Skin: Effect of Environment on Skin Flashcards
In terms of skin, what is an insult?
Anything capable of causing physical damage, mutation, infections etc.
What can occur if the skin becomes damaged?
- Dehydration and shock - loss of homeostatic function due to skin damage so ability to regulate and serve as waterproofing function is lost
- Infection - can start at the skin and spread to the lymphatics and the rest of the body system
- Heat loss and hypothermia (or sometimes hyperthermia due to impaired thermoregulation causing uncontrollable flare ups) - due to loss of homeostasis
- Others: protein loss, electrolyte imbalance, high-output cardiac failure, renal failure.
What is toxic epidermal necrolysis?
A very serious condition which can be fatal. Often due to rare adverse drug reaction. There is detachment of epidermis.
What are some environmental insults?
- UV radiation
- Physical trauma e.g. burns, friction, pressure etc
- Irritants - e.g. chemical agents/substances
- Allergens - substances capable of triggering an allergic reaction on the immune system
- Microbes, ectoparasites etc - microbes can penetrate the skin and cause infections. Ectoparasites live on the skin and cause damage.
What are some protective features of the skin?
- Waterproof epidermis plays a huge role in protecting against dryness as well as oil from sebaceous glands
- Thick regenerating epidermis full of keratin, nails, wavy border between epidermis and dermis, collagen fibres in dermis all protect against friction and impact
- Sweating and vasodilatation protect against heat
- Adaptable blood supply, subcutaneous fat (insulation), hair helps protect against cold
- Thick regenerating epidermis protects against burns and injury
- Thick epidermis and melanin produced by the melanocytes protect against radiation/sunlight
- Impervious epidermis and Langerhans cells (resident cells of the skin that are part of the immune system) protect against infections
What are some normal skin adaptations to environmental pressures?
- Sweating and vasodilatation in response to heat and vasoconstriction in cold. Occurs in minutes.
- Hyperkeratosis (callus): thickening of stratum corneum (cornified layers) with rubbing or pressure (e.g. feet, guitarist fingers), or (slightly) after ultraviolet exposure. Takes weeks to occur.
- Tanning after UV exposure. Melanocytes respond and produce more melanin which serves as protection from UV rays. Melanin gives the pigmented appearance of the skin. Takes days to occur.
Describe the network of blood vessels in the skin.
- Plexus close to the surface is the subpapillary plexus. This is located just beneath the dermal papilla.
- Plexus in the middle is the cutaneous plexus. This is located at the border between the dermis and hypodermis.
- Plexi are made up of blood vessels - arteries, veins, capillaries, arterioles, venules.
- Plexi are supplied by subcutaneous arteries and veins. The aim of the arteries and the arterioles is to supply oxygenated blood to the skin surface (subpapillary plexus). The aims of the veins and venules is to take blood away from the surface of the skin.
- Arteriovenous (AV) shunts are anastomosed (connecting structures) between arterioles and venules that supply blood to the subpapillary plexus. Numerous in dermis.
- In a normal situation, arterioles supply blood to the subpapillary plexus, make its way to the capillaries, venules take the deoxygenated blood up from the capillaries and then takes the blood back. However with the shunts between the arterioles and the venules this can be bypassed, shunting blood directly from arterioles to venules.
- The shunts respond to thermoreceptors in skin
How does thermoregulation occur?
Shunts open or close to decrease or increase blood flow to the superficial vascular plexus (subpapillary plexus) in the papillary dermis. Hence skin goes redder (more heat loss) or bluer (blood supply to surface shut off so there is deoxygenated blood).
- When there is increased temperature, the shunt is closed which allows continuous blood supply through the arterioles to the subpapillary plexus. From there the heat can be lost through the surface of the skin.
- In response to cold, the shunts open and instead of the blood reaching the surface, it is instead shunted straight from the arterioles to the venules which take the blood back to retain body temperature.
When blood supply of the subpapillary plexus is shut off for too long, there is danger of damage to the epidermal skin layers because they need blood supply and oxygen to have continuous cell division and normal differentiation and function within the layers of the dermis (frostbite). So if it is shut off for too long you can have death and damage of the skin layers.
What happens in response to UV radiation?
- Get DNA damage in the basal keratinocyte
- Results in the synthesis and secretion of MSH (melanocyte-stimulating hormone)
- MSH leaves the keratinocyte and binds to the MC1R (melanocortin 1 receptor) on the melanocyte
- This then triggers signalling events, particularly cAMP signalling
- Results in transcription of the enzymes that go on to synthesis melanin
- Once the enzymes are synthesised they go on to make the melanin and as a result there is more melanin being produced and supplied to the basal keratinocyte.
Describe the increased transcription in response to UV radiation.
- Increased transcription of the enzyme tyrosinase
- Tyrosinase hydroxylates tyrosine (an amino acid) into L-DOPA.
- Tyrosinase also oxidises L-DOPA into DOPAquinone
- In the skin: Eumelanins are being produced (there are more of it in people with darker skin)
- In the hair: Pheomelanins are being produced. These are responsible for naturally brighter hair pigmentation
What is Lichenification?
- Occurs in response to friction/scratching e.g. tight fabric on skin
- Exaggeration of normal skin features e.g. wrinkles, scales etc.
- Leathery, tree-bark like appearance.
What are the three categories of UV radiation?
UVA - able to penetrate the atmosphere and reach the earths surface and skin.
UVB - able to penetrate the atmosphere and reach the earths surface and skin. Most implicated with skin cancer.
UVC - most dangerous and has shortest wavelength.. Filtered out by atmosphere due to the ozone layer.
What is polymorphic light eruption?
- Reaction to UV radiation
- Manifests in the form of a rash.
Describe skin cancer categories.
- Skin cancer broadly divided into melanoma skin cancer (affects the melanocytes) and non-melanoma skin cancer (affects mostly the keratinocytes in the skin).
- Melanoma skin cancer is the more dangerous skin cancer whereas the non melanoma skin cancer is more common.
- The non-melanoma cancer is further subdivided into squamous cell carcinoma (skin cancers that affect the upper layers of the skin) and basal cell carcinoma
(affect cells in the basal layer of the epidermis) - The basal cell carcinoma is the commonest from of non-melanoma skin cancer.
What are some positive aspects of UV?
- UV needed for vitamin D3 production in skin
- UV radiotherapy for skin conditions can be e.g. vitiligo, psoriasis
