Effect of the environment on the skin Flashcards
Define integument
The interface between body and environment. Thus subject to a wide range of insults (stresses).
On extensive damage to the epidermis e.g with a severe burn, death may occur and lead to problems such as:
- Dehydration and shock
- Infection
- Heat loss and hypothermia (or sometimes 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)
A detachment of epidermis. Often fatal
Give some examples of environmental factors that affect the skin (5)
- Irritation
- Physical trauma (burns, friction and pressure)
- Allergens
- Irritants
- Microbes, ectroparasites
What are the protective features of the skin?
How is the skin resistant to drying, friction, heat, cold, burns, radiation and infection
Drying: Waterproof epidermis + oil from sebaceous glands
Friction, 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)
Heat: Sweating; vasodilatation
Cold: Subcutaneous fat, adaptable blood supply, hair (head)
Burns, injury: Thick, regenerating epidermis
Radiation/sunlight: thick epidermis; melanin
Infections: Impervious epidermis; resident cells of immune system
What are the normal skin adaptations to environmental prsssures?
- Sweating & vasodilatation in heat; vasoconstriction in cold. Quite fast (minutes).
- Hyperkeratosis (callus): thickening of stratum corneum with rubbing or pressure (e.g. feet, guitarist fingers), or (slightly) after ultraviolet exposure. Slow (weeks).
- Tanning: (melanocyte response) after ultraviolet exposure. Quite slow (days).
What are Arteriovenous (AV) shunts and where are they found?
Arteriovenous (AV) shunts are anastomoses between arterioles and venules. Numerous in dermis.
What do AVs respond to?
Respond to thermoreceptors in skin – hot/cold.
Shunts open or close respectively to decrease or increase blood flow to the superficial vascular plexus in the papillary dermis (just below epidermis). Hence skin goes redder (more heat loss) or bluer.
In face: can also respond to emotion/ sympathetic nervous system – blushing.
Shut off for too long – danger of damage (frostbite).
What happens to the skin when we get to hot/cold?
- ↑Temp = Homeostatic response is more blood flow to the skin surface with the aim of heat loss via skin surface
- ↓ Temp =Homeostatic response is reduced blood flow to the skin surface with the aim of retaining as much core heat and preventing any further heat loss.
How does tanning protect against UV radiation?
- Melanocytes increase activity - make & transmit more melanin.
- Gives some protection against UV.
- Additional protection by skin thickening in response to UV.
Describe the mechanism for tanning
On image
What is Lichenification caused by scratching?
• More extreme form of hyperkeratosis. Reaction to excessive rubbing or scratching/skin conditions
Leathry, tree bark appearance
What is sunburn?
What does it cause?
- Is a radiation burn
- Blisters, inflammation and cell death (severe DNA damage)
- “Ever sunburnt” associates with increased risk of skin cancer
- So does “ever used a UV sunbed below age 35” – by 75%
Polymorphic light eruption – a type of sun allergy – a rash
What is Solar elastosis?
Wrinkles – Solar elastosis (loss of elasticity)
What is Naevi (moles) by UV?
Benign proliferation of melanocytes -> Many or large naevi: risk factor for melanoma skin cancer
