Skin Structure Flashcards
Function of skin
-protection: mechanical impacts, pressure, variation in temperature, microorganisms, radiation/ chemicals
- physiological regulation: body temperature via sweat and hair, changes in peripheral circulation, fluid balance via sweat, synthesis of vit D
- sensation: network of nerve cells that detect and flat changes in the environment
Epidermis
- basement membrane: sheet like layer of extra cellular matrix proteins
- stratum basale: cuboidal/ low columnar cells, mitotically active, constant regeneration of the other layers, connected to BM by hemidesmosomes
- stratum spinosum: polyhedral keratinocytes, rich in desmosomes
- stratum granulosum: cells becoming flattened, contain keratohyalin granules, starting to lose nucleus and cytoplasm
- stratum corneum: large flat plat like envelopes filled with cross linked keratin, lipids
dermis
- connective tissue
- collagen type 1 ( provides tensile strength)
- elastin ( allows stretch)
- two layers- papilary layer and reticular layers
- fibroblasts- synthesis collagen, elastin, ground substances
sensory organ
Free nerve endings in the skin
-papillary dermis and form attachments with Merkel cells act as mechanoreceptors
-Meissner’s corpuscles:
rapidly acting mechanoreceptors responsible for touch.
Papillary dermis of hands and feet
-Pacinian corpuscles
detect deep pressure and vibration usually in subcutis
keratinocyte
location- keratinised stratified squamous epithelium
function- protection and barrier, vitamin D production
stem cell
location- stratum basale
function- self reveal and repopulation of epidermal layers
merkel cells
location- epidermis (mostly basel layer)
function- sensation
langerhans cell
location- epidermis (mostly stratum spinous) and upper dermal layer (papillary)
function- dendritic cells
melanocyte
location- basal layer
function- protection from radiation
UV light
Chronic UV exposure in humans leads to:
-Loss of skin elasticity / fragility,
-Abnormal pigmentation
-Haemorrhage of blood vessels
-Wrinkles and premature ageing
keratins
location- all epidermis layers
function- major structural protein, intermediate filaments
keratohylain granules- profilaggrin
-converted to filaggrin which aggregates keratin filaments into tight bundles
keratohyalin granules- involucrin
-formation of a cell envelope around cells in the stratum corneum
keratohyalin granules- Ioricin
cross links to involucrin
polysaccharides, glycoproteins, lipids
location- lamellar granules
function- extrude into intercellular space; form the “cement” that holds together the stratum corneum cells
mast cells
-Produce inflammatory mediators (eg, histamine, heparin) & chemotactic factors for eosinophils and neutrophils
inflammation/vascular phase
-24-48 hours
-Platelets initiate haemostasis/blood clot and also the healing cascade.
-Attracts other cells to the wound to fight infection and transition from inflammation to repair (neutrophils/macrophages).
characteristic signs of inflammation: red/swelling
-Neutrophils and macrophages phagocytose dead tissue and microorganisims
proliferative phase
- Re-epithelialisation:
Within 1-2 days of wounding, epithelial cells loosen cell-cell adhesions and migrate to the wound site, cover the granulation tissue, and then meet in the middle.
Once the wound is covered in a single layer of keratinocytes all keratinocytes start to proliferate.
2. Formation of granulation tissue;
mainly type III collagen
3. Neovascularisation: proliferation and migration of endothelial cells
remodelling phase
Granulation tissue becomes mature
scar tissue
Collagen is organised into thick
bundles and extensively
cross-linked to form a mature scar
Switch in type III collagen to
type I collagen
Final strength only 70-80% of
preinjured skin
Scar strength 5% at 1 week,
20% at 3 weeks and
70-80% at 1 year
EGF (epidermis growth factor)
-Re-epithelialisation
(keratinocyte proliferation and migration)
Platelet- derived growth factors (PDGF)
-Matrix formation (increased numbers and activity of fibroblasts)
-Remodelling (production of proteases)
Vascular endothelial growth factors
- angiogenesis (endothelial cell proliferation and migration)
IL1/6 and Tumour necrosis factor alpha
function- inflammation
factors affecting wound healing- local factors
- infection
- foreign body
- oxygenation
- vascular supply
