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By
Jittipan Chavadej , Ph.D.
,
yr. 2000
Anatomy Dept.,Fac. of Science
Structural development
•begin as a single layer of
ectodermal cells
•formation of a thin outer layer
periderm at the end of the first
month
•third month- three layers
- basal layer, intermediate
layer&supl layer of peridermal cells
Diagram showing the formation of the skin at
various stages of development
•6th month -epidermis beneath
periderm differentiation into
the definitive layers
•Sloughs of peridermal cells into
the amniotic fluid
•Immigrant cells in the epidermis
-2nd month -melanoblast
-late in 1st trimester -Langerhans
cells
-Merkel cells
Melanoblast (-cyte) :
-derived from neural crest
-midpregnancy-begin producing
pigment granules = melanosomes
Dark skin-more pigment granules/cell
Albinism -genetic trait, lack of
enzyme-tyrosinase:tyrosine melanin
Epidermal differentiation
Movement of epidermal cells - loss
of adhesiveness e.g. fibronectin,
laminin&collagen types I&IV
Keratohyalin granules
(histidine&sulphur-
rich), (closely associated with keratin filament)-
stratum granulosum (keratinocyte)
Keratin filaments-stratum corneum
Lost nuclei -bag of
densely packed with
keratin filaments
•15-20 layers of dead
cells
Flattened cell-breaking
up nuclear membrane
Produce keratin filament
(desmosome)
Unspecialized cells
- mitotic activity
One of the prominent features of
thick skin=presence of epidermal
ridges and creases ->loops & whorls
Dermatoglyphics-basic patterns(epi.
ridge) for genetic analysis or
criminal investigation (unique to
individual)
Dermis
•Mesodermal cells from
dermatome / beneath ectoderm
•3rd month -transition from highly
cellular embryonic form
fibroblast +
fibrous
intercellular matrix
•Becomes highly vascularized +
sensory nerve
Future dermis-loosely aggregated mesenchymal cells
Epidermal appendages
Hair -induction from dermis
-12th week :down growth of
hair bud
-hair papillae hair shaft
epithelial hair sheath
-arrector pili muscle :dermal
root sheath & dermal papilla
-sebaceous gl.
fat-like
substance
hair follicle
Diagram showing development of a hair and a sebaceous gland
5th mo. hair shaft-keratinization
forming granules of
trichohyalin(hardness of the hair)
Late stage of hair formation-hair
bulb--> melanocytes -->color
Mammary Gland
•Mammary line or ridge(6 wk.) :base
of forearm region of hind limb
Small solid outbudding
lactiferous duct
formation+alveoli of the gland
epithelial pit (nipple-after
birth)
Diagram showing position
of mammary line
Stages in the embryonic development of
the human mammary gland
Abnormalities of Skin Development
•Ichthyosis-genetically transmitted
disorders of keratinization
Harlequin -autosomal recessive
disorder
•Hypertrichosis- formation of hair
follicle
•Atrichia -congenital absence of hair
A:milk line-mammary glands form along this line
B:common sites of formation of supernumerary nipples/mammary
gland
•Polythelia - accessory
nipples(axillary region)
•Polymastia -supernumerary brests