Histology Of The Skin

Endre Dobó

types of the skin > hairy skin / thin skin > has hair follicles > has thin epidermis > nonhairy skin / glabrous skin / thick skin > has NO hair follicles > has thick epidermis > occurances > both sexes > palm > sole > lips > man > glans penis > prepuce / foreskin > woman > clitoris > labium minus (pudendis) > internal surface of labium majus > nipple and areola

> protection against > mechanical insults > solar radiation (the sun's UV rays) > chemical insults > invasion by micro-organisms > insulation against heat loss > thermoregulation > sensation > see tactile and cold/heat receptors > prevents extreme water loss by evaporation > secretion > see mammary glands > excretion > of certain waste products through sweat glands > production of vitamine D3 > store of energy

epidermal derivatives > hair (pilus) > special hairs as to their anatomical sites, e.g. > hears of head (capillus / pilus capitis) > eyelash (cilium) > pubic hair (pubes) > vibrissa (hair of vestibule of nose) > nail (unguis) > glands > sebaceous gl. (gl. sebacea) > e.g. tarsal gl. / gl. of Meibom > sweat gl. (gl. glomiformis / gl. sudorifera) > apocrine sweat glands > merocrine / eccrine sweat glands

> epidermis > stratified squamous keratinized epithelium > epidermal ridges project underneath > dermis / corium > loose and irregular dense connective tissue > dermal papillae expands into the epidermis > capillary loops are comprised here > mechanoreceptors may be present > hypodermis / subcutaneous tissue > loose connective tissue with many fat cells > also referred to as superficial fascia of gross anatomy

str. corneum

str. lucidum

epidermis

str. granulosum str. polygonale

str. basale

str. papillare

dermis str. reticulare

str. reticulare

dermis

adipocytes

collagen fibers Paccinian corpuscule

hypodermis

(from external) > str. corneum > horny cells in various thickness > str. lucidum > may be absent from thin skin > eosinophilic flattened cells in HE preparations > str. granulosum > is composed of up to five layers of cells > contains strongly basophil keratohyaline granules > str. spinosum / str. polygonale > is of various thickness; is composed of cuboidal cells > str. basale / str. germinativum / str. cylindricum > single layer of cells, most of which are precursor cells > cells are attached to the basement membrane with hemidesmosome layer of Malphigi / Malphigian layer > where cell divisions occur (there are mitotic figures): str. spinosum and str. basale, together

> keratinocytes > cf. keratocytes are present in the cornea!!! > have desmosomes > contain cytokeratin intermediate filaments (str. basale and spinosum), which constitute tonofibrils > produce lamellar bodies formed by lipid bilayers (str. spinosum), which diminish the evaporation of water > contain keratohyaline granules (str. granulosum), which form soft keratin together with tonofilaments > may take up melanin pigment from melanocytes > accumulation of soft keratin leads to cell death (str. mortificatum: str. lucidum and str. corneum)

> Langerhans cells > 2-3% of the epidermal cells > are present in the str. basale and spinosum > lack desmosomes > derive from the monocytes > antigen-presenting cell (professional dendritic cells) > express MHC II molecules > activated cells migrate to the near lymph nodes > members of the SALT ( skin-associated lymphatic tissue ) > Merkel cells > secondary sensory epithelial cells > are responsible for the discriminative touch > are present within the str. basale > are bound to the neighbouring cells with desmosomes

> melanocytes > are derived from neural crest cells > are scattered in the str. basale > have round cell bodies with long irregular extensions > lack desmosomes to the adjacent keratinocytes > have hemidesmosomes to the basal lamina > have membrane-bound vesicles (melanosoma) with melanin granules > rate-limiting enzyme of melanin synthesis is the tyrosinase > albinos have the normal number of melanocytes, but lack the enzyme > solar radiation facilitates activity of the enzyme > melanin provides a protective barrier to the ultraviolet radiation in sunlight > melanin granules are transfered into keratinocytes > ratio of melanocytes and keratynocytes: 1/4-1/10

> layers > str. papillare / pars papillaris > this extends into the epidermis as dermal papillae, which may contain: > capillary loops or > encapsulated nerve endings > e.g. Meissner s tactile corpuscule (mechanoreceptor) > loose connective tissue > str. reticulare / pars reticularis > irregular dense connective tissue > characteristic histological items > glomus bodies: control the arteriolovenular anastomosis shunts > hair follicles > sebaceous glands > apocrine and eccrine sweat glands > Paccinian corpuscules

str. granulosum epidermal ridge dermal papilla str. reticulare eccrine sweat gland (excretory duct)

peripheral nerve

Paccinian corpuscules

str. lucidum str. papillare

str. reticulare eccrine sweat gland (excretory duct) collagen fibers

> hair (pilus) > hair root (radix pili) [1] > hair shaft (scapus pili) [2] > hair medulla > hair cortex > hair cuticle

[5] [7]

> hair follicle (folliculus pili) > hair bulb (bulbus pili) [3]

[6]

[4] [2]

> hair papilla (dermal papilla) > hair matrix

> isthmus [4] > segment between the arrector pili m. and opening of the sebaceous gland

> infundibulum [5] > accessories of the hair follicles > glands > sebaceous glands [6] > apocrine sweat glands > arrector pili m. [7]

[1] [3]

epidermis str. reticulare hair follicle: infundibulum m. arrector pili

hair follicle : sebaceous glands hair follicle : hair bulb

eccrine sweat gland (excretory duct)

collagen fibers

( oblique section)

external root sheath internal root sheath cortex of future hair medulla of future hair

hair matrix dermal papilla membrana basalis connective tissue sheath

arrows: peripheral nerves

perineurium

peripheral nerves

Boundary between the dermis and hypodermis (Sudan Red and hematoxylin)

arrows: mast cells

> apocrine sweat glands > common apocrine sweat glands on specific sites > glands of armpit > circumanal glands ( odoriferous glands ) > ciliary glands (Moll s glands) > ceruminous glands (wax-secreting glands in the ear canal) > modified apocrine sweat glands (i.e. they open free from hair follicles) > mammary glands > sebaceous glands > common sebacous glands on specific sites > glands of Zeiss > modified sebacous glands (i.e. they open free from hair follicles) > tarsal glands (Meibomian glands) > Tyson's glands on the foreskin > glands of the labium minus > rare ectopic glands of the upper lip ( Fordyces spots ) > glands on the nipple and the areola

> subpapillary plexus > at the boundary of the sublayers of the dermis > gives rise to the capillary loops of the dermal papillae > arteriovenous anastomosis / arteriolovenular shunt > glomus bodies > structure > the afferent arteriole is branched and convoluted > have relatively thick wall and small lumen > richly innervated with sympathetic nerve fibers > function > bypass-regulating mechanism in the flow of blood > cutaneous plexus > at the boundary of the dermis and hypodermis