2 - 17 - CUTANEOUS PHOTOBIOLOGY Flashcards
shortest wavelength of solar electromagnetic radiation reaching the earth’s surface
290 nm
carries sufficient photon-energy to completely remove an electron from an atom or molecule (= ionization)
Ionizing electromagnetic radiation, like, for example, x-rays or gamma rays
able to move an electron to a higher energy state, but, in contrast to ionizing radiation, cannot remove an electron from atoms or molecules
Nonionizing radiation, which includes ultraviolet radiation (UVR), visible light, and infrared radiation
Ultraviolet B wavelength
290 nm-315 nm
UVA wavelength
315 nm-400 nm
UVA1: 340 nm-400 nm
UVA2: 315 nm-340 nm
Visible light wavelength
400 nm-760 nm
a photoproduct of photoexcited 7-dehydrocholesterol
previtamin D3
photoproduct of excited DNA
cyclobutane pyrimidine dimer
process in which energy from an excited chromophore is transferred to another molecules
photosensitized reaction
Upon photoexcitation, a photochemical reaction can occur to form a new, different molecule
photoproduct
Identify if UVA or UVB:
Immediate erythema
UVA
Identify if UVA or UVB:
Delayed melanogenesis (peaks at 3 days)
UVB
Identify if UVA or UVB:
Immediate pigment darkening (within 20 minutes after UVR exposure)
UVA
Identify if UVA or UVB:
Major role in drug induced photosensitivity; contributes to carcinogenesis
UVA
Identify if UVA or UVB:
associated with sunburn
UVB
1000 × more erythemogenic than UVA
Identify if UVA or UVB:
Central role in photoaging
UVA
UVB also has a role in photoaging
Identify if UVA or UVB:
Major role in carcinogenesis
UVB
Identify if UVA or UVB:
Penetrates down to deep dermis
UVA
Identify if UVA or UVB:
Not associated with vitamin D production
UVA
Identify if UVA or UVB:
Penetrates no deeper than the upper dermis
UVB
Identify if UVA or UVB:
Role in vitamin D production
UVB
Identify if UVA or UVB:
Penetrates window glass
UVB
Identify if UVA or UVB:
Immunosuppression
BOTH
sunburn typically peaks how many hours after sun exposure?
6 to 24 hours
tanning peaks approximately how many days after UVB exposure?
3 days
chromophore for UVR-induced tanning, very similar to erythema formation
DNA
Identify the skin phenotype
- Always burns, never tans
- Pale white
I
This is the lowest dose that causes erythema in an individual
minimal erythema dose
Identify the skin phenotype
- Rarely burns, tans easily
- Brown; moderately pigmented
V
Identify the skin phenotype
- Sometimes burns, can tan without prior burn
- White
III
Identify the skin phenotype
- Burns only with very high UVR doses, tans
- Dark brown to black; darkly pigmented
VI
Identify the skin phenotype
- Usually does not burn, tans easily and deeply
- White to light brown
IV
Identify the skin phenotype
- Always burns, then tans
- White
II
Photo-phytodermatitis is a phototoxic reaction mediated by plant-based chromophores, namely what?
furocoumarins
Berloque dermatitis is also a phototoxic dermatitis, in which the chromophore is what perfume ingredient?
bergamot oil (5-methoxy psoralen)
the chromophore that mediates the antipsoriasis therapeutic efficacy
DNA
absorption maximum of DNA
260 nm
UV signature mutations
C → T and the C:C → T:T tandem mutations at dipyrimidine sites
most of the oxidative DNA damage after exposure to natural sunlight is caused by which UVR
UVA
The only nonproliferative feature of photoaged skin that is not observed in intrinsically aged skin
Actinic elastosis
The only positive effect of UVR on skin
vitamin D production
