SKIN: Effect of Environment of Skin Flashcards
What is the importance of keratin in the integument, and how is it formed?
Keratin is important in protection and adaptation.
There is a cell flow in the epidermis upwards. The basal layer, contains dividing stem cells. The daughter cells move distally through the epidermis while differentiating into mature keratinocytes, making lots of the tough and waterproof protein, keratin.
What is the significance of keratin in the stratum corneum?
the stratum corneum is made up of cornified keratinocytes that lose their nuclei and continue to move distally.
The stratum corneum is referred to as being keratinised; it is full of keratin and not much else.
At the stratum corneum, cells flake off and are constantly being replaced.
What happens when the skin is damaged (at its worst)?
On extensive epidermal damage (e.g. severe burns/rare drug reaction) death may occur.
This could be due to one or more of:
- dehydration and shock
- infection
- heat loss and hypothermia (or sometimes hyperthermia due to impaired thermoregulation)
- others (for eg. protein loss, electrolyte imbalance, high-output cardiac failure or renal failure)
What is toxic epidermal necrolysis?
an example of severe epidermal damage:
-rare adverse drug reaction where there is detachment of the epidermis and is often fatal
Why is the skin so vital?
The skin protects us from a wide range of environmental insults (stresses).
This includes:
- irradiation and UV light
- physical trauma (burns, friction, pressure, etc.)
- irritants
- allergens
- microbes
- ectoparasites (a parasite that lives on the outside)
Skin response to changes in temperature
Sweating and Vasodilatation in heat; Vasoconstriction in cold
>Quite fast (minutes)
Hyperkeratosis (callus)
thickening of stratum corneum with rubbing or pressure (e.g. feet, guitarist’s fingers), or slightly after UV exposure
>slow (weeks)
Skin response to UV exposure
Melanocytes produce melanosomes (which produce melanin), causing tanning
>quite slow (days)
List some features of the skin protecting against various stresses.
- DRYING: waterproof epidermis, oil from sebaceous glands
- FRICTION/IMPACT: thick, regenerating epidermis; 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 the immune system
What is the sub-papillary plexus?
What is the cutaneous plexus?
What lies between the sub-papillary plexus and the cutaneous plexus?
network of small blood vessels just under the papillary dermis
lower network of blood vessels at the base of the hair follicle between the reticular dermis and the hypodermis
Arteriovenous shunts in the dermis, which are anastomoses between arterioles and venules
The function of arteriovenous shunts
Thermoregulation of the blood
They respond to thermoreceptors in the skin
- AV shunt open, sub-papillary plexus gets less blood and blood flows straight from arteriole into venule and back to the heart. There is less heat loss and skin is bluer
- AV shunt closed, sub-papillary plexus gets more blood. There is more heat loss and the skin is redder.
In the face, they can also respond to emotion/the sympathetic nervous system - blushing.
If they shut off for too long, there is a danger of damage (via frostbite).
What is the function of melanin?
The colour of human skin is mainly due to melanin (dark skin) and haemoglobin (light skin). There is normal genetic variation in the amount of melanin.
transfers melanosomes (which synthesize melanin pigment) to basal keratinocytes in the epidermis
Melanin protects against DNA damage, and thus skin cancer, especially in dark (black and Asiatic skin).
How does tanning play a role in protection?
What signals for increased melanocyte activity?
Melanocytes increase their activity, making and transmitting more melanin when tanning.
This gives them some protection from UV rays.
There is also additional protection by the skin thickening in response to UV exposure.
DNA damage within the keratinocyte
STEPS of Suntanning
UVR causes DNA damage within keratinocyte signals for increased melanocyte activity:
1) Keratinocyte produces MSH
2) MSH binds receptor MC1R on melanocyte and stimulates cAMP signalling
3) Increased transcription of genes
4) Increased melanin synthesis and melanin packaged into melanosomes to be transferred to keratinocytes
5) Melanosomes build up in the keratinocyte, which causes sun tanning
Describe how Langerhans cells protect against microorganisms.
dendritic cells which form a network in upper layers of the epidermis which function as antigen-presenting cells (like macrophages)
What is lichenification?
It is a more extreme form of hyperkeratosis
It is a reaction to the excessive rubbing or scratching/skin conditions.
Describe sunburn as a result of UV exposure.
Sunburn is a radiation burn.
blisters, inflammation and cell death (severe DNA damage)
increased risk of skin cancer
What are naevi?
benign proliferation of melanocytes
many or large naevi is a risk factor for melanoma skin cancer
Skin Damage by UV: Polymorphic Light Eruption
sun allergy
Skin Damage by UV: Wrinkles (solar elastosis)
loss of elasticity
What are solar lentigos?
They are liver spots, or age spots.
They are age-related.
found in face and hands
more defined than freckles
What are solar keratoses?
They are the dysplastic growth of keratinocytes.
common on top of the head of bold people
What are the different kinds of skin cancers?
Skin cancer can be split into two types:
- Melanoma (melanocytes) - most dangerous
- Non-melanoma (mostly keratinocytes) - common
The non-melanoma cancers can be split into two kinds:
- squamous cell carcinoma
- basal cell carcinoma - commonest
Indication of basal cell carcinoma
Rodent Ulcer
*often curable by surgery, especially if reported early
What are the three types of burns?
1st DEGREE:
- a superficial burn, where only the epidermis is destroyed
2nd DEGREE:
- where the epidermis and a bit of the dermis is destroyed, just before the sebaceous glands
- it may not scar
3rd DEGREE:
- All skin layers are destroyed (down to the hypodermis)
- it will scar, and you will get a loss of pinprick sensation when the patient presents acutely
- likely to cause scarring because the dermis, which is very important for the regeneration process, is damaged
What is irritant contact dermatitis?
an inflammatory reaction of the skin caused by exposure to an irritant
can still use irritant, but reduce amount
People vary in sensitivity. Symptoms can be any of:
- redness
- itching
- swelling
- blistering/scaling
Give an example of a viral skin infection.
Human papilloma virus (HPV) [ie. warts]
- viral infection that causes warts
- those with HIV can get a worse case of HPV due to impaired immunity
Eczema
- dry flaky skin which increases vulnerability to infection and may cause eczema herpeticum, which is herpes (cold sore) virus infection eczema due to impaired immunity
