S3: The Effect of Enviroment on the Skin Flashcards
List factors that can cause extensive epidermal/dermal damage to skin
- Dehydration and shock
- Infection
- Heat loss and hypothermia/hyperthermia
- Protein loss, electrolyte imbalance, high output cardiac failure/renal failure
What is toxic epidermis necrolysis?
It is an example of severe epidermal damage due to an adverse drug reaction. There is detachment of the epidermis which is often fatal.
Why is the skin so vital?
The skin protects from a wide range of enviromental insults.
This includes: Irradiation + UV light, physical trauma (burns, friction, pressure etc), irritants, allergens and microbes or ectoparasites.
How are the negative impacts of the enviroment on the skin limited?
They are limited due to adaptations of the skin which can be fast or slow.
Give an example of fast adaptations of the skin against enviromental effects
Sweating and vasodilation in heat or vasoconstriction if it’s cold
Give examples of slow adaptations of the skin against enviromental effects
Hyperkeratosis which is a thickening of the stratum corneum with rubbing or pressure e.g. feet.
Another long term adaptation is through the presence of melanocytes where we tan after UV exposure.
Describe how melanin protects against UV damage normally
Melanin is made by melanocytes, the cells are often low in the basal epidermal layer or just below. With dendrites that “feed” melanin to keratinocytes.
There is transfer of melanosomes (pigment granules) to basal cells.
- The melanin within the basal keratinocytes are often arranged so they sit on top of the nucleus to protect the DNA.
What is the colour of human skin due to?
The colour of human skin is due to melanin (dark skin) and haemoglobin (for light skin).
How do we tan?
A person tans when melanocytes increase their activity by making and transmitting more melanin. The signal to produce more melanin is via DNA damage within the melanocyte by UV. This gives some protection against UV.
Additional protection is provided by skin thickening in response to UV.
What is lichenification?
It is a more extreme form of hyperkeratosis and often the skins reaction to excessive rubbing or scratching. It can also be caused by various skin conditions.
Describe the three types of UV
- UVC is blocked by the ozone layer
- UVB and UVA can penetrate the atmosphere and damage skin. UVA is the longest of UV wavelength and it is the most penertrating.
List and explain some effects of UV radiation on the skin
- Sunburn which is a radiation burn. It is often seen as blisters, inflammation and cell death (with severe DNA damage). A sunburn increases risk of skin cancer.
- Polymorphic light eruption is a sun allergy
- Wrinkles/solar elastosis
- Naevi (moles) which are benign proliferation of melanocytes.
- Freckles/ephelides
- Solar lentigos/liver spots/age spots often appear at the back of hands
- Solar keratosis are abnormal growths of keratinocytes, common on bald peoples head.
What are the categories of skin cancer?
Skin cancer can be split into melanoma (melnocytes) and non melanoma (keratinocytes).
Non melanoma can be further split into squamous cell carcinoma and basal cell carcinoma.
- Melanoma can be thin but they are dangerous due to their rapid spread.
What are the positive uses of UV?
- It is needed for vitamin D production in the skin
- UV radiotherapy for skin conditions such as vitiligo, psoriasis.
What are the different types of burns?
- Partial thickness include superficial burns which is where the epidermis has been destroyed. It also includes slightly deeper burns affecting top of dermis, just before appendages like sebaceous glands.
- Full thickness burns will scar, these are very deep and loses both the epidermis and dermis. There is loss of pinprick sensation when the patient presents acutely.
Describe irritant contact dermatitis
This occurs when there is too much exposure to a substance e.g. irritants such as washing powder, soap. The substance can still be used but the amount needs to be reduced. People often vary in their sensitivity. Symptoms include redness, itching, swelling, blistering and scaling.
Describe allergic contact dermatitis
This is an allergy to something that contacts the skin and the immune system is involved. Only a tiny amount of allergen can be involved or a lot and the time taken for allergy to develop varies. Allergens include metals, leather, latex etc. Allergens should be avoided in the future.
Which is more common: irritant contact dermatitis or allergic contact dermatitis?
Irritant contact dermatitis is more common.
Explain the mechanism of allergic contact dermatitis
In allergic contact dermatitis there are stages:
- First there is sensitization, this is where Langerhans cells process the antigen and present it to the lymphocytes.
- There is then something called delayed hypersensitivity, which is in essence where the lymphocytes go away and “think about it” and on the next exposure decide to mount a response (memory T cells).
Give examples of fungi, bacterial and virus ‘insults’ to the skin
- Paronychia is a nail fold infection that can be fungal or bacterial
- An example of a fungal infection is tinea capitis (scalp ringworm)
- A bacterial example is impetigo and cellulitis e.g. Streptococcus invading blood vessels. This can lead to bacteraemia which is an systemic infection.
A viral example is HPV, causing warts
How do microbes affect the skin?
Microbes can gain their portal of entry via breach in the epidermis (e.g. streptococcus in cellulitis).
Also impaired immunity predisposes a person to infection, for example HIV and viral warts. There can also be situations such as herpes virus infecting eczema (eczema herpeticum).
