Photobiology Flashcards
What percentage of solar radiation is ultraviolet?
About 5%
UV light falls into what category of wavelengths?
100-400nm (really more like 200 to 400)
Three types of UV light and their ranges?
UVC (200-290)
UVB (290-320)
UVA (320-400)
What is significant about UVC light?
At the present time, it does not penetrate the earth’s atmosphere. When it is created artificually though, it is absorbed by DNA and RNA and is lethal to viable epidermal cells
What uv light is responsible for sunburn
UVB (290-320)
Is UVB blocked out by window glass?
Yeah
What waveband is SPF testing based on?
UVB protection
What is the least potent type of Ultraviolet radiation
UVA
However, UVA penetrates glass and penetrates deeply into the skin
What is thought to be the prime cause of photoaging?
UVA light because it penetrates the skin so well.
Ozone blocks what light
Pretty much everything under 300nm
Most of the earth (95%) of what reaches earths surface is
UVA
With each increase in altitude by 1,000 feet, UV radiation goes up
by 4%
What is an action spectrum
Its a wavelength or range that elicits a certain reaction in the skin
How is action spectrum determined?
Determined by UV absorbing properties of the molecule that initiates the reaction
The molecule that initiates the reaction called
The chromophore
WHAT ARE THE MAJOR UVB Chromophores in teh skin
DNA, urocanic acid, aromatic amino acids
How many skin phototypes are there?
6…type 1= redhead, type 6= adam
Erythema in sunburn due to
Vasodilation. This also results in the skin feeling hot.
Pain and pruritis due to?
Cytokine release
What is the “immediate tanning response”
Caused by UVA light. It fades within an hour and does not protect agianst UVB. It is a result of oxidation and redistribution of melanin
What is the delayed tanning response
Caused by UVB. Becomes visible after 72 hours. Lasts weeks.
Increased Melanin synthesis and transfer of melanosomes to keratinocytes
Some photoprotection but not much
What are the major histologic changes due to chronic UV radiation
Less Collagen, damaged elastin
Chronologic aging looks like
skin will be smooth, pale, fine wrinkles and benign growths
Photoaged skin
dry, deep wrinkles, inelastic, lethery and atrophic
What is a DNA photoproduct
dimers formed by the covalent bonding of two adjacent pyrimidines in the same polynucleotide chain
Ex: cyclobutane dimers an d6,4 photoproducts.
xeroderma pigmentosum
Extreme sensitivity to UV radiation due to an inability to repair DNA damamge caused by UV light.
Usually a problem with Nucleotide excision repair
High rates of skin cancer at an early age and risk of other malignancies
Median age of first skin cancer for xp patients
Age 8
XP and the eyes
premature aging and degeneration, dry eyes, corneal scarring, cataracts, tumors
CNS and XP
Neurologic degeneration
Median age of death in xp pts
32
Because Langerhans cells disappear from the skin following sun exposure, UVB treatment can be helpful in diseases caused by lymphocytes and langerhans cells
Eczema, Psoriasis, cutaneous lymphoma
