Devo Lect 12 - Epidermis Flashcards
Epidermis and dermis from
From ectoderm and mesoderm respectively
Malpighian cells
aka basal cells; stem cells in bottom of epidermis; 2 weeks to reach cornified layer then 2 weeks before shed
Where does differentiation occurs in epidermis?
In the granular layer, keratin produced
Keratin
Structural protein, released from keratin granules
Transitional cells
After granular layer, protein synthesis decreasing, cells flattening out and dying
Cornified layer
Dead cells on the outer surface, Loaded with keratin. Key for protection.
Melanocyte
Pigment cell, in the epidermal layer but not from the ectoderm, it’s from the neural crest cells, produces melanosomes
Growth factors involved in development of epidermis
TGFa: autocrine from basal cells, regulates their division; KGF: keratinocyte growth factor, paracrine, from dermal fibroblasts, regulates basal cell proliferation
Psoriasis
Over-expression of TGFa; get thickened cornified layer, produced faster (like 2 days instead of 2 weeks)
Psoriasis mouse
Transgenic test, gain of function, increased TGF-a expression
Cutaneous appendages
hair, scales, feathers; interaction of ecto- and mesoderm; all made similarly
Hair production
Interaction between ectoderm and mesoderm, change initiated. Ectoderm starts to protrude down, produces condensed mesoderm which becomes dermal papilla (base of shaft); ectoderm cells pack together, lots of keratin, die off, then get pushed outward; hair stem cells (bulb), sebaceous gland
Trichology
Study of hair
Lanugo hair
Hairs developing in the fetus, shed just before birth, then normal hair development starts after birth
Glabrous skin
skin that doesn’t have hair (ie palms)
Vellus and terminal hairs
Fine hairs (like fingers) vs large hairs (head); affected by combination of growth factors
Chemotherapy and hair
Chemo stops fast growing cells, hairs are some of the fastest in the body.
Baldness
it’s a conversion from terminal hair to vellus hair, a reverse of youth (vellus to terminal ie beard); caused by dihydroxy testosterone (DHT), the hormone is changed as you age.
Finasteride
drug that reverses baldness, it’s a steroid (potential side affects?); it’s a competitive inhibitor of the enzyme that converts testosterone to DHT, helps convert hairs back; originally made to help lower elevated testosterone from prostate cancer
Congenital universal hypertrichosis
Ambras syndrome; aka werewolf syndrome, terminal hairs all over, esp on face
Hirsutism
hypertrichosis in women, like bearded lady; caused by abnormal androgen secretions
