Skin Flashcards
Weight of skin
3.6kg
Surface area of skin
2m2
3 layers of skin
Epidermis
Dermis
Subcutis
Outermost layer of epidermis
stratum corneum
Epidermis is made up of
corneodesmosomes
desmosomes
Corneodesmosomes (known as…) are keep the — together
adhesion molecules
corneocytes
Increased numbers of corneodesmosomes are seen in diseases such as …
psoriasis, in which there is a thickening of the stratum corneum
Decreased number of corneodesomosomes are seen in diseases such as …
atopic eczema, where there is a thinning of the stratum corneum (= increased risk of inflammation)
Waterproof epidermis
Tight junctions between cells in the stratum granulosum,
epidermal lipids and keratin in stratum corneum form both an inside-out and outside-in barrier to water
Prevents transepidermal water loss
Epidermis
immune functions
- Keratinocytes secrete cytokines and chemokines that maintain populations of leucocytes in skin
- Langerhans cells are antigen-presenting cells and secrete cytokines
Dermis
immune
- Regulatory T cells
- Natural killer cells
- Dendritic cells
- Macrophages
- Mast cells
Vitamin D synthesis (endocrine)
- 7-dehydrocholesterol in plasma membranes of epidermal keratinocytes and dermal fibroblasts converted to previtamin D3 by UVB light
- 15-25 minutes whole body exposure produces up to 10,000 IU Vitamin D
- Serum concentrations peak 24-48 hours after exposure
- Lipid soluble - can be stored in subcutis adipocytes
UV
- Both UV-A and UV-B damage skin
- burns
- supress action of Langerhans cells
- Photo-aging
- DNA damage (skin cancers)
Skin colour depends on…
- Melanin
- Carotenoids
- Oxy/deoxyhaemoglobin
Where is melanin synthesised
Synthesised in melaonsaomes within melaoncytes from tyrosine
Melanin transport
Transported via dendrites to adjacent keratinocytes
types of melanin
- Pheomelanin (red/yellow)
- Eumelanin (brown/black)
All skin types contain more –melanin than —melanin.
All skin types contain more eumelanin than pheomelanin.
Functions of the dermis
- Thermoregulation
- Vitamin D synthesis (endocrine)
- Sensory organ
Functions of the subcutis
- Thermoregulation
- Energy reserve
- Vitamin D storage
- Endocrine organ
- Shock absorber
Subcutis as endocrine organ
→ Site of hormone action
- Androgens act on follicles and sebaceous glands - Thyroid hormones act on keratinocytes, follicles, dermal fibroblasts, sebaceous glands, eccrine glands
The skin is an ENDOCRINE ORGAN
- Vitamin D3 - unique site for cholecalciferol synthesis
- 17β-hydroxysteroid dehydrogenase in sebocytes and 5α-reductase in dermal adipocytes convert dehydroepiandrosterone (DHEA) and androstenedione to 5α-dihydrotestosterone
- Insulin-like growth factor (IGF) binding protein-3 (IGFBP-3) synthesised by dermal fibroblasts
Hypothyroidism effect on skin
- Epidermal changes
- coarsened, thin scaly skin
- Dermal changes
- Myxoedema
- Hair and nail changes
- Dry, brittle coarse hair
- Alopecia
- Thin, brittle nails
- Sweat gland changes
- Dry skin
- Decreased sweating
How do we respond to sunlight? (3)
- Immediate pigment darkening
- photo-oxidation of existing melanin
- redistribution of melanosomes
- occurs within minutes and lasts hours/days
- Persistent pigment darkening (tanning)
- UVA»_space; UVB
- Oxidation of melanin
- Occurs within hours
- Lasts 3-5 days
- Delayed tanning
- Increased melanin synthesis
- Occurs 2-3 days after UV exposure, maximal at 10-28 days