5-5 sunlight effect on integument

Interaction Between Sunlight and Vitamin D Production

  • Learning Outcome: Describe the interaction between sunlight and vitamin D3 production.

  • Significance of Sunlight Exposure:

    • Limited sunlight exposure can be beneficial for health.
    • Excessive sunlight can cause damage to epidermal and deeper tissues.

  • Mechanism of Vitamin D3 Production:

    • Epidermal Cells:
    • When exposed to UV radiation, epidermal cells in the stratum spinosum and stratum basale convert a cholesterol-related steroid into cholecalciferol (vitamin D3).
    • Chemical name for cholecalciferol: 7-dehydrocholesterol.
    • Conversion Process:
    • Once synthesized, cholecalciferol is sent to the liver.
    • The liver converts cholecalciferol into an intermediary compound.
    • This intermediary is used by the kidneys to synthesize the hormone calcitriol (1,25-dihydroxyvitamin D).
    • Function of Calcitriol:
    • Calcitriol is crucial for the absorption of calcium and phosphate ions in the small intestine.
    • An inadequate supply leads to impaired bone maintenance and growth.

  • Sources of Vitamin D3:

    • Natural Sources:
    • Two primary sources of cholecalciferol (Vitamin D3):
      1. Sunlight: Skin synthesis via UV radiation.
      2. Diet: Absorbed through the digestive tract from foods like:
      • Egg yolks
      • Fish oil
      • Fortified milk
    • Definition of Vitamin:
    • The term vitamin refers to essential organic nutrients needed from the diet due to insufficient body production.
    • Cholecalciferol is categorized as a vitamin when dietary intake is required for normal bone development.

  • Clinical Note on Skin Cancer:

    • Most common form of cancer involves skin cancers.
    • Benign Tumors:
    • Examples include moles and warts; generally noncancerous.
    • Skin Cancers:
    • Two main types:
      1. Basal Cell Carcinoma:
      • Originates in the stratum basale; most common skin cancer.
      • About two-thirds occur in chronic UV-exposed areas.
      1. Squamous Cell Carcinoma:
      • Less common, restricted mainly to sun-exposed skin areas.
      • Rarely leads to metastasis if treated.
      • Typical treatment involves surgical removal.
      • Five-Year Survival Rate: Approximately 95% post-treatment.
      1. Malignant Melanomas:
      • Extremely dangerous as they grow rapidly.
      • Possibility of metastasizing through the lymphatic system or blood vessels.
      • Survival Rate: 99% if detected early; drops to 14% if diagnosed after extensive metastasis.

  • Early Detection of Melanomas:

    • Mnemonic ABCD helps to remember key characteristics:
    • A: Asymmetry (one half unlike the other)
    • B: Border (irregular borders)
    • C: Color (multiple colors such as tan, brown, black, red, pink, white, blue)
    • D: Diameter (greater than 6 mm, about the size of a pencil eraser)
    • E: Evolving (changes in size, shape, or color may indicate melanoma)

  • Sun Protection Recommendations:

    • Avoid sun exposure during peak hours (midday).
    • Use broad-spectrum sunscreen with at least SPF 15 for all skin types, as everyone can develop skin cancer.
    • Sunscreens contain organic molecules to absorb UV radiation and inorganic pigments to reflect UV rays.
    • Higher SPF correlates with increased chemical concentration in products.
    • Additional protective measures include:
    • Wearing hats with brims
    • Long-sleeved shirts and long pants

  • Environmental Considerations:

    • Ozone depletion due to industrial emissions limits UV protection provided by natural ozone.

  • Consequences of Vitamin D3 Deficiency:

    • Inability to produce sufficient cholecalciferol leads to inadequate bone maintenance.
    • Lack of sunlight exposure can cause bone development abnormalities in children, specifically rickets:
    • Rickets is characterized by fragile bones and is often associated with limited dietary cholecalciferol.
    • Prevention: Mandatory fortification of dairy with cholecalciferol in the U.S.

  • Checkpoint Questions:

    • Question: Explain the relationship between sunlight exposure and vitamin D3 synthesis.
    • Answer: UV radiation from sunlight allows epidermal cells to convert cholesterol-related steroids into cholecalciferol (vitamin D3).
    • Question: Explain potential bone problems for women who cover their skin entirely in cultures.
    • Answer: Complete body coverage inhibits UV penetration to the stratum basale, hindering vitamin D3 production, leading to fragile bones.

  • Composition of Hair:

    • Hair is primarily comprised of keratinized dead cells that are pushed to the skin surface, providing protection.