SUGER: Skin Flashcards
Why is the skin an endocrine organ?
Because it synthesises vitamin D, which is technically a steroid hormone.
Give two features which provide the waterproof function of skin.
Tight junctions between cells in stratum granulosum.
Epidermal lipids and keratin in stratum corneum.
What causes fingertips to wrinkle when wet?
Sympathetic stimulation causing vasoconstriction, which reduces the volume in the fingertips, which causes the skin to wrinkle.
Where would you find 7-dehydrocholesterol in the skin?
In cell membranes of epidermal keratinocytes and dermal fibroblasts.
What does ultraviolet B light do to 7-dehydrocholesterol?
Photochemically breaks it down into pre-vitamin D3 (cholecalciferol).
What happens to pre-vitamin D3 (cholecalciferol) after it has been made from 7-dehydrocholesterol by ultraviolet B light?
It diffuses out of keratinocytes/fibroblast cell membranes into the subcutaneous fat/subcutis, where it can be stored.
To be activated, it enters blood and travels to the liver and then the kidney.
The skin is a site of hormone action. Name two types of hormones that act on the skin.
Thyroid hormones e.g. thyroixine
Androgens e.g. testosterone
What skin changes can be detected in hypothyroidism, due to a lack of thyroid hormones acting on the skin?
Thin, coarse, scaly skin. Dry skin and less sweating.
Swelling of connective tissues of the dermis (Myxoedema).
Dry, brittle hair and nails - can cause alopecia.
A number of hormones are synthesised in the skin.
What hormone is produced when 17 beta-hydroxysteroid dehydrogenase in sebocytes and 5 alpha reductase in dermal adipocytes convert dehydroepiandrosterone and androstenedione?
5 alpha dihydrotestosterone
A number of hormones are synthesised in the skin.
What cells synthesise insulin-like growth factor binding protein-3 (IGFBP-3)?
Dermal fibroblasts.
UVA and UVB light can damage skin, for example causing burns.
How can UVA and UVB impact the immune system?
UVA and UVB suppress the action of Langerhans cells.
UVA and UVB light can damage skin, for example causing burns.
How does photo-aging damage occur?
UVA and UVB break down collagen in the dermis.
UVA and UVB light can damage skin, for example causing burns.
How does UVA/UVB exposure cause skin cancer?
UVA/UVB light can damage DNA of cells in the skin, leading to skin cancer.
What are the two types of melanin?
Pheomelanin.
Eumelanin.
Would you expect to see more pheomelanin in a person with pale or dark skin?
A person with pale skin would have more pheomelanin than a person with dark skin.
Would you expect to see more eumelanin in a person with pale or dark skin?
A person with dark skin would have more eumelanin than a person with pale skin.
Where is the most melanin in the skin, in keratinocytes or melanocytes?
Keratinocytes.
What is the more dominant melanin in all skin types, pheomelanin or eumelanin?
Eumelanin.
What is the key function of melanin?
Photoprotective function - melanin scatters/filters UV light.
Pheomelanin is prone to being broken down by sunlight. What does this photodegradation produce to trigger histamine release?
Reactive oxygen species (ROS).
What causes delayed tanning following prolonged sun exposure?
Increased melanin synthesis.
What causes immediate pigment darkening, which occurs within minutes and lasts hours-days?
Photooxidation of existing melanin and redistribution of melanosomes.
What do granular layer keratinocytes synthesise which contribute to the function of the skin as a barrier to infection?
Peptides with anti-microbial properties (e.g. LL37, beta defensins, S100A7 and S100A8).
Langerhans cells lie in between keratinocytes in the epidermis. How do Langerhans cells contribute to the immune response of the skin?
Langerhans cells phagocytose antigens then migrate through dermis to lymphatic system. Present antigens to T cells to trigger immune response.
