.
Papillary region of the dermis
The papillary region constitutes approximately 20% of the dermis and is made up of thin collagen and fine elastic fibres. The surfaces of the dermal papillae project up into the underside of the epidermis. These papillae contain capillary loops, tactile receptors (Meissner corpuscles) and free nerve endings for warmth, coolness, pain, tickling and
itching.
Reticular region of the dermis
The remainder of the dermis is the reticular region. This consists of dense, irregular connective tissue containing fibroblasts, collagen bundles and coarse elastic fibres. It is
attached to the subcutaneous tissue. The collagen fibres are arranged in a net-like structure and between the collagen fibres are adipose cells, hair follicles, nerve cells, sebaceous glands and sweat glands.
The colour of a person’s skin is formed from:
- Melanin – this varies the skin colour from pale yellow to reddish-brown (these differences are most obvious in hair)
- Haemoglobin – this gives pink tones to the skin (when a patient is hypoxic they become cyanosed and their skin takes on a blue colour)
- Carotene – this is the precursor of vitamin A. If there is an excessive intake this is stored in the stratum corneum and the dermis
2 forms of melanin
There are two forms of melanin: pheomelanin (yellow-red) and eumelanin (brown-black).
Every person has roughly the same number of melanocytes and skin colour differences are due to amount of melanin produced and transferred to keratinocytes. Accumulations of melanin take several forms: freckles, age spots, nevae (moles). Melanin synthesis is stimulated by UV light which leads to a suntan.
Dark skin contains
Dark skin contains a large amount of melanin in the epidermis.
Light skin contains
Light skin contains little melanin in the epidermis and so the skin is translucent and the colour is given by the oxygen content of the blood below the surface.
Accessory Structures – Hair
Hair is present on most skin surfaces and is made up of columns of dead keratinized keratinocytes held together by extracellular proteins. The hair shaft protrudes above the surface of the skin whilst the root is either within the dermis or the subcutaneous layer.
Hair and surrounding structures
The hair follicle surrounds the root whilst the bulb houses the papilla. The papilla contains connective tissue and blood vessels and the hair matrix the latter being the germinal cells responsible for hair growth and regeneration. The arrector pili muscle is the smooth muscle responsible for raising the hair vertically. The hair root plexuses which surround the follicle
respond to touch on the skin.
Accessory Structures – Sebaceous Glands
These are absent from the palms of the hands and the soles of the feet. Sebaceous glands secrete sebum, a mixture of triglycerides, cholesterol, proteins and inorganic salts. Sebum coats the surface of the hairs to prevent drying and brittleness. Sebum also has a role in reducing water loss from the skin and inhibition of some bacteria.
Accessory Structures – Sweat (Sudoriferous) Glands
Eccrine Glands
- These are the most numerous of the sweat glands and are found extensively on the forehead, the palms and the soles of the feet. The secretory portion is located deep in the dermis and the sweat is secreted through the pores on the skin. Their main function is to regulate body temperature and in doing so sweat is formed first on the forehead, moving through the rest of the body before lastly forming on the hands and feet. However, these glands may also be stimulated by emotional stress resulting in “cold sweats”.
Apocrine Glands
- These are found mainly in the axillae, groin, aureolae and the beard area. Their secretions are more viscous than that of eccrine glands and the secretory portion of the gland is found in the subcutaneous layer opening out onto the hair follicle. The secretion is milky and/or yellowish in colour and its components are metabolised by bacteria on the skin resulting in a characteristic body odour. The apocrine glands do not begin to function until puberty. They are stimulated by emotions and by sexual activity.
Accessory Structures – Nails
Nails are plates of hard, dead, tightly packed keratinized epithelial cells.
The nail body is pink due to the capillary blood supply whilst the free edge is white because there is no underlying blood supply. The hyponychium (the nail bed) is a layer of thickened stratum corneum. The nail root is embedded in the nail matrix where mitotic cells produce nail growth (approximately 1mm per week, slightly less in toenails).
Skin Lesions – Terms
- Macule – flat spot up to 1cm in diameter
- Papule – raised spot up to 1cm in diameter
- Nodule – a solid lesion
- Plaque – a raised flat topped lesion
- Vesicle – a blister up to 1cm in diameter containing clear fluid
- Bulla – a blister greater than 1cm in diameter
- Pustule – a pus-containing blister
- Crust – dried plasma proteins with or without blood and inflammatory cells
- Scale – dry flaky or powdery surface
- Purpura – small haemorrhage under the skin or mucous membrane
Dermatitis
Dermatitis is characterised by acute inflammatory lesions with either the epidermis or dermis involved, often both. Characteristic patterns of the lesions generally allow
identification of the cause. Non-specific dermatitis is known as eczema.
Acute (eczematous) dermatitis
The skin is reddened, itchy and tender. Vesicles form in the epidermis and when these burst clear, yellow fluid is released followed by the formation of a crust. The itchiness may result in repeated trauma from scratching which in turn causes secondary changes to the skin resulting in chronic dermatitis.
Atopic dermatitis
This usually begins in infancy and may persist into adulthood. The flexures are most commonly affected and the dermatitis is Type I IgE mediated. There is usually a family history of atopy (including asthma, hayfever and urticaria).
Gravitational dermatitis
This affects the ankles and lower legs of patients with varicose veins (it is also known as “varicose eczema”). The chronic skin changes are due to inadequate venous drainage.
Irritant contact dermatitis
This occurs following contact with strong agents such as detergents, acids and alkalis. It most commonly affects the hands and is most often due to occupational exposure. It is important to remember that this is not an allergic reaction.
