UV radiation Flashcards by Malindi Haggett

What are the wavelengths for UVA? UVB and UVC?

UVC: 200 -290 nm
UVB: 290 - 315 nm
UVA: 315 - 400nm

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UVA1 and UVA2 wavelengths?

1: 340 - 400
2: 315 - 340

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290 - 315 wavelength?

UVB

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More than 95% of the radiation that reaches the earths surface is UVB

False - UVA

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Longer UV wavelength penetrate deeper into the skin

True

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Most of UVB is absorbed in the epidermis and little reaches the epidermis

True

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Systemic sunburn reaction is mediated by?

IL6 - absorbed into the circulation and causes malaise, somnolence, fever and chills

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What is the most important chromophore for UVB?

DNA

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What is the most important chromophore for UVA and visible light?

Porphyrin

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Define sunburn?

Solar erythema and possible blister formation followed by desquamation

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What are the short term effects of UV radiaiton?

Sunburn
Tanning

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Histological changes with sunburn?

Epidermal oedema - Spongiosis
Acanthosis
Hyperkeratoses
Apototic keratinocytes
Depletion of langerhans cells
Increased epidermal melanin
Inflammatory infiltrate of lymphocytes and neutrophils
Vasodilation

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The ability of UV to induce sunburn increases with increasing wavelengths

False - declines with increasing wavelengths

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UVB induced sunburn reaches its peak between __ and __ hours after exposure?

6 and 24 hours

(NB: immediate erythema is rare)

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UVA is more likely to cause an immediate erythema reaction compared to UVB

True

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The dose of UVA present in natural light are not sufficent to cause a sunburn reaction

True

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Describe the tanning response in humans

Biphasic
- immediate: due to UVA, pigment darkening due to redistribution of existing melanin
- delayed: due to UVB, peaks 3 days after sun exposure

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A UVB tan provides 5 - 10 times less sunprotection against subseuent UV exposure than a UVA induced tan

False - other way around

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Describe the long term effects of UV exposure, what are the mechanisms that lead to this?

Photoageing
Photocarcinogenesis

Mechanism:
- generates DNA damage, leading to mutations and malignant transformaiton
- has immunosupressent properties (increased tolerance to antigens from skin tumours)

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What is Photoaging?

Encompasses the clinical, histologic and physiologic changes present in chronically sun exposed skin

Upregulation of ECM degrading proteases and downregulation of collagen synthesis

= Loss of collagen and deposition of abnormal degenerative elastotic material

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What is the absorption maximum wavelength for DNA?

260

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How does UVA and UVB produce DNA damage?

UVB is more directly mutagenic.
UVA is more oxidative (UVA’s biological effects (e.g., toxicity) are mainly due to ROS generation (requires oxygen).

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UVC (200–290 nm) reaches the basal layer of human skin.

False

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UVB (290–315 nm) is the primary inducer of DNA photoproducts in the epidermis.

True

UVA (315–400 nm) penetrates more deeply than UVB, reaching the dermis.

True

The DNA absorption maximum is at 300 nm.

False

Cyclobutane pyrimidine dimers (CPDs) are the most common UV photoproducts.

True

6,4‑photoproducts cannot activate DNA damage response pathways.

False

“Dark CPDs” arise from continued photochemistry in melanin‑containing cells after UV exposure.

True

UVA is incapable of forming any pyrimidine dimers.

False

Oxidative DNA damage (e.g., 8‑oxoG) is primarily caused by UVB.

False

Nucleotide excision repair (NER) handles bulky UV photoproducts.

True

Global genome repair is initiated by RNA polymerase II stalling.

False

Transcription‑coupled repair relies on CSA/CSB recruitment.

True

XPF–ERCC1 makes the incision on the 3′ side of a lesion.

False

Base excision repair (BER) removes entire oligonucleotides around lesions.

False

XP patients have defects in NER and are prone to early skin cancers.

True

XP-variant is due to malfunction of DNA polymerase‑η.

True

XP-variant patients have no NER defects.

True

Pol‑η accurately bypasses T–T dimers by inserting two cytosines.

False

UV exposure upregulates p53, causing cell‑cycle arrest.

True

Translesional synthesis always prevents mutations.

False

Homologous recombination can rescue stalled forks when bypass fails.

True

UVB is the principal cause of delayed erythema (“sunburn”).

True

Immediate tanning is mainly driven by UVB.

False

Delayed tanning requires melanocyte proliferation and occurs after UVB.

True

UV irradiation increases Langerhans cell density in skin.

False

Cis‑urocanic acid formation contributes to UV‑induced immunosuppression.

True

UV exposure can induce regulatory T cells (Tregs).

True

The Th17/IL‑23 axis is upregulated by therapeutic phototherapy in psoriasis.

False

Chronic UVA exposure upregulates dermal MMPs leading to collagen breakdown.

True

UVB is the main driver of dermal elastosis in photoaging.

False

Photocarcinogenesis requires only DNA mutations, not immune changes.

False

Intermittent high‑dose UV is most strongly linked to melanoma risk.

True

SPF measures UVA protection.

False

A broad‑spectrum, photostable sunscreen provides balanced UVA/UVB defense.

True

Sunscreens should be reapplied regularly because filters can photodegrade.

True

Higher SPF always correlates with better protection against photoaging.

False

Eumelanin is a less effective radical scavenger than pheomelanin.

False

Epidermal thickening reduces basal keratinocyte UV exposure.

True

Antioxidant enzymes in skin quench reactive oxygen species.

True

Pheomelanin acts as a photoprotector under UV exposure.

False

Phototherapy induces apoptosis of pathogenic T cells in CTCL.

True

NB‑UVB and UVA1 share identical immunomodulatory profiles.

False

Phototherapy can reduce pruritus via neural mediator alteration.

True

UVA1 worsens morphea by increasing collagen deposition.

False

Phototherapy in psoriasis can lower systemic CRP levels.

True

UV exposure has no effect on lipid profiles in treated patients.

False

UV irradiation has been linked to improved motor learning and mood.

True

Topical DNA‑repair enzymes can accelerate photoproduct removal.

True

Oral nicotinamide has been shown to increase actinic keratosis rates.

False

Sunscreen use can potentially disrupt the cutaneous microbiome.

True

Repeated sub‑erythemal UV exposures can upregulate NER capacity.

True

UV exposures strengthen cutaneous immune surveillance long-term.

False

UVC from tanning beds contributes significantly to melanoma risk.

False

Melanin‑mediated dark CPDs occur hours after UV exposure.

True

Base excision repair involves glycosylases that remove entire nucleotides.

False

Fibrotic skin diseases like morphea can improve under UVA1 via MMP induction.

True

UV‑induced ROS are solely harmful and have no protective roles.

False

Sunscreens should not be used to prolong intentional sun exposure.

True

Xeroderma pigmentosum patients benefit from topical DNA‑repair enzyme application.

True

High‑dose UVA tanning in salons has not been linked to any skin cancers.

False

UV radiation Flashcards

(83 cards)