Photobiology Flashcards
What is the wavelength of UVR?
100-400nm; 5% of solar radiation
Wavelengths less than what wavelength do not penetrate the earth’s atmosphere and what are these called?
290nm do not penetrate because of the ozone, called UVC and it can be lethal if it does
What light is between 290-320nm? What filters them out? What is this spectrum referred to as?
UVB; window glass filters out; sunburn spectrum; SPF testing based on this
What spectrum is UVA? Does it penetrate glass? How deep does it penetrate? What is it responsible for?
320-400nm; least potent and does penetrate glass but it does penetrate deeper than UVB so it is responsible for photo aging.
List some modifications in UVR on Earth.
Elevation, atmosphere, latitude, reflection, clouds, solar flare, season, time of day
How much does the ozone block?
Almost all <300nm
What is the percentage of light that is UVA that reaches the earth’s surface?
95-98% which means the remaining percent is UVB and UVC blocked completely
How much % increase is seen in UVR with each 1000 feet increase in altitude?
4%
How much do most surfaces reflect?
<5% UVR
How much does water reflect?
7%
How much does sand reflect?
25%
How much does fresh snow reflect?
80%
What does cloud cover do to UVR?
Scatters but doesnt absorb
What happens when sunlight hits the skin?
Some reflected, some absorbed in epidermis and dermis by DNA, some penetrates deeper
What is the reaction to a given wavelength called?
Action spectrum
How is action spectrum determined?
Properties of molecule that initiates the response: chromophore
What is the major UVB chromophore in the skin?
DNA (urocanic acid, armoatic amino acid)
What is responsible for the majority of the effects of UVR on skin?
UVB
What do acute and chronic responses to UVR depend on?
Skin type
What do skin types I-VI vary in?
Susceptibility to burning, ability to tan, and risk of skin cancer (pretty much goes from ginger/albino to black/brown skin)
What are some of the acute effects of UVR on skin?
Inflammation(sunburn), immunomodulation, tanning, epidermal hyperplasia, Vitamin D synthesis, DNA damage (apoptosis or repair)
What is sunburn mostly due to?
UVB
What is erythema from sunburn the result of?
Vasodilation
What is heat of a sunburn the result of?
Increased blood flow
What is swelling of sunburn due to?
Vasopermeability
What is pain/pruritis of a sunburn due to?
Release of cytokines
When does hyperkeratosis and acanthosis happen in a cell that has been sunburned?
72 hours after sunburn
What are the two types of suntans?
Immediate and delayed
What is the immediate tan response caused by?
UVA and visible light, fades within an hour, due to oxidation and redistribution of existing melanin
What is the delayed response tan caused by?
UVB and it is gradual (visible in 72 hours and lasts for weeks); caused by increased melanin synthesis and increased transfer of melanosomes to keratinocytes and can provide some photoprotection
What is a chronic effect of UVR on skin?
Photoaging and Photocarcinogenesis (BCC and SCC and melanoma)
Compare and contrast chronologic vs photoaging.
Chronologic is smooth, pale finely wrinkled skin with benign growths compared to dry, deeply wrinkled, inelastic, leathery, and atrophic in photoaging. Photo also has telangiectasis, irregular pigmentation, comedone and cyst formation, malignancies (pretty much your skin looks like shit)
Although UVB is 20-50x more efficient at photoaging, why is UVA more responsible for it?
It is present at much greater concentrations and is capable of deeper penetration = more dermal damage
What is the majority of direct DNA damage due to?
UVB; damage occurs from direct absorption of photons by bases of DNA
What are the DNA photoproducts? The two examples given are?
They are dimers formed by covalent binding of two adjacent pyrimidines in the same polynucleotide chain; Cyclobutane and 6,4 photoproducts
What happens if UV induced DNA damage is not efficiently repaired?*
UV signature mutations (C->T) and (CC->TT); remember these are INTRAstrand
How does stratum corneum protect against UVR?
Reflection
How does melanin protect against UVR?
Absorption
What TSGs are associated with protection against UVR?
p53, patched, CDKN2A (p16)
What is xeroderma pigmentosum (XP)?
Heritable dz characterized by marked sensitivity to UV radiation; deficient repair of UV induced DNA damage (usually defect in nucleotide excision); high rates of skin cancer at very young age; increased risk of malignancies
When does XP manifest?
Early childhood with marked sensitivity
What is evidence of photo damage indicating XP?
Early appearance of freckles, early wrinkling, and skin atrophy
What is the median onset for first skin cancer in XP?
8 years
For XP patients under 20… what are their risks of nonmelanoma cancer and melanoma?
10000x greater and 2000x greater
What else can XP effect?
Eyes (premature aging, dry eyes, corneal scarring, cataracts); CNS (Neuro degen)
When will most XP patients die by?
32, from metastatic skin cancer and neurologic degeneration
How is immunosuppression caused by UV light?
Lymphocytes and Langerhans cells are sensitive to UV light; Langerhans cells disappear from the skin following exposure strong enough to cause a mild sunburn
Does UVR cause local and systemic effects?
Yes
What are some dz’s treated by sunlight?
Psoriasis, Cutaneous Lymphoma, and Eczema
How does sunlight treat dz?
Some skin dz that cause enhanced lymphocytes and/or langerhans cells can be treated with UV light
What light does tanning bed emit?
Primarily UVA (most with some UVB); >5x normal UVA per unit time than solar UVA
True or False. UVA tans are better than UVB tans when it comes to providing protection against sunburn.
False, UVA induced tans provide 10x less protection than UVB and are strongly associated with melanoma and nonmelanoma skin cancer
How much of an increase in the risk of cancer is seen in individuals who start using tanning beds before 30?
75%; increased incidence primarily seen in young women
T/F. Tanning beds are a classified as a carcinogen.
True
