By

Jittipan Chavadej , Ph.D.

Anatomy Dept.,Fac. of Scienceyr.,2

000

Structural development • begin as a single layer of ectode

rmal 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 int

o 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 producin g pigment granules = melanos

omes -Dark skin more pigment granules/cellAlbinism - genetic trait, lack of enz

-yme tyrosinase: tyrosine melanin

Epidermal differentiation - Movement of epidermal cells lo

ss of adhesiveness e.g. fibronect in, laminin&collagen types I&IV

Keratohyalin granules (histidine&sulph

- ur rich), (closely associated with keratin filamen

t)- stratum granulosum (keratinocyte)

Keratin filaments- stratum corneu m

Unspecialized cells- mitotic activity

Produce keratin filamen t (desmosome)

-Flattened cell breakin g up nuclear membra

ne

- Lost nuclei bag of de nsely packed with ker

atin filaments• - 1 5 2 0 layers of

dead cells

One of the prominent features of thick skin=presence of epidermal

- ridges and creases >loops & whorlsDermatoglyphics- basic patterns(

epi. ridge) for genetic analysis or c riminal investigation (unique to i

ndividual)

Dermis• Mesodermal cells from dermat

ome / beneath ectoderm

•3rd - month transition from highl y cellular embryonic form

fibroblast + fibrous intercellular matrix

• Becomes highly vascularized + sensory nerve

- Future dermis loosely aggregated mesenchymal

cells

Epidermal appendagesHair - 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 keratinizatio n forming granules of trichohyali

n (hardness of the hair)

- Late stage of hair formation hair-- --bulb > melanocytes >color

Mammary Gland

• Mammary line or ridge (6 wk.) :bas e of forearm

region of hind limb Small solid outbudding

lactiferous duct formation+alve oli of the gland

- epithelial pit (nipple after birth)

Stages in the embryonic developme nt of the humanmammary gland

Diagram showing posit

ion of mammary line

Abnormalities of Skin Development

•Ichthyosis- genetically transmitted disorders of keratinization

Harlequin - autosomal recessivedisorder

•Hypertrichosis- formation of hai r follicle

•Atrichia - congenital absence of hair

A: - milk line mammary glands form along this line

B: common sites of formation of supernumerary nipples/m ammary gland

•Polythelia - accessory nipples( axillary region)

•Polymastia - supernumerary brests