Lecture 23B - Skin Damage Flashcards
Damage to the skin?
adverse drug reactions
allergic reactions, contact with chemicals
wounds and wound healing
sunburn and melanoma
disturbance of the microbiota and infection
What are the 4 stages of wound healing?
hemostasis
inflammation
proliferation
remodelling
What can penetrate the external layer of the skin?
cuts, penetration of thorns or other sharps and injuries can penetrate through the skin layers right down to vital organs below
Wha does haemostasis involve?
stopping the bleeding by clot formation
What is released in haemostasis?
histamine from mast cells which causes vasoconstriction as well as changing permeability of the blood vessel wall
What do neutrophils and macrophages do in haemostasis?
enter the damaged area to help remove damaged cells and any bacteria/pathogens which have been introduced beneath the surface barrier of the skin
What is the clot?
a temporary plug which fills the breach in the skin until it can be repaired
What happens in inflammation?
in response to chemotactic factors, monocytes will migrate to the damaged tissue by diapedesis and differentiate into macrophages
What do factors released from macrophages and neutrophils do?
cause more cells to be recruited to the site of injury and for specific aspects of immune system to be activated
What does inflammatory factors and cytokines do?
cause the site to become hot and throbbing
What is proliferation?
alongside the inflammatory response, cell proliferation responses begin to repair the damage
What does a scab (eschar) do?
helps protect the underlying repair processes
What do endothelial cells do?
proliferate as they repair blood vessels
What do fibroblasts do?
help repair the connective tissue matrix as well as repairing the skin layer at the top itself
What does closure of a cut involve?
myofibroblasts
What do myofibroblasts do?
sit at the edge of an open cut and extend a podium forward as they migrate across the open space in the wound and form a continuous barrier
What do their myofibrils do?
contract to pull the normal cells at the edge of the cut along behind them
What does the action of fibroblasts do?
helps pull the two separate edges of the cut together till the epidermal layer becomes continuous again
How long does complete remodelling take?
a few months for it to be as strong as it was before injury
continues for a long time after the surface has been resealed by the skin
What are factors that can directly affect wound healing?
body site
infection
vascular supply
mechanical stress
desiccation
edema
Factors which can indirectly affect wound healing?
age and nutrition, medication, alcoholism, drug abuse, hygiene
diabetes
autoimmune disease
venous stasis
predisposition to keloids
some genetic skin diseases
immunocompromised state
obesity, immobility, vaculitis, neuropathy
What can compromise healing in some tissues?
medical conditions such as cardiovascular disease
What does elasticity of skin change with?
age
What does tanning involve?
p53 activation in keratinocytes in response to UVR-induced DNA damage
What does p53 activation lead to?
p53 up-mediated regulation of proopiomelanocortin (POMC)
What does posttranslational cleavage of POMC produce?
beta endorphin and alpha-MSH
What does alpha-MSH do?
stimulates MC1R on adjacent melanocytes, resulting in melanin synthesis and eventual transfer of melanin-containing vesicles to keratinocytes (pigments) which causes a tan
What are melanosomes?
melanin containing vesicles
What does chronic UVR result in?
elevated circulating beta endorphin levels, leading to analgesia and a physical dependence on tanning
What is MSH?
melanocyte stimulating hormone
What ca overexposure to UV radiation induce?
skin cancer
tanning does not eliminate the potential damage from overexposure to UV
What are darker skin tones?
protective as skin cancer is much less common among African-Americans
What are lighter skin tones better for?
vitamin D production, but more susceptible to DNA damage by strong sunlight
What is non-melanoma cancer?
most commonly diagnosed cancer in Scotland
it is readily treatable if detected early
What does squamous cell carcinoma?
arises fro mature keratinocytes and can appear as recurrent open sore (bleeds)
What is basal cel carcinoma?
arises in the germinal layer of keratinocytes and invades the tissue
Where does melanoma occur?
in the melanocytes and is a more serious form of cancer which needs to be detected as early as possible to maximise the chance of successful treatment
Types of non-melanoma skin cancer?
squamous cell carcinoma and basal cell carcinoma
How many bacteria are there on our skin?
1 million bacteria per cm2
What is the microbiota?
the microbial biocommunity of bacteria, viruses and fungi
What do the bacteria on skin do?
protect the skin from colonisation of harmful bacteria and microbes - a sterile skin provides opportunities for pathogens to invade
What is healthy skin home to?
trillions of bacteria, viruses and fungi
What does genetic predisposition mean?
can make is easier for microbes to breach the skin barrier or make the skin more sensitive to their presence
some peoples sin can be thinner and the protective barrier is weaker
How can metabolic diseases affect the skin?
can alter the balance of nutrients on the skin and the vascular supply to the skin, leading to an increase in the density of microbes or a change in the relative proportions of their individual populations
What can happen if the skin is breached by a wound?
members of the microbiota which are normally harmless on the skin surface could act as pathogens once they get access to the internal tissue
What can happen once an infection of the skin takes route?
additional skin microbes may contribute to inflammatory processes which can themselves cause tissue damage
How can treatments affect the skin?
e.g. topical steroids
or environmental changes can change growth conditions for microbes and facilitate overgrowth of potentially harmful bacteria
