The Skin Flashcards
What are the functions of the skin?
- synthesise Vit D
- protection from UV light
- barrier to pathogens
- thermoregulation
- control water loss
- waterproofing
What are the 3 main layers of the skin?
Epidermis
Dermis
Subcutaneous tissue (hypodermis)
What are the 5 layers of the epidermis?
S. basale S. spinosum S. granulosum S. lucidum S. corneum
What are corneocytes held together by?
corneodesmosomes
What are corneocytes?
Corneocytes are keratinocytes in their last stage of differentiation.
What happens to keratinocytes in to S. basale?
Keratinocytes in the stratum basale of the epidermis will multiply through cell division and migrate toward the skin surface. During migration keratinocytes will undergo multiple stages of differentiation to finally become corneocytes once they reach the stratum corneum.
How are corneocytes continually eliminated?
through desquamation or through rubbing, skin washing or detergents they are also continually formed through keratinocyte differentiation
How often are keratinocytes renewed?
Every 20-45 days BUT maintains the same thickness
What are the immune properties of keratinocytes?
produce interleukins, interferons and growth factors
How do the keratinocytes differ between then basal and corneum layers?
Basal = K5 and K14 Corneum = K1 and K10
What produces natural moisturising factor in the cells?
Filaggrin derived from pro-filaggrin
What does the NMF do?
helps maintain the skins hydration- keeps water inside the skin
NMF is also important in maintaining what type of environment at the outer surface of the S. corneum?
acid environment
How is the introduction of new cells in the basal layer of the epidermis balanced?
desquamation of mature corneocytes are shed from the surface of the S. corneum
What does desquamation involve?
degradation of the extracellular corner-desmosomes under the action of protease enzymes
What is the normal pH of the skin?
pH 5.5 - allows the protease to remain on the skin
What are lamella bodies?
derived from the Golgi apparatus of keratinocytes in the S. spinosum. From the site of production, lamellar bodies migrate to the top of the stratum granulosum and then into the intercellular domain of the stratum corneum to extrude their contents, which are predominantly lipids. The lipids ultimately form the lamellar lipid bilayer that surrounds corneocytes and also contribute to permeability barrier homeostasis of the stratum corneum.
Where are they located?
In the S. Spinosum of the epidermis
How is permeability barrier homeostasis maintained?
- Regulated by the calcium gradient in the epidermis.
- Usually the calcium level is very low in stratum corneum, but high in stratum granulosum.
If barrier is disrupted an influx of water occurs, which in increases the calcium levels in the stratum corneum but decreases it in the stratum granulosum. - This induces lamellar bodies to undergo exocytosis and secrete lipids such as glycosylceramides, cholesterol and phospholipids to retrieve the permeability barrier function of stratum corneum.
What is the function of the lipid lamellae layer?
to keep water inside the cell and allow irritant and allergens to bounce off
What is the brick wall model of the skin barrier?
corneocytes = bricks
corneodesmosomes = iron rods
lipid lamellae = cement
What enzymes break down the corneodesmosomes during desquamation?
depredatory proteases
Why is vitamin D essential in skin defence?
It produces the anti-microbial peptides necessary tp defend the skin from bacteria and viruses
What is the effect of irritants on the skin?
break down healthy skin
What is the effect of allergens on the skin?
they trigger skin flare ups by penetrating into the skin and causing the skin to react
What are skin-flare ups caused by?
allergens which have been able to penetrate into the skin, where they are met with lymphocytes with release chemicals that induce INFLAMMATION.
What is the cause of red skin?
dilation of blood vessels due to lymphocytes activity
What is the cause of itchy skin?
stimulation of nerves
What is the cause of dry skin?
skin cells leaking due to lymphocyte activity
What is the effect of pH on the skin?
If profilaggrin or filaggrin are absent there will be a lack of NMF» less water retention in the corneocytes
- pH will increase»_space; damaging skin barrier as the corneodesmosomes become damaged by the pH»_space; break down of skin barrier»_space; increased risk of infection
What happens in acne?
hypercornification of the stratum corneum»_space; corneodesmosomes block the entrance to hair follicles»_space; increased production of sebum by the sebaceous glands (greasy skin)»_space; some sebum gets trapped in NARROWED hair follicle»_space; sebum stagnates at the pit of the follicle where there is no O2»_space; provides anaerobic conditions which allow P.acnes to multiply
What are P.acnes?
propionic bacteria acnes
Why does acne lead to irritation and inflammation?
the p.acnes break down the triglycerides in sebum into free fatty acids»_space; inflammation and irritation
- and attraction of neutrophils since the p.acnes release chemicals that attract them
Why does pus form?
The immune system response causes a build up of oil, dead cells and bacteria within the pit of the hair follicle»_space; can lead to a local infection
What can trigger acne?
cosmetics and oily hair gel as they help ‘plug’ the hair follicle and initiate the acne process
What triggers further inflammation in acne?
the follicle is filled with attracted neutrophils
