Effect of the Environment on Skin Flashcards
what are three normal skin adaptations to environmental pressures?
sweating and vasodilation against heat, vasoconstriction against the cold
hyperkeratosis - thickening of the stratum corneum against constant rubbing/pressure at an area
tanning against UV rays - slow response form melanocytes after UV exposure, gives a tanned/pigmented appearance
list the potential types of environmental “insults” upon the skin.
- severe burns and rare drug reactions causing extensive/severe damage
- toxic epidermal necrolysis from a rare adverse drug reaction = epidermis detaches
- irradiation and UV light = causes damage to skin cells, leading to skin cancers and premature ageing
- physical trauma = causes tissue damage, scarring, may impair function
- irritants, allergens, chemical agents = skin irritation, inflammation, triggering allergic reactions of varying severities
- microbes or parasites = infections, infestations, skin damage
list protective features of the skin
waterproof epidermis and oil form sebaceous glands for drying
thick regenerating epidermis, wavy border anchoring the epidermis against shear forces, collagen dermal fibres providing tensile strength = protect against friction/impact
sweating and vasodilation against heat; subcutaneous fat in hypodermis and vasoconstriction against the cold
thick epidermis and melanin form melanocytes protects from UV damage
impervious epidermis, resident Langerhans cells protect against infections
what are the subpapillary plexus and the cutaneous plexus? how are they supplied?
subpapillary plexus - network of blood vessels close to the skin surface, under dermal papillae
cutaneous plexus - network of blood vessels at the dermal-hypodermal border
supplied by the subcutaneous arteries and veins
what are AV shunts?
arteriovenous shunts - anastomoses between arterioles and venules that allow blood to be shunted directly across
respond to thermoreceptors in the skin
describe thermoregulation when the environment is too HOT, involving skin plexus and AV shunts
increase in temperature is detected by thermoreceptors - blood needs to be supplied to the skin surface for skin to be lost
AV shunts are closed allowing continuous blood supply through subcutaneous arteries to the subpapillary plexus - heat is lost at the skin surface - deoxy. blood taken away by veins
the skin gets redder due to increased blood supply to the skin surface
describe thermoregulation when the environment is too COLD, involving skin plexus and AV shunts
decrease in temperature is detected by thermoreceptors - need to reduce blood supply to the skin to minimise heat loss
AV shunts open = blood is shunted directly from arterioles to venules, doesn’t reach the subpapillary plexus
skin gets bluer as blood is shunted away and doesn’t reach the skin surface
what is the danger of cutting off blood supply to the subpapillary plexus for too long?
blood supply to the subpapillary plexus is cut off as a thermoregulatory measure against the cold
for too long - can cause damage to the epidermal skin layers and risk frostbite
cells within the epidermal skin layers need blood supply to function, proliferate and differentiate
how does the skin adapt to protect against UV rays?
increases melanocyte activity to make and transmit more melanin from melanocytes to basal keratinocytes
more melanin = more protection against UV rays, DNA damage and skin cancer
summarise melanin production
melanin is produced in the epidermal layer by melanocytes
transmitted via melanosome granules through melanocytes dendrites to basal keratinocytes
describe the cellular mechanism of tanning in response to UV radiation
UV radiation causes DNA damage in basal keratinocytes
triggers DNA damage signalling = MSH is released from basal keratinocytes
MSH binds to MC1R receptors on melanocytes - triggers downstream signalling events involving cAMP
results in increased transcription of tyrosinase - this enzyme synthesises melanin
results in increased rate of production of melanin, but the same constitutive amount is produced in granules - also causes some skin thickening
how does melanin production differ between hair and nails?
initially melanin production is the same - tyrosine is hydroxylated to L-DOPA, which is oxidised to DOPA-quinone ; both processes catalysed by tyrosinase
in skin = eumelanin is produced
in hair = pheomelanin
what are Langerhans cells? how are they involved in protection of the skin?
Langerhans cells = small, dendritic antigen-presenting cells on the non-basal layer of the skin
work with the rest of the immune system and form a network in the epidermis as antigen-presenting cells
what is hyperkeratosis?
skin thickening in a particular area - result of excessive pressure, inflammation or irritation to the skin
what is Lichenification?
more extreme form of hyperkeratosis form excessive rubbing/scratching
gives skin an exaggerated wrinkled, leathery appearance