Allergic contact dermatitis
This may have an inherited component and is a Type IV mediated reaction mediated by Langerhans cells. The most common skin allergens are: nickel, rubber, dyes and materials used in cosmetics. The causative allergen is usually identified by contact testing by a dermatology clinic
Seborrheic dermatitis
This is characterised by white or waxy scale. In infants it is largely confined to the scalp and is commonly known as “cradle-cap”. The most common presentation in adults is as dandruff. It is nothing to do with the sebaceous glands!
Lichen planus
This is a common specific dermatitis. It is often diagnosed by the four Ps: • Pruritic • Purple • Polygonal • Papules
It affects the flexor aspects of the forearms, wrists, hands and ankles. It may also affect the trunk and mucous membranes. The dermatitis may persist for years and leaves a patch of pigmented skin when it is resolved.
Psoriasis
This is a chronic inflammatory dermatitis with a genetic component. It affects the skin of the: • Elbows • Knees • Scalp • Lumbosacral area • Intergluteal cleft • Glans penis Psoriasis is characterised by pink or salmon coloured plaques, often oval in shape, with definite borders. The plaques are covered in a thick white scale. The lesions contain oedematous dermal papillae and if the plaque is lifted pin-prick bleeding results. In 30% of patients there is involvement of the nails also. Psoriasis follows a relapsing/ remitting course where skin turnover is decreased from 35 days to 3-5 days.
Pityriasis rosea
This presents as red patches with a scaly rim. The primary lesion (the “herald patch”) is quite large, often 2-10 cm in diameter. The secondary lesions are smaller. The scale begins in the centre of the lesion then moves outwards. The cause is unknown but is thought to be viral in origin. It is more common in children and young adults.
Urticaria
Also known as hives or nettle rash this consists of acute, intensely itchy lesions which develop in a matter of minutes. The intense itch comes from degranulation of mast cell releasing inflammatory mediators including histamine. This causes the dermal capillaries to become leaky forming erythmatous vesicles.
Acne vulgaris
Acne is a common problem in the teenage population and can be extremely distressing for the patient. It should, therefore, not be treated lightly.
It is thought that acne vulgaris is the result of hyperactivity of sebaceous glands which in turn leads to overproduction of sebum. This then blocks the follicular openings which can result in the formation of blackheads (open comedones), whiteheads (closed comedones),
inflammatory papules, nodules and in severe cases cysts. Added to this, the normal skin flora (particularly Propionibacterium acnes) trapped within the follicles can produce proinflammatory mediators which may make the clinical appearance of the lesions worse.
Severe acne can lead to scarring, both physical and psychological. In patients with darker skins the scarring may be keloidal in nature.
Preparations for treating skin pathologies
- Acute Dermatitis (including atopic eczema, irritant contact dermatitis,
allergic contact dermatitis)
First line therapies
• Antihistamines
• Emollients (leave-on and soap substitutes)
• Topical corticosteroids
Topical corticosteroids
Topical corticosteroids can be very useful in flare-ups of eczema and dermatitis.
Hydrocortisone 1% and Clobetasone 0.05% are both available as P medicines for the treatment of mild to moderate episodes of dermatitis with restrictions as to how much and where they can be used. The max length of treatment with non-prescription corticosteroid products is seven days and they should not be used on the face. If longer courses of treatment are required then the patient should see their GP
Psoriasis treatment
There are three main categories of
treatments: topical, UV light and systemic.
Topical treatments include vitamin D analogues (e.g. Calcipotriol), corticosteroids, retinoids (e.g. Tazarotene), Dithranol and coal tar. All of these have been shown to slow down skin cell production and all except Dithranol will reduce inflammation. These drugs can be applied as creams, ointments, gels, lotions or shampoos and again, patient preference often dictates which product is prescribed.
UV light therapy usually involves exposure to short wave UV light (UVB). However in more severe cases of psoriasis the patient may be given topical or oral psoralen and exposure to longer wave UV light (UVA) – a therapy known as PUVA. There is an increased risk of skin
damage and skin cancer associated with this therapy.
Systemic treatments include methotrexate, ciclosporin, anti-TNFs (e.g. etanercept) and monoclonal antibodies (e.g. infliximab, efalizumab).
Urticaria treatment
Oral antihistamines are very effective for the intense itching of urticaria. This is a selflimiting condition and so should not need further treatment.
Acne treatment
In mild acne vulgaris topical preparations available over the counter can be of some use.
These keratolytic agents are designed to prevent the blockage of follicles (which facilitates the flow of sebum) and they may also have some antibacterial activity. These preparations include Benzoyl Peroxide, Salicyclic Acid, Sulphur and Resorcinol although the latter two are
rarely used. Both Benzyol Peroxide and Salicylic Acid are irritant to the skin and should be used at the lowest available concentrations in the first instance. If these are tolerated, then the concentration can be increased. Patients should be counselled that it may take up to 3
months for the benefits to be seen and so perseverance with therapy is important.
If these products fail to achieve a desirable result, other topical agents are available on prescription. These include Tetracycline, Clindamycin, Tretinoin and Adapalene.
If treatment with first line agents is not successful, second line therapy can be added. This usually consists of low dose oral antibiotics: Oxytetracycline, Tetracycline, Doxycycline, and Lymecycline. Minocycline is as effective as these but carries a greater risk of lupus erythmatosus-like syndrome.
In female patients where acne is thought to be hormonally linked, Co-Cyprindiol (Cyproterone Acetate + Ethinylestrodiol) may be of value.
If second line agents are ineffective then specialist referral is needed and may result in the prescription of oral Isotretinoin.
