Skin Flashcards
Layers of skin
Epidermis
External layer: epithelial layer of ectodermal origin
STRAT SQ KERATINIZED epithelia (stratum basale, spinosum, granulosum, lucidum, corneum)
Dermis
Middle layer: mesodermal CT
Papillary layer: loose CT+ MEISSNER CORPUSCLE
Reticular layer: DENSE IRREG CT, SABECOUS GLANDS
Junction between epidermis and dermis has projections of dermis= dermal papillae+ invaginations of epidermis= epidermal ridges
Subcutaneous tissue / Hypodermis
Loose CT layers w pads of adipocytes
SWEAT GLANDS, HAIR follicles, and FIBRO-COLLAGENOUS BANDS ; VATER-PACINI CORPUSCLE
F: is to loosely bind the skin to underlying tissues corresponding to superficial fascia of gross anatomy
Skin main functions
Protective
- PHYSICAL BARRIER: against thermal+ mechanical insults like friction+ pathogens ; Epidermis has MELANIN protect against UV; Microorganism that penetrate skin alert APC (antigen presenting cells); Permeability barrier against water loss+ allows lipophilic drugs to be administered via skin patches
- SENSORY : Sensory RECEPTORS allow skin to monitor environment
- THERMOREG: Keeps constant body temp due to insulating layers FATTY layer, HAIR + SWEAT production; Heat loss by dense superficial microvasculature
- METABOLIC : Vitamin D3 synthesis through UV light on precursor- needed in Ca metabolism and bone formation
Excess ELECTOLYTES can be removed in sweat + subcutaneous tissue store energy in form of fat
- SEXUAL SIGNALLING: Features that indicate health skin+ hair
sex pheromones produced by apocrine sweat glands+ other
thick vs thin skin
Thick skin
400um-1.4mm
All layers visible; THICK stratum corneum
Palms+ soles
ECCRINE sweat glands: dermis+hypodermis; SIMPLE TUBULAR COILED GLANDS; secretory: clear+dark cells + myoepi cells. Duct has 2 layers STRAT CUBOIDAL EPI
Thin skin
75-150um; THIN stratum corneum + Indistinct stratum lucidum+ granulosum
ECCRINE
SABECOUS: HOLOCRINE secretion, DERMIS (NOT THICK), BRANCHED ACINAR GLANDS, SEBUM, duct in HAIR FOLLICLE or surface ( areola= vermilion zone, glans of penis+ cli meibomian gland In eyelid tarsal plate)
APOCRINE: DERMIS+HYPODERMIS (axilla, perineal, external genitalia, Moll glan eyelid, seromucous glands in external acoustic meatus canal); COILED TUBULAR GLANDS; ducts STRAT SQ EPI (2 layers) LARGER than eccrine, into hair follicle. secretion rich PROTEINS+PHEROMONES
Hair+ Everywhere else in body
Less abundant cells in epidermis
1) MELANOCYTES- NEURAL CREST derivatives
Migrate into developing stratum BASALE on basement membrane. They produce MELANIN which is PHAGOCYTOSED by KERATINOCYTES (contain more melanin).
- One melanocyte accumulates for every 5-6 basal keratinocytes 600-1200/mm^2 of skin
- PALE STAINING ROUNDED CELL BODIES attached by HEMIDESMOSOME to basal lamina but NO attachments to neighbouring keratinocytes
- Melanocytes contain MELANOSOMES (melanocyte granules) which store+ transport melanin
- UV causes keratinocytes to secrete PARACRINE FACTORS = stimulate melanocyte production and transformation to keratinocytes
- long IRREG CYTO EXTENSIONS of melanocytes between keratinocytes to TRASNFER MELANIN; between cells of stratum basale and spinosus which terminate w 5-10 keratinocytes
- Keratinocytes PHAGOCYTOSE tips of DENDRITES taking in melanosomes go to nuclei (via dynein)
- accumulate in keratinocytes and form SUPRANUCLEAR CAP before keratinization= absorb and scatter sunlight to protect DNA from UV
- Has small amount of mitochondria, short cisternae of RER, and well-developed GA
2) LANGERHANS cells = DENDRITIC cells= APC antigen-presenting cells
- in SPINOUS layer mostly; bone-marrow derived (monocytes); 2-8% cells in epidermis. Main function: ADAPTIVE immunity+ protection (present antigens to lymphocyte)
- DENSE layer in epidermis due to cytoplasmic processes from cells to keratinocytes
3) MERKEL’S cells= epithelial TACTILE cells
- MECHANORECEPTORS abundant in sensitive skin (fingertips +base of some hair follicle)
- Has KERATIN FILAMENTS located in stratum BASALE
- Joined by DESMOSOMES to keratinocytes in basal epidermal layer in thick+ thin skin. They resemble keratinocytes (common stem cell origin) but have FEW if any melanosomes
layers of epidermis
STRATUM CORNEUM
Most superficial layer, 20-30 layers of SQ keratinized, dead, FLAT, NON-NUCLEATED KERATINOCYTES
Keratinized cells have birefringent FILAMENTOUS KERATINS keratins: have 6 diff polypeptides from 40-70kDa made for differentiation
As they form KERATIN TONOFIBRILS become heavily massed w FILLAGRIN and other proteins in keratKERATOHYALINE GRANULES
After keratinization cells contain only AMORPHOUS FIBRILLARY proteins w PM surrounded by LIPID-RICH area. Fully keratinized /cornified cells now called SQUAMES which are shed on the surface when desmosomes +lipid rich cell envelope’s breakdown
F: Protects against water loss+ friction
stratum LUCIDUM
2-3 layers of dead, NON-NUCLEATED, KERATINIZED cells that are thin FLATTENED EOSINOPHILIC cells held together by DESMOSOMES. Only in THICK skin. KERATIN FILAMENTS embedded in electron dense matrix.
stratum SPINOSUM
3-5 layers of keratinocytes-flattened polyhedral cells.
