The Integumentary SystemThe Integumentary System

The Integumentary SystemThe Integumentary System Consists of skin & Consists of skin & Its derivatives:Its derivatives:

Sweat glandsSweat glands Sebaceous Sebaceous

glandsglands Arrector pili Arrector pili

musclesmuscles NailsNails HairHair Mammary glandsMammary glands

Development of SkinDevelopment of Skin

Skin consists of Skin consists of two layerstwo layers that are that are derived from two different germ derived from two different germ layerslayersEpidermisEpidermis, superficial epithelial , superficial epithelial

tissue derived from tissue derived from surface surface ectodermectoderm

DermisDermis, deeper layer of connective , deeper layer of connective tissue derived from the tissue derived from the mesodermmesoderm

EpidermisEpidermis In the In the 4-5th week4-5th week, the skin of , the skin of

the embryo consists of simple the embryo consists of simple cuboidal epithelium….the cuboidal epithelium….the surface ectodermsurface ectoderm

By the By the 7th week7th week, the surface , the surface ectodermal cells proliferate ectodermal cells proliferate and form a layer of squamous and form a layer of squamous epithelium, the epithelium, the peridermperiderm (epitichium) and a (epitichium) and a basal basal germinative layer. germinative layer.

During During 11stst & 2 & 2ndnd trimesters trimesters, , epidermal growth occurs in epidermal growth occurs in stages, which result in an stages, which result in an increase in epidermal increase in epidermal thicknessthickness

PeridermPeriderm The peridermal cells The peridermal cells

continually undergo continually undergo keratinization and keratinization and desquamation and are desquamation and are replaced by cells arising from replaced by cells arising from the the basal layerbasal layer

The exfoliated cells form part The exfoliated cells form part of the white greasy of the white greasy substance, the substance, the vernix vernix caseosacaseosa, that covers the , that covers the body of the fetusbody of the fetus

Replacement of peridermal Replacement of peridermal cells continue untill about the cells continue untill about the 2121stst week week, thereafter the , thereafter the periderm disappears and the periderm disappears and the stratum corneumstratum corneum forms forms

Basal Germinative LayerBasal Germinative Layer This layer becomes the This layer becomes the

stratum germinativumstratum germinativum of the epidermisof the epidermis

It proliferates and the It proliferates and the new cells are displaced new cells are displaced into the layers into the layers superficial to it.superficial to it.

By By 1111thth week week, an , an intermediate layerintermediate layer, , containing several cell containing several cell layers, is interposed layers, is interposed between the basal cells between the basal cells and the periderm.and the periderm.

Basal Germinative Layer cont’dBasal Germinative Layer cont’d

Proliferation of stratum Proliferation of stratum germinativum also forms germinativum also forms epidermal ridgesepidermal ridges which which extend into the extend into the developing dermis. developing dermis.

These ridges begin to These ridges begin to appear in embryo of appear in embryo of 10 10 weeksweeks and are and are permenantly established permenantly established by the by the 1717thth week week..

These ridges produce These ridges produce grooves on the surface of grooves on the surface of palms of the hand and palms of the hand and soles of the feet including soles of the feet including digitsdigits

Melanoblasts & MelanocytesMelanoblasts & Melanocytes During the early fetal During the early fetal

period the epidermis is period the epidermis is invaded by invaded by melanoblastsmelanoblasts, cells of , cells of the neural crest origin.the neural crest origin.

Melanoblasts move to Melanoblasts move to dermoepidermal dermoepidermal junctionjunction and and differentiate into differentiate into melanocytesmelanocytes

The melanocytes have The melanocytes have several long processes.several long processes.

Melanoblasts & Melanocytes cont’dMelanoblasts & Melanocytes cont’d

The The cell bodiescell bodies of of melanocytes are melanocytes are confined to the confined to the basal basal layerslayers of the of the epidermis, and their epidermis, and their processes extend processes extend between the between the epidermal cells epidermal cells

The melanocytes begin The melanocytes begin producing producing melaninmelanin before birthbefore birth and and distribute it to the distribute it to the epidermal cellsepidermal cells

At birth all At birth all layers of the layers of the adult epidermis adult epidermis are presentare present

DermisDermis The The dermisdermis is derived from is derived from

the mesenchyme the mesenchyme underlying the surface underlying the surface ectodermectoderm

This mesenchyme is derived This mesenchyme is derived from the:from the: Somatic layer of the Somatic layer of the

lateral mesodermlateral mesoderm (most (most of it)of it)

Dermatomes of the Dermatomes of the somitessomites (some) (some)..

By By 1111thth week week, the mesenchymal , the mesenchymal cells begin to produce cells begin to produce collagenous and elastic collagenous and elastic connective tissue fibersconnective tissue fibers

Dermal PapillaeDermal Papillae

As the epidermal As the epidermal ridges are formed, the ridges are formed, the dermis projects dermis projects upward into the upward into the epidermis and forms epidermis and forms the the dermal papillaedermal papillae

Capillary loops and Capillary loops and sensory nerve endings sensory nerve endings develop in these develop in these papillaepapillae

DP DP

HairHair Begin to develop during Begin to develop during

the the 3rd month3rd month, but they , but they do not become visible do not become visible until the until the 2020thth week week

Begins as an epidermal Begins as an epidermal proliferation, the proliferation, the hair budhair bud, , into the underlying into the underlying dermis.dermis.

