Lecture 20 - Photobiology Flashcards
1
Q
EM spectrum
A
- UVC: 200-290nm
- UVB: 290-320 nm
- UVA2: 320-340nm
- UVA1: 340-400 nm
- Visible: 400-760 nm
2
Q
Solar radiation
A
- Molecular oxygen absorbs wavelength under 200 nm
- ozone absorbs 200-330 nm
- UVB transmissin varies exponentially with ozone concentration
3
Q
Lower atmosphere abosrption
A
- role in scattering, absorption by atmospheric particles and clouds
- short wavelength more attenuated
- distance travelled alters spectrym: time of the day and altitude indue variation
- 20% more UV at altitude
4
Q
Reflectance by surface
A
- snow: 80%
- sand: 25%
5
Q
Wavelength and skin penetration
A
- the longer the wavelength, the more likely it will go through the atmosphere and through the skin
6
Q
Absorption of EM radiation
A
- chromophore: absorbs specific energy packets
- photoproducts
- photosensitisation
- emission of light or heat
7
Q
Absorption spectrum
A
- probability of absorption vs lambda
- DNA: 260 nm
- Prophyrins: 400-420
- Hemoglobin: 410
8
Q
Melanin absorption curve
A
- goot at absorbing low wavelength
- peak absorption 335
- better at absorbing UVB than UVA
9
Q
DNA damage
A
- occurs in a normal human epidermis after 1/3 of an MED
- faulty repair of photolesions -> mutations
- UVB: direct DNA damage via CPD
- UVA: indirect oxidative DNA damage via 8OxoG
10
Q
UV immunosuppression
A
- suppressive effects on cells: Langerhands cells, T lymphocytes, Mast cells, macrophages
- suppressive chemicals, cytokines, neuropeptides, interleukins
- supppressive effects on immune responses
- can ovvur with even small UV exposure
11
Q
Adverse effects of UV immunosuppression
A
- enhances carcinogenesis
- Increased sunspots
- increased skin cancers
- infections
- HSV
12
Q
What UV wavelength are harmful
A
- both UVB and UVA can cause melanoma and SCC in animals
- UVB and UVA both cause mutations in the skin
- UVB and UVA are immuno suppressive
- UVB really good at causing sunburn and carcinogenesis but very few get through the atmosphere
- UVA much more penetrant of the atmosphere but less harmful
- overall UVA more dangerous
13
Q
UV defences: Melanin
A
- abosirbs in UV, visisble
- melanosomes scatter and absorb UV
- free radical quencher
- sunburn sensitivity is determined by melanin
- susceptibility to UV immunosuppression is partly relasted to skin colour
14
Q
Skin thickening
A
- important defence for pale people
- epidermal thickening more than dermal
- increased mitosis for several days
- single UVB exposure can double skin thickness
15
Q
Good effects of UV radiation
A
- Vitamin D precursor
- deliberate UV immunosuppression to treat dermatoses
- UVB phototerapy for psoriasis, eczema, hand dermatitis, vitiligo, cutaneous T cell lymphoma
- UVA phototerapy for eczema, scleroderma, SLE
