W8 - Effect of environment on skin Flashcards
What is the integument?
Interface between body and environment. Thus
subject to a wide range of insults (stresses).
Why is skin a vital organ?
On extensive epidermal (or epidermal + dermal) damage, e.g. with severe burns
or a rare drug reaction, death may occur, owing to one or more of:
* Dehydration and shock
* Infection
* Heat loss and hypothermia (or sometimes hyperthermia due to impaired
thermoregulation).
* Others: protein loss, electrolyte imbalance, high-output cardiac failure, renal
failure.
What is Toxic epidermal necrolysis?
(rare adverse drug reaction)
Detachment of epidermis. Often fatal.
What is an environmental ‘insults’?
- Irradiation & UV light
- Physical trauma (burns, friction, pressure
etc) - Allergens
- Irritant
- Microbes
These upset the homeostasis, thermoregulation etc…
What are the Protective features of the skin?
- Drying: Waterproof epidermis + oil from sebaceous glands
- Friction, impact:
- Thick, regenerating epidermis; keratin
- Nails
- Basement membrane anchoring epidermis to dermis, wavy border against shear forces
- Collagen fibres in dermis (strong, running in all directions)
- Heat: Sweating; vasodilatation
- Cold: Subcutaneous fat, adaptable blood supply, hair (head)
- Burns, injury: Thick, regenerating epidermis
- Radiation/sunlight: thick epidermis; melanin
- Infections: Impervious epidermis; resident cells of immune system
What are the Normal skin adaptations to environmental pressures?
- Sweating & vasodilatation in heat;
vasoconstriction in cold. Quite fast
(minutes). - Hyperkeratosis (callus): thickening of
stratum corneum with rubbing or pressure
(e.g. feet, guitarist fingers), or (slightly) after
ultraviolet exposure. Slow (weeks). - Tanning: (melanocyte response) after
ultraviolet exposure. Quite slow (days).
How does thermoregulation by blood supply help?
Arteriovenous (AV) shunts are anastomoses
between arterioles and venules. Numerous in
dermis.
Respond to thermoreceptors in skin – hot/cold.
Shunts open or close respectively to decrease or
increase blood flow to the superficial vascular
plexus in the papillary dermis (just below epidermis).
Hence skin goes redder (more heat loss) or bluer.
In face: can also respond to emotion/ sympathetic nervous system – blushing.
Shut off for too long – danger of damage (frostbite).
How does UV protection through epidermal melanin work?
- The colour of human skin is due mainly to melanin (dark skin) and haemoglobin (light skin)
- Much normal genetic variation in the amount of melanin (>12 genes known)
- Melanin protects against DNA damage and thus
skin cancer, especially in dark (black & Asiatic)
skin: incidence only 8-10% that of white people
Transfer of melanosomes (pigment granules) mainly to basal keratinocytes
How is tanning a form of protection?
Melanocytes increase activity - make &
transmit more melanin.
Gives some protection against UV.
Additional protection by skin thickening in
response to UV.
MSH: melanocyte-stimulating hormone
MC1R: melanocortin 1 receptor
What is UV protection? Basics of suntanning?
MSH - melanocyte-stimulating hormone
MCIR - melanocartin I receptor
From UVR damage, there would be DNA damage signalling the release of MSH from the basal keratinocyte to the MCIR receptor in the melanocyte. This result in the transcriptional increase of melanin synthesis and transfer and increase in cell division.
The thing being transcribed in Tyrosinase (TYR).
Tyrosine-related proteins (TRPs)
Tyrosine - (TYP) -> L-DOPA - (TYR) -> DOPAquinone - (TRPs)–> Eumelanins( Brown/black) or Pheomelanins (Yellow to Red)
How does skin protect against microorganisms?
Langerhans cells (& rest of immune system)
Small cells in non-basal layers of skin.
Dendritic cells.
Function: Antigen-presenting cells (like
macrophages). Form a network in the
epidermis – part of immune system.
What are examples of environmental insults?
Friction/ scratching
Ultraviolet irradiation
Burns
Irritants
Allergens
Microbes (bacteria, viruses, fungi)
What is Lichenification?
More extreme form of hyperkeratosis.
Reaction to excessive rubbing or scratching/skin conditions. Leathery/tree bark appearance from addition to wrinkles etc.
This is a reaction to friction/scratching
How does sunburning work?
Solar UV Radiation in relation to the Earth and ozone layer.
* Is a radiation burn
* Blisters, inflammation and cell death
(severe DNA damage)
* “Ever sunburnt” associates with
increased risk of skin cancer
* So does “ever used a UV sunbed
below age 35” – by 75%
When we are out in the sun, we are exposed to both UVA and UVB. UVB is most associated to skin cancer - suncream.
What is Polymorphic light eruption?
Manifestation in the form of a rash - several types of sun allergies.
