skin physiology and histology Flashcards
what 3 factors make the skin a waterproof barrier?
- keratin
- tight junctions
- lipids
what 3 factors make the skin a physical barrier to trauma?
- tight junctions in keratinocytes to resist frictional forces
- stratified epithelium resists abrasive forces
- fat in subcutis acts as shock absorber
what are the tissue resident macrophages in skin?
langerhans cells
what do langerhans cells do in an immune response?
= antigen presenting macrophages
- migrate from epidermis to dermis
- active a T cell response
what do keratinocytes do in an immune response?
- proliferate
- secrete cytokines
what type of sensation do merkle cells respond to?
light touch
what are the 2 types of mechanoreceptors in the dermis? what sensations do they respond to?
- pacinian corpuscles → pressure/vibration
2. meissner corpuscles → touch
how is the skin an energy store?
subcutaneous fat
- acts as an insulator, shock absorber AND energy storer
white adipose connective tissue
how can UV affect skin?
- burns
- suppress action of langerhans cells
- damage DNA (skin cancer)
which vitamin is produced and stored in the skin? In which layers?
vitamin D
- produced In the superficial layers of the skin + stored In the deeper layers
How is Vitamin D synthesised?
UVB light
cleaves 7-dehydrocholestrol to pre vitamin D3 (cholecalciferol)
Vit D2 from supplements & D3 in diet
hydrolysed in liver into 25-hydroxy vitamin D (ie. calcifediol)
hydrolysed in kidney to 1,25 hydroxy vitamin D (ie. Calcitriol)
how is the skin involved in thermoregulation?
The amount of blood flow to the skin determines the degree of heat loss and, therefore, the core body temperature.
how many layers are there of the skin?
3
epidermis
dermis
subcutaneous tissue (fat)
what is the epidermis?
- the outer layer of skin
- an epithelial layer resting on a BM made of type 4 collagen
what are the 4 layers of the epidermis?
- stratum corneum (outermost)
- stratum lucidum
- stratum granulosum
- stratum spinousum
- stratum basale (innermost)
what are the epidermal adnexae?
- they are specialised down growths of the epidermis into the dermis
give 4 examples of epidermal adnexae structures?
- hair follicles
- sebaceous glands
- eccrine sweat glands
- apocrine sweat glands
what are sebaceous glands?
- accompany hair follicles in dermis
- produce sebaceous secretions which lubricate and waterproofs hairs via HOLOCRINE secretion
what are eccrine sweat glands?
- most common sweat glands
- coiled tubes
- in dermis
what are apocrine sweat glands
- specialised sweat glands found in groin, armpits, genitals, anus, external auditory canal (produce ear wax)
describe the shape of the demo-epidermal junction?
- ridged
- has pegs
- these act as anchors
where is the subcutis layer of skin?
beneath the dermis
where is melanin synthesised?
in the melanosomes of melanocyte cells
found in the stratum basale of the epidermis
what are melanocytes derived from.?
melanocytes are derived from tyrosine
what is the role of melanin?
absorbs UV (A&B) + protects from non-ionising radiation
what is the distinguishing feature of the stratum corneum
acellular
what is the distinguishing feature of the stratum granulsoum
where keratin forms
flattened squames
what is the distinguishing feature of the stratum spinosum?
has keratinocytes
what is the distinguishing feature of the stratum basale?
melanocytes and stem cells
so cell growth only in this layer
when is more melanin produced?
when exposed to more UVB ie. tanning
what is the purpose of the dermis layer?
what is it made of ?
- made of gland and connective tissue (thick and elastic)
- allows for strength and flexibility
what are the 2 different pigments produced by melanocytes?
black eumelanin
red pheomelanin
what hormones are produced by skin?
IGF1 (insulin like growth factor)
vit D3 (actually a hormone)
define emollients
trap moisture in skin allowing tit to rebuild
define humectants
- trap moisture and maintain low pH
how is acne caused?
Hypercornification of skin: this blocks the hair follicle entrance
(ie. over build up of dead cells )
therefore the sebum (oily substance produced by the sebaceous glands ) gets trapped in the narrow hair cells
bacteria multiply in anaerobic conditions
cause irritation, inflammation and attract neutrophils
what cells make up the skin barrier on the stratum corneum?
corneocytes - dead/termianted keratinocytes
what are 3 components that make up the skin barrier?
- lipid lamellae - water barrier the tallows cells to swell
- NMF within corneocytes maintains low pH and regulates in/out of cell (water/allergens)
- corneodesmosomes - link corneocytes together
what protein forms NMF?
profilaggrin to fillagrin reaction produces NMF
what is desquamation?
when your skin peels as a result of shedding corneocytes
why does desquamation happen?
degrading proteases
break down the corneodesmosomes that hold the corneocytes together
barrier breaks down
cells shed
how is desquamation prevented?
proteases inhibitors
are used to prevent degrading proteases from breaking down the barrier
only work at low pH therefore important that pH5/5.5 is maintained by NMF
