SKIN: Effect of Environment of Skin Flashcards
What is the importance of keratin in 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, sitting on top of the dermis, 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 top of the epidermis, 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)?
The skin is a vital organ. Due to this, on extensive epidermal (or both epidermal and dermal) damage, such as severe burns or a 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?
It is an example of severe epidermal damage; it is a rare adverse drug reaction.
It is where there is a detachment of the epidermis, which 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 (parasite that lives on the outside)
List some adaptations (fast and slow) of the skin to adapting in different environments.
We have sweating and vasodilation in heat or vasoconstriction in the cold.
In terms of slower adaptations, there is hyperkeratosis; this is the thickening of the stratum corneum with rubbing or pressure (seen in feet or guitarists fingers, or also slightly after UV exposure).
Another long-term adaptation is through the presence of melanocytes, where we tan after UV exposure.
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
Describe thermoregulation by blood supply.
Arteriovenous (AV) shunts are anastomoses between arterioles and venules. They are numerous in the dermis.
They respond to thermoreceptors in the skin - to hot and cold.
They open and close to increase or decrease blood flow to the superficial vascular plexus in the papillary dermis (just below the epidermis). Hence, the skin gets redder (more heat loss) or bluer.
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 much normal genetic variation in the amount of melanin (over 12 genes are known).
Melanin protects against DNA damage, and thus skin cancer, especially in dark (black and Asiatic skin). The incidence is only 8-10% to that of white people.
How does tanning play a role in protection?
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.
Describe how Langerhans cells protect against microorganisms.
Langerhans cells are small, dendritic cells in the non-basal layers of skin.
They function as antigen-presenting cells. They form a network in the epidermis, and are part of the immune system.
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.
It causes blisters, inflammation and cell death (due to severe DNA damage).
“Ever-sunburnt” are associates with an increased risk of skin cancer. Also, using a sunbed before the age of 35 can increase the risk by 75%.
What are naevi?
Naevi are moles. They are the benign proliferation of melanocytes.
Having many or large naevi is a risk factor for melanoma skin cancer.
What are ephelides?
Ephelides are freckles.
They involve a genetic component. It is also linked to red/fair hair. It’s often due to MC1R variants.
They can be found mostly on sun-exposed areas of the body (eg. face, shoulders, etc.).
