Skin Flashcards
What are the layers of the skin?
- Epidermis
- Dermis
- Subcutis
Which layers of the skin are waterproof?
Epidermis
Why does the skin wrinkle when wet?
- mediated by sympathetic nervous system
- due to vasoconstriction in dermis
Explain the function of the skin as a physical barrier
- structure of skin: resists trauma
- stratified epithelium: resists abrasive forces
- fat in subcutis: shock absorber
Explain vitamin D synthesis in the skin
7-dehydrocholestrol in plasma membranes of epidermal keratinocytes and dermal fibroblasts converted to previtamin D3 by UVB
Where is vitamin D stored in the skin?
Subcutis adipocytes
Which hormones act on the skin?
Androgens
Thyroid hormones
Where do androgens act in the skin?
Follicles
Sebaceous glands
Where do the thyroid hormones act on the skin?
- Keratinocytes
- Follicles
- Dermal fibroblasts
- Sebaceous glands
- Eccrine glands
What does skin colour depend on?
- Melanin
- Carotenoids
- Oxy/deoxyhaemoglobin
Describe melanin secretion
Synthesised in melanosomes within melanocytes from tyrosine
Transported via dendrites to adjacent keratinocytes
What are the functions of melanin?
- skin colour
- scatters/filters UV light
What colours are:
- Phenomelanin
- Eumelanin
- red/yellow
- brown/black
Does everyone have the same number of melanocytes?
Yes
Density varies between body cites
Does the skin contain more eumelanin or pheomelanin?
Eumelanin
Deleterious effects of melanin
- Prone to photodegradation (may generate ROS)
- Pheomelanin increases release of histamine
- Lots of melanin = less ale to utilise UV light to make vitamin D
Skin response to sunlight
- Immediate pigment darkening
- Persistent pigment darkening
- Delayed tanning
Explain immediate pigment darkening
- photooxidation of existing melanin
- redistribution of melanosomes
- occurs within mins and lasts hours-days
Explain persistent pigment darkening
(Tanning)
- UVA»_space; UVB
- oxidation of melanin
- occurs within hours
- lasts 3-5 days
Explain delayed tanning
- increased melanin synthesis
- occurs 2-3 days after UV exposure
- maximal at 10-28 days
Explain the skin’s barrier to infection
The properties that render the skin a barrier to water also help prevent infection
A range of peptides synthesised by granular-layer keratinocytes have antimicrobial properties
Which cells in the epidermis contribute to the immune system?
- Langerhans cells
- keratinocytes
How do Langerhans cells contribute to the immune system
- antigen-presenting cells
- secrete cytokines
How to keratinocytes contribute to the immune system?
Secrete cytokines and chemokines
Which cells in the dermis contribute to the immune system?
- Regulatory T cells
- Natural killer cells
- Dendritic cells
- Macrophages
- Mast cells
What is the skin’s immune response?
- Langerhans cells migrate to dermis -> lymph nodes activate a T-cell response
- Keratinocytes proliferate and secrete cytokines
- Leucocytes enter skin from blood
What are the sensory cells in the skin?
- Merkle cells
- Pacinian corpuscles
- Meissner corpuscles
- Myelinated & unmyelinated sensory nerve endings
Where are the sensory cells in the skin found?
Dermis
Except Merkle cells - found in basal epidermis
What do Merkle cells sense?
Light touch
What do Pacinian corpuscles sense?
Pressure / vibration
What do Meissner corpuscles sense?
Touch
What do myelinated and unmyelinated sensory nerve endings in the skin sense?
- pain
- itch
- temperature
What is the insulating factor in the skin?
subcutaneous fat
What prevents heat loss in the skin?
- Cutaneous blood flow
- Eccrine sweating
- Hair
What is the equation for heat storage?
Heat storage = metabolism - work - evaporation +/- radiation +/- conduction +/- convection
Describe autonomic regulation of the skin
Sympathetic alpha-noradrenergic: vasoconstriction
Sympathetic cholinergic: vasodilation
Explain the mechanism of piloerection (goosebumps)
- Arrector pili muscles innervated by sympathetic alpha-adrenergic fibres
- Contraction raises cutaneous hairs
What does subcutaneous fat in the skin act as?
- insulator
- shock absorber
- energy store
