Effects of the Environment on the Skin (skin)

Question 1

Outline

Answer 1

• the skin is a vital organ
• normal adaptations of the skin to environmental pressures
• abnormal effects to environment:
• physical damage to skin, nails and hair
• UV damage to burns, ageing and skin lesions including cancer
• irritants, allergies and dermatitis
• cutaneous infections

Question 2

The integument

Answer 2

• interface between body and environment

- subject to a wide range of insults/stresses

Question 3

Damage to skin

Answer 3

On extensive epidermal and dermal damage, eg severe burns or a rare drug reaction, death may occur, owing to one or more of:

• dehydration and shock
• infection
• heat loss and hypothermia (sometimes hyperthermia due to impaired thermoregulation)
• others: protein loss, electrolyte imbalance, high-output cardiac failure, renal failure
• toxic epidermal necrolysis: rare adverse drug reaction causing detachment of epidermis, can often be fatal

Question 4

Environmental insults/stresses

Answer 4

These insults can cause damage to the body organs such as epidermis, dermis and fat swell as body process such as homeostasis and thermoregulation:

• irradiation and UV light
• physical trauma (burns, friction, pressure etc)
• irritants
• allergens
• microbes and parasites etc

Question 5

Protective features of the skin

Answer 5

Drying: 
- waterproof epidermis and 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 
- vasodilation
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

Question 6

Normal skin adaptions to environmental pressures

Answer 6

• sweating and vasodilation in heat and vasoconstriction in cold
• quite fast (minutes)
• hyperkeratosis (callus): thickening of stratum corneum with rubbing or pressure (eg feet, guitarist fingers), or slightly after UV exposure
• slow (weeks)
• tanning: melanocyte response after UV exposure
• quite slow (days)

Question 7

Thermoregulation by blood supply

Answer 7

• Arteriovenous (AV) shunts are anastomoses between arterioles and venules
• numerous in dermis
• respond to thermoreceptors in skin (hot/cold)
• shunts are open or close respectively to decrease or increase blood flow to the superficial vascular plexus in the papillary dermis
• 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 eg frostbite

Question 8

UV protection: epidermal melanin

Answer 8

• the colour of human skin is due mainly to melanin (dark skin) and haemoglobin (light skin)
• much normal genetic variation in the amount of melanin (>12 genes known)
• melanin protects against DNA damage and thus skin cancer especially in dark (black and asiatic) skin: incidence only 8-10% that of white people
• transfer of melanosomes (pigment granules) mainly to basal keratinocytes

Question 9

UV protection: tanning

Answer 9

• melanocytes increase activity (make and transmit more melanin)
• gives some protection against UV
• additi0nal protection by skin thickening in response to UV

Question 10

Protection against microorganisms

Answer 10

• Langerhans and rest of immune system
• small cells in non-basal layers of skin (dendritic cells)
• function: antigen-presenting cells (like macrophages) form a network in epidermis - part of immune system

Question 11

Abnormal effects of the environment (damage of insults)

Answer 11

• friction/scratching
• UV irradiation
• burns
• irritants
• allergens
• microbes (bacteria, viruses, fungi)

Question 12

Lichenification

Answer 12

• friction/scratching
• more extreme form of hyperkeratosis
• reaction to excessive rubbing or scratching/skin conditions

Question 13

Solar UV radiation in relation to Earth and ozone layer

Answer 13

• UV irradation
• Sun releases UVA, UVB, UVC wavelengths of radiation
• Ozone blocks UVC and a bit of UVA and UVB but both reach earth

Question 14

Sunburn

Answer 14

• 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%)

Question 15

Naevi (moles)

Answer 15

• singular (naevus)
• benign proliferation of melanocytes
• many or large naevi: risk factor for melanoma skin cancer

Question 16

Freckles (ephelides)

Answer 16

• involve a genetic component
• linked to red/fair hair
• often MC1R gene variants
• sun-exposed areas

Question 17

Skin cancer

Answer 17

• Melanoma (melanocytes and keratinocytes) most dangerous and common
• squamous cell carcinoma
• basal cell carcinoma

Question 18

Other diseases

Answer 18

• polymorphic light eruption
• wrinkles (solar elastosis, loss of elasticity)
• solar lentigos (liver, age spots), age related
• solar keratoses (dysplastic growth of keratinocytes)
• basal cell carcinoma (rodent ulcer), often curable by surgery
• melanoma, can be thin but still dangerous as spreads rapidly
• burns

Question 19

Good side of UV

Answer 19

• UV needed for vit D3 production in skin
• 15 min summer sun on face and arms per day enough for white skin, longer for dark skin (or take tablets)
• UV radiotherapy for skin conditions eg vitiligo, psoriasis

Question 20

Irritant contact dermatitis

Answer 20

• occurs when too much exposure to a substance
• can still use it but reduce amount
• people vary in sensitivity
• any of: redness, itching, swelling, blistering and/or scaling

Question 21

Allergen contact dermatitis

Answer 21

• allergy to something that contacts skin (immune system involved)
• tiny amount may be sufficient
• varies greatly between people
• may develop after long or short use
• any of: redness, itching, swelling, blistering and/or weeping
• avoid allergen in future

Question 22

Allergens and Irritants

Answer 22

• irritant contact dermatitis is common
• allergic contact dermatitis is relatively uncommon (eg nickel)
• sensitisation first: langerhans cells process antigen and present to lymphocytes
• delayed hypersensitivity occurs at next exposure (memory T cells)

Question 23

Microbes (fungi, viruses, bacteria)

Answer 23

• Paronychia (nail fold infection - fungal or bacterial)
• Tinea capitis (scalp ringworm - fungal)
• Impetigo (bacterial)
• Cellulitis (streptococcus - bacterial)
• Human papilloma virus HPV (warts - viral)

Question 24

Infection

Answer 24

• portal of entry: microbes can enter breach in epidermis (eg Streptococcus in cellulitis)
• impaired immunity predisposes to infection:
• eg HIV and viral warts
• eczema herpeticum which is herpes (cold sore) virus infecting eczema

Question 25

Summary

Answer 25

• the skin is a vital organ with normal adaptive mechanisms to: temperature changes (sweating, vasodilation and vasoconstriction), friction (hyperkeratosis) and UV radiation (melanin production)
• exposure to environmental ‘insults’ can cause damage to skin
• these include: friction/scratching, UV radiation, burns, irritants, allergens and microbes