physiology of the skin Flashcards
functions of the epidermis
- Waterproofing
- Physical barrier
- Immune function
- Vitamin D synthesis
- UV protection
- Thermoregulation
functions of the dermis
- Thermoregulation
- Vitamin D synthesis
- Sensory organ
functions of the subcutis
- Thermoregulation
- Energy reserve
- Vitamin D storage
- Endocrine organ
- Shock absorber
what causes the skin to be a waterproof barrier
tight junctions in stratum granulosum
epidermal lipids and keratin in stratum corneum
why does skin wrinkle when wet?
- Mediated by sympathetic nervous system
- Due to vasoconstriction in dermis
- Improves grip
how does the skin act as a physical barrier
- Structure of skin helps resist trauma
- Stratified epithelium helps resist abrasive forces
- Fat in subcutis acts as shock absorber
how does the skin synthesise vit D
• 7-dyhydrocholesterol in plasma membranes of epidermal keratinocytes and dermal fibroblasts converted to previtamin D3 by UVB
how does the skin store vit D
• Lipid soluble – can be stored in subcutis adipocytes
name 2 hormones which site of action is in the skin
- Androgens act of follicles and sebaceous glands
* Thyroid hormones act on keratinocytes, follicles, dermal fibroblasts, sebaceous glands, eccrine glands
name 3 hormones which have their site of synthesis in the skin
vit D3
5 alpha-reductase -> 5alpha-dihydrotestosterone
insulin-like growth factor
how does UV-a and UV-b damage skin
- Burns
- Suppress action of Langerhans cells
- Photo-aging
- DNA damage (skin cancers)
what 3 things does skin colour depend upon
- Melanin
- Carotenoids
- Oxy/deoxyhaemoglobin
how is melanin synthesised and transported
- Synthesised in melanosomes within melanocytes from tyrosine
- Transported via dendrites to adjacent keratinocytes
what are the 2 types of melanin
- Pheomelanin (red/yellow)
* Eumelanin (brown/black)
what type of melanin do all skin types contain more of?
eumelanin
what is the role of melanin
- Photoprotective – scatters/filters UV light
- Prone to photodegradation
- Lots of melanin = less able to utilize UV light to make vitamin D
how does our skin respond to sunlight
- Immediate pigment darkening - photooxidation 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
how is the skin a barrier to infection?
• A range of peptides synthesised by granular layer keratinocytes have antimicrobial properties
what immune cells are present in the epidermis
Langerhans cells
what immune cells are present in the dermis
o Regulatory T cells o Natural killer cells o Dendritic cells o Macrophages o Mast cells
what happens when the immune organ of the skin is challenged
- LC migrate to dermis and lymph nodes and activate a T-cell response
- Keratinocytes proliferate & secrete cytokines
- Leucocytes enter skin from blood
how is the skin a sensory organ
• Merkle cells - basal epidermis (Light touch)
• Encapsulated mechanoreceptors in dermis
o Pacinian corpuscles (Pressure/Vibration)
o Meissner corpuscles (Touch)
• Myelinated and unmyelinated sensory nerve endings in dermis (Pain, Itch, Temperature)
what insulates to maintain body temp
subcutaneous fat
how is heat lost from the skin?
• Cutaneous blood flow
o Deep vascular plexus (lower reticular dermis)
o Superficial vascular plexus (upper reticular dermis)
o Loops of blood vessels from superficial plexus extend to reticular dermis
• Eccrine sweating
why are humans endothermic homeotherms
heat is generated through metabolism
what does evaporation depend upon
- Surface area exposed to environment
- Temp and relative humidity of ambient air
- Convective air currents
heat storage equation
Heat storage = metabolism – work – evaporation +/- evaporation =/- conduction +/- convection
describe the autonomic regulation of blood flow in dermal vascular plexuses
• Sympathetic alpha-noradrenergic: vasoconstriction
• Sympathetic cholinergic: vasodilation
• (Both in hairy skin. Hairless skin only has cholinergic innervation)
Sympathetic cholinergic nerves that govern sweating may be the same as those controlling active vasodilation
Nitric oxide may play a role in active vasodilation
how does piloerection arise
- Arrector pili muscles innervated by sympathetic α1-adrenergic fibres
- Contraction raises cutaneous hairs
- Likely little significant impact on heat conservation
what acts as an energy store in the skin
subcutaneous fat
white adipose connective tissue