- keratinocytes move upwards from stratum spinosum= DIFFERENTITATON begins w cells becoming filled w KERATOHYALINE granules (intensely BASOPHILIC+ w dense NON-MEMBRANE BOUND FILLAGRIN +other proteins associated w keratins of tonofibrils )
- small+ ovoid lipid containing LAMELLAR GRANULES (derived from GA)
- LIPID GRANULES have crucial sealing effect in skin responsible form BARRIER against foreign materials+ no water loss; key in evolutionary process of animals developing on land
- melanocyte processes
- LANGERHANS CELLS (APC)
Some of the cells leaving the stratum granulosum, and still bound together by desmosomes, undergo terminal differentiation and in thick skin appear as a dense thin layer – stratum lucidum:???
stratum BASALE
Low COLUMNAR/CUBOUDAL STEM cells (15-30 days) on BASEMNET MEMBRANE at dermal –epidermal junction. HEMIDESMOSOMES bind plasmalemma to basal lamina + DESMOSOMES binds cells laterally.
- (like spinosum) synthesis of epidermal keratinocyte cells
- Has IF-keratins (increase amount of cells giong upward)
- MERKEL’S cells + MELANOCYTES
Dermis
CT that supports epidermis + binds to subcutaneous tissue. Thickness varies (back its 4mm)
Has irreg projections= dermal papillae that interdigitate w projections of epidermis (epidermal ridges)
Dermal papillae more numerous in skin subjected to frequent pressure where enforces dermal-epidermal junction
Between basal layer of epidermis + papillary layer of dermis = basement membrane (basal+ reticular lamina)
- Nutrients for keratinocytes must diffuse into avascular epidermis through dermis vasculature through basement membrane
1) papillary layer- outermost, thin loose CT w type I+III collagen fibres, fibroblasts and other cells of CT (mast cells+ macrophages+ leukocytes+ dendritic cells) forms major part of dermal papillae
- Papillary layer has anchoring fibrils of VII to attach to basal lamina = help bind dermis to epidermis
2) denser reticular layer- thicker w dense CT; has more fibres but fewer cells than papillary layer. Network of elastic fibres which eventually degenerate due exposure to sun. Between the collagen (I)+ elastic fibres abundant proteoglycans rich in dermatan sulfate
Vasculature + Innervation
Vasculature
Dermal regions have rich network of blood +lymphatic vessels. Nutritive vessels forms 2 plexus
1) between papillary+ reticular dermal layers = subpapillary plexus
- Capillary branches extend into dermal papillary forming rich network below epidermis
2) near interface of dermis+ subcutaneous tissue= deep plexus w larger blood+ lymphatic vessels.
Lymphatic vessels in dermis begin in dermal papillae and also form 2 plexus
Dermis also has arteriovenous anastomosis have a thermoregulatory function= decrease blood flow in papillary layer to minimize heat loss in cold conditions vise versa
Innervation
Dermis highly innervated 1) sensory afferent nerve fibres form network in papillary dermis + around hair follicles; end in epithelial+ dermal receptors
2) Postganglionic fibres of sympathetic ganglia to dermal sweat glands+ smooth m fibres
Hair
hair is ELONGATED KERATINIZED structure made by hair follicle.
medulla: vacoulised cells THICK HAIR
cortex: CUBOIDAL cells differention -> HARD KERATIN (keratin filled cells)
cuticle: SQUAMOUS cells
3 parts: hair bulb, root and shaft
- hair follicle: INVAGINATION EPIDERMIS
GERMINATIVE layer: adj to papilla for division+prolif melanocytes
CORTEX: CUBOIDAL cells differention -> HARD KERATIN (keratin filled cells)
MEDULLA: vacoulised cells THICK HAIR
INTERNAL ROOT SHEATH: form germinative; cuticle, HEXLEY’S+ HENRYS layer
EXTERNAL ROOT SHEATH: continuous w BASAL+SPINOUS layer.
GLASSY MEMBRANE: continuous w BASEMENT MEMBRANE of epidermis
CT SHEATHCUTICLE SQUAMOUS cells
- Hair Bulb
DERMAL PAPILAE (terminal dilation of hair follicle)+ LOOSE CT + capillaries
nipple
BASAL layer, heavily PIGMENTED w DENSE CT
EPIDERMAL ridges deeply intergitating w DERMAL PAPILLAE
sabecous glands open at surface
free nerve ending+ MEISSNER CORPUSCLE
bundles SMOOTH M along lactiferous ducts
nail
LUNULA crescent shape white area; colour from opaque nail matrix + immature nail plate below
HYPONYCHIUM: free end of nail plate is, bound to epidermis
saggital section
- PROXIMAL NAIL FOLD
- EPINOCHYIUM= cuticle
- NAIL ROOT+PLATE
- DORSAL NAIL MATRIX
- NAIL BED
- DERMIS
Sensory receptors
FREE NERVE ENDING: epidermis; pain+ temp+ itch
ROOT HAIR PLEXUS: fibres around hair follicles bases, hair mov
MERKEL’S CELLS: epidermis; ight touch+ obj shape
MEISSNER CORPUSCLE: papillary layer; encapsulated; light touch
RUFFINI CORPUSCLE: reticular area; encapsulated; skin stretch+torque
KRAUSE BULB ENDING: encapsulated; low freq vibrations
PACICIAN COPUSCLE: reticular layer+ hypodermis; encapsulated+ lamellated; Pressure+ firm touch +vibration
