Skin: Effect of Environment Flashcards
What is integument?
Interface between body and environment - Thus subject to a wide range of insults (stresses)
Explain the significance of skin as a vital organ
On extensive epidermal (or epidermal + dermal) damage, e.g. with severe burns or a rare drug reaction, death may occur
What may occur to cause severe skin damage resulting in death?
- Dehydration and shock
- Infection
- Heat loss and hypothermia (or hyperthermia due to
impaired thermoregulation)
Others: protein loss; electrolyte imbalance; high-output cardiac failure; renal failure
What is toxic epidermal necrolysis?
(rare adverse drug reaction)
Detachment of epidermis. Often fatal
Give examples of environmental insult to skin
- Irradiation and UV light
- Physical trauma (burns, friction, pressure)
- Irritants
- Allergens
- Microbes, ectoparasites etc.
How does the skins ability to dry aid protection?
Drying: Waterproof epidermis + oil from sebaceous glands
What factors aid skins ability to protect against friction and impact?
Thick, regenerating epidermis; keratin
Nails
Basement membrane anchoring epidermis to dermis, wavy border against shear forces
Collagen fibres in dermis (strong, running in all directions)
How does thermoregulation of skin maintain homeostasis?
Heat: Sweating; vasodilatation
Cold: Subcutaneous fat, adaptable blood supply, hair (head)
How is the skin adapted to deal with burns?
Thick, regenerating epidermis
How does skin react to sunlight and radiation?
thick epidermis; melanin
How does skin fight infection?
Impervious epidermis; resident cells of immune system
Outline a fast response from the skin?
Sweating & vasodilatation in heat; vasoconstriction in cold. Quite fast (minutes)
What are the slower ways skin adapts to the environment?
Hyperkeratosis: thickening of stratum corneum with rubbing or pressure (e.g. feet, guitarist fingers), or (slightly) after ultraviolet exposure. Slow (weeks)
Melanocytes: tanning after ultraviolet exposure. Quite slow (days).
What are arteriovenous shunts?
Arteriovenous (AV) shunts found across the dermis, are anastomoses between arterioles and venules
What is the role of AV shunts?
Respond to thermoreceptors in skin – hot/cold
Explain why the skin turns red/blue in extreme temperatures?
Av shunts open and close to increase/decrease blood flow to superficial vascular plexus in the papillary dermis (just below epidermis)
Hence skin goes redder (more heat loss) or bluer
What other factors contribute to redness/bluish colour of skin?
In face: can also respond to emotion/ sympathetic nervous system – blushing.
Shut off for too long – danger of damage (frostbite)
What 2 molecules mainly contribute to the colour of skin?
The colour of human skin is due mainly to melanin (dark skin) and haemoglobin (light skin)
What is the normal range of melanin in the body?
Much normal genetic variation in the amount of melanin (>12 genes known)
Apart from pigmentation what is the role of melanin?
Melanin protects against DNA damage and thus skin cancer, especially in dark (black & Asiatic) skin: incidence only 8-10% that of white people
How does melanin contribute to skin colour?
Melanocytes transfer melanosomes (pigment granules) mainly to the basal keratinocytes
What effect does tanning have on the skin?
Melanocytes increase activity - make & transmit more melanin.
Gives some protection against UV.
Additional protection by skin thickening in response to UV.
Outline the protective mechanism of skin against suntanning
Basal level of melanin constantly present in keratinocyte
- UVR causes DNA damage in the keratinocyte
- The DNA damage creates signalling molecules resulting
in MSH production - MSH binds to its MC1R receptor stimulating melanocyte
activity - Causes stimulation of MSH and melanocyte production => produces more melanin
At what level is suntanning safe?
Sun tanning is never safe - any sun tan causes DNA damage
