Skin - lecture 1

cutis = epidermis + dermis

skin = epidermis, dermis and subcutis

epidermis: no vessels, strat. sq. non-ker ep.

5 layers
- 1+2 = malpighi layer
- strat. granulosum → last living cell layer
- strat. lucidum → absent in thin skin
- strat. corneum → split into two: compactum and disjunctum
cells
- melanocytes
- dendritic processes are in contact w. cc. 36 keratinocytes
- most are clear → melanosomes are transferred to the keratinocytes by cytocrine secretion (why skin tans)
  - stimulated by UV-rad., TNF-alpha, ACTH and alpha-MSH
- melanin - tyrosine/tyrosinase reaction (mutation - albinism)
- darker skin: more large superficial melanosomes → not larger amount than in lighter skin, but size and placement change
- eumelanin: brown/black
- pheomelanin: red/yellow
- langerhans cell
- mononuclear-phagocyte system
- antigen-presenting cells
- merkel cell
- receptor
- keratinocyte
- 90 %
- basal: living cells, superficially: dead
- str. basale: mitotic act.
- prickle cells: desmosomes w. tonofilaments
- str.granulosum: profilaggrin providing clumping of tonofilaments in keratohyalin granules
  - release of EC lipids from lamellar bodies
- str. corneum
  - filaggrin + keratin filaments = KERATIN
  - cells lack nucl.
  - cornified envelope → involucrin protein (inner surface of the membrane)
  - cornified lipid envelope → ceramide
epidermal turnovertime : 52-75 days (in psoriasis around 8 days)

Dermo-epithelial junction

molecular anchorage
tonofilaments - desmosomes
basal cells - lamina densa (collagen IV + perlecan) - hemidesmosomes
- anchoring filaments attach the cells to lamina densa
anchoring fibrils of type VII collagen bind lamina densa to collagen fibers (type III) in papillary dermis
microfibrils link the elastic fibers to collagen fibers
skin diseases: nautoantibodies againts hemidesmosomes or specific proteins, coll. XVII, VII, etc. → formation of blisters, epidermolysis

dermis:

papillary layers
- loose CT
- fine collagen fibers (type I and III)
- capillary loop, nerve endings and meissner corpuscles
reticular layer: dense CT
- type 1 and elastic fibers
- smooth muscle cells in some cases such as tunica dartos of penis and scrotum
langer lines: long axis of rhomboids
- freq, coincide w, relaxed skin tension lines (kraissle´s lines)
dermal papillae
- friction ridges → fingerprint

subcutis: loose ct

mediates increased mobility of skin
panniculus adiposus: shock absorber, energy storage, thermal insulation
retinaculum cutis: strong binding to underlying tissues in certain areas of the skin
- in sole, palm and scalp: no significant sliding
very delicate in eyelids and forskin
skin turgor

skin appendages: hair and nail + glands

glands of the skin

sebaceous
- holocrine
- open into hair follicles, or skin surface: lips, inner surface of prepuce, minor labia, glans of penis/clitoris, areola/nippels
- missing in sole and palm
- branched alveolar
sudoriferous
- merocrine sweat
- open onto skin surface
- missing in lips, inner surface of prepuce, minor labia, glans of penis and clitoris
- cholinergic symp. act
- simple coiled tubular
- myoepithelial layer
odoriferous
- apocrine sweat
- open into hair follicles
- axillary, areolar, anal genital regions + (glands of moll and ceruminous glands (ear → cerumen ???))
- adrenergic symp. innervation
- simple coiled tubular
- myoepithelial layers

blood supply

arteriovenosus anastomoses or shunts
- against heat loss
- in certain areas of the skin ( fingertips, nose and ear)

dermatome

functions of the skin

receptor organ
thermoregulation
- passive: insulation by cubcutis
- active: sweat glands, vessels, m. arrector pili
photoprotection
- strat. corneum reflects UV rays
- melanin - scavanger of harmful free radicals
permeability barrier
- strat. corneum keratin and extracellular lipid + strat. granulosum tight junctions
- sealing aganist water loss
protection against pathogens
- sweat pH