UVR and skin Flashcards
How UVL causes cancer; natural defense; acute/chronic effects of UVL; props of UVL
UVR wavelengths and damage
100-400nm (short) allows DNA damage
What is significant about UVC rays?
only 290nm so no atmospheric penetration but most potent of all UVL
What happens when UVC rays are produced artificially then absorbed by DNA?
RNA and proteins are damaged and may be unviable leading to lethality of epidermal cells
What waveband is SPF testing done on?
UVB (290-320nm)
Can a person inside get UVB rays?
no; glass filters it out
What is the most active in producing photochemical reactions in skin?
UVB
What is the least potent of all UVR?
UVA
What is responsible for photoaging? why?
UVA => penetrates deeper than UVB
What are factors that modify UVR at earth?
atmosphere; latitude; altitude; surface reflection; cloud; solar flare activity; time of day; season
What blocks most wavelengths below 300nm?
ozone: UVC completely blocked; UVB up to 5% remains
Why is skin cancer expected to continue to rise?
depletion of ozone layer
Why are you more likely to burn on equivalent days in Texas as compared to vermont?
sunlight travels through more atmosphere to reach surface
Who is more likely to burn on a sunny day: person in denver or in San Fransisco?
Denver as UVR is increased by 4% every 1000ft increase in altitude
Give order of most likely to burn from UVR: sand, water, snow
Snow (most likely) > Sand > water
Why can a person burn on a cloudy day?
clouds scatter the UVR but do not absorb it
What are the 3 options that sunlight has when it hits the skin?
reflect; absorbed by epidermis and dermis DNA, proteins; penetrates into tissues and dissipates
How is action spectrum determined?
UV absorbing properties of molecule that initiates the response: chromophore
What are the major UVB chromophores in skin?
DNA; urocanic acid; aromatic amino acids
Acute and chronic responses to UVR depend on what?
skin phototype (types I-VI)
What are acute effects of UVR on skin?
sunburn; immunomodulation; tan; epidermal hyperplasia; Vit D photosynthesis; DNA damage (apoptosis, cell cycle arrest)
What is the erythema and heat of a sunburn a result of?
vasodilation and increased blood flow
Why is pain/pruritus associated with sunburn?
release of cytokines
In an acute sunburn, what can be seen histologically?
keratinocyte damage; inflammation; intercellular edema; perivascular edema
72 hours after a sunburn, what can be seen?
hyperkeratosis, acanthosis
What is the pathogenesis of a suntan (immediate response)?
begins during radiation; oxidation/redistribution of melanin; no protection against UVB
What causes a suntan (immediate response)?
UVA and visible light
What causes the delayed tanning response of a suntan?
UVB
What is the pathogenesis of a delayed tanning suntan?
visible 72hrs later and lasts weeks due to increased melanin synthesis and transfer of melanosomes to keratinocytes to provide photoprotection
What are 2 chronic effects of UVR on skin?
photaging and photocarcinogenesis
What are typical cancers associated with UVR and photocarcinogenesis
BCC; squamous cell carcinoma; melanoma
What is solar elastosis?
result of chronic UV radiation seen on histological slides
clinical features of chronologic aging
smooth, pale finely wrinkled skin w/ benign growths
clinical features of photoaging
dry, deeply wrinkled, inelastic leathery, atrophic; telangiectasias; irregular pigmentation; comedone and cyst formation; actinic keratoses; benign growths
What are examples of irregular pigmentation associated with photoaging?
ephelides (freckles); solar lentigo (age spots); hypopigmentation
What are deep wrinkles on the posterior neck?
cutis rhomboidalis nuchae
What is a poikiloderma
reticulate hyperpigmentation; telangiectasia; mild atrophy
What UVRs cause photoaging?
UVB and UVA
Direct damage from UVB occurs via what mechanism?
direct absorption of photons by bases of DNA
What are DNA photoproducts?
dimers formed by covalent binding of 2 adjacent pyrimidines in same polynucleotide chain
stratum corneum defense against UVR
reflection
Melanin defense against UVR
melanin
tumor suppressor genes against UVR
p53; patched; CDKN2A
What are intracellular ways of defense against UVR?
DNA repair pathways; apoptosis
What is xeroderma pigmentosum?
heritable disease characterized by marked sensitivity to UV radiation
What are patients with XP deficient in?
deficient repair of UV induced DNA damage affecting nucleotide excision repair
What is the result of most XP patients?
high rates of skin cancers at young age with increased risk for other malignancies
What are first signs of XP?
very early photodamage=> freckles; early wrinkling; skin atrophy
When does XP typically present?
early childhood w/ marked photosensitivity
When does first skin cancer typically present in XP patients?
median age of 8
Other than skin, what other body locations are affected by XP?
CNS (neurologic degen); Eyes (premature agin, dry, corneal scarring, tumors)
What and when do most patients with XP die of?
32 y/o from metastatic skin cancer and neurologic degeneration
How does UVR cause immunosuppression?
local and systemic effects => sun exposure causes Langerhans to disappear from skin in mild sunburn due to DNA damage
When is UV light considered for Tx?
skin diseases caused or enhanced by lymphs or Langerhans => psoriasis; cutaneous lymphoma; eczema
What is significant about UVA suntans?
provide 10x less protection against sunburn than UVB
What skin diseases are strongly associated with tanning beds?
melanoma; non melanoma skin cancers
T/F Risk of skin cancer increases by 75% in ppl who use tanning beds
true
What is Favre-Racouchot syndrome?
skin disease in sun damaged individuals characterized by yellowish thickening of skin w/ nodules, comedones and follicular cysts