The deepest part of the The deepest part of the hair bud becomes cup-hair bud becomes cup-shaped, forming a shaped, forming a hair hair bulbbulb

The hair bulb gets The hair bulb gets invaginated by invaginated by mesenchymal mesenchymal hair papillahair papilla

Hair cont’dHair cont’d The The central central epithelial cells epithelial cells

of the hair bulb give rise of the hair bulb give rise to the shaft of the to the shaft of the hair, hair, that grows through the that grows through the epidermis and protrudes epidermis and protrudes above the surface of the above the surface of the skin skin

The The peripheral peripheral cells of the cells of the hair bulb form the hair bulb form the epithelial root sheathepithelial root sheath..

The cells of the epithelial The cells of the epithelial root sheath proliferate to root sheath proliferate to form a form a sebaceous gland sebaceous gland budbud..

Hair cont’dHair cont’d Surrounding Surrounding

mesenchymal cells mesenchymal cells differentiate into differentiate into dermal root dermal root sheathsheath. .

The The arrector pili arrector pili musclemuscle differentiates differentiates from the surrounding from the surrounding mesenchymemesenchyme

Melanoblasts Melanoblasts migrate migrate into the hair bulb and into the hair bulb and differentiate into differentiate into melanocytesmelanocytes

Hair cont’dHair cont’d

Hairs are first recognizable in the Hairs are first recognizable in the region of region of eyebrows, upper lip and eyebrows, upper lip and chinchin

The first set of hairs that appear are The first set of hairs that appear are fine and colorless and are called fine and colorless and are called ‘lanugo’‘lanugo’ hair hair

Lanugo hair are replaced during the Lanugo hair are replaced during the perinatal periodperinatal period by coarser hair by coarser hair

Sweat GlandsSweat Glands Develop at about Develop at about 20 20

weeksweeks as solid growth of as solid growth of epidermal cellsepidermal cells into the into the underlying dermisunderlying dermis

Its terminal part Its terminal part coilscoils and and forms the forms the body of the body of the glandgland

The The central cellscentral cells degenerate to form the degenerate to form the lumen of the glandlumen of the gland

The The peripheral cellsperipheral cells differentiate into differentiate into secretory cellssecretory cells and and contractile myoepithelial contractile myoepithelial cellscells

Vernix CaseosaVernix Caseosa Vernix caseosaVernix caseosa, is the waxy , is the waxy

or cheesy white substance or cheesy white substance found coating the skin of the found coating the skin of the newborn. newborn.

The vernix is secreted by the The vernix is secreted by the sebaceous glands around the sebaceous glands around the 20th week of gestation20th week of gestation

It is composed of:It is composed of: SebumSebum (the secretion of (the secretion of

the sebaceous glands)the sebaceous glands) Desquamated epithelial Desquamated epithelial

cells cells Fetal hair (lanugo hair)Fetal hair (lanugo hair)

It protects the baby's skin It protects the baby's skin from dehydation and from from dehydation and from constant exposure to the constant exposure to the amniotic fluid. amniotic fluid.

NailsNails

Begin to develop at Begin to develop at about about 10th week10th week of of gestation, as thickened gestation, as thickened areas of the epidermis at areas of the epidermis at the the tips of the digits. tips of the digits.

Later, these nail fields Later, these nail fields extend to the extend to the dorsal dorsal surfacesurface and become and become surrounded by the surrounded by the nail nail foldsfolds. .

Cells from the Cells from the proximal proximal nail foldnail fold grow over the grow over the nail field and form nail field and form keratinized nail platekeratinized nail plate, the , the primordium of the nail.primordium of the nail.

The MThe Mammaryammary GlandsGlands Begin to develop Begin to develop

during the during the 6th week6th week as thickened strips of as thickened strips of the the ectodermectoderm ((mammary ridgesmammary ridges) ) that extend from the that extend from the axillary to the inguinal axillary to the inguinal regions.regions.

They They regressregress in most in most locations locations except in except in the area of the the area of the pectoral musclepectoral muscle, , where they where they proliferate. proliferate.

The MThe Mammaryammary Glands cont’dGlands cont’d The downgrowth of The downgrowth of

epithelial tissueepithelial tissue continues to continues to proliferate into 16 to proliferate into 16 to 24 solid outbuddings 24 solid outbuddings which give rise to the which give rise to the lactiferous ducts. lactiferous ducts.

Fibrous connective Fibrous connective tissue and fat of the tissue and fat of the mammary gland mammary gland develop from the develop from the surrounding surrounding mesenchyme.mesenchyme.

The lactiferous ducts The lactiferous ducts at first open into a at first open into a small small mammarymammary pit pit. .

Postnatal DevelopmentPostnatal Development

A.A. NewbornNewborn (nipple is (nipple is inverted)inverted)

B.B. ChildChild (nipple elevates (nipple elevates to form the usual to form the usual nipple)nipple)

C.C. PubertyPuberty (breast (breast enlarges due to enlarges due to development of the development of the mammary glands) & mammary glands) & deposition of fatdeposition of fat

D.D. Late pubertyLate puberty

E.E. Young adultYoung adult

F.F. Pregnant femalePregnant female

AnomaliesAnomalies

GynecomastiaGynecomastiaPolytheliaPolythelia Inverted nipplesInverted nipples