Int-Development of the iNTEGUMENTARY.pptx

Development of the INTEGUMENTARY SYSTEM (Cont’d) ANA 204 SYSTEMIC EMBRYOLOGY I AYOADE, O. H 1 EPIDERMIS  The primordium (i.e Early stage) of the epidermis is the layer of surface ectodermal cells ...

Development of the INTEGUMENTARY SYSTEM (Cont’d) ANA 204 SYSTEMIC EMBRYOLOGY I AYOADE, O. H 1 EPIDERMIS  The primordium (i.e Early stage) of the epidermis is the layer of surface ectodermal cells  These cells proliferate and form: ◦ a peridermal layer of squamous epithelium ◦ a basal (germinative) layer 2 EPIDERMIS (Periderm)  The cells of the periderm continually undergo keratinization and desquamation and are replaced by cells arising from the basal layer  The exfoliated peridermal cells form part of the white greasy substance-vernix caseosa- that covers the fetal skin 3 EPIDERMIS (Periderm) *  Later, the vernix (Latin: varnish) contains sebum, the secretion from sebaceous glands (check slide 20) 4 EPIDERMIS (Periderm)  Thevernix protects the developing skin from:  constant exposure to amniotic fluid, with its high urine content, during the fetal period.  In addition, the greasy vernix facilitates birth of the fetus. 5 EPIDERMIS (Basal Layer)  Thebasal layer of the epidermis becomes the stratum germinativum 6 EPIDERMIS (Basal Layer)  The basal layer of the epidermis becomes the stratum germinativum  Stratum germinativum produces new cells that are displaced into the more superficial layers  By 11 weeks, cells from the stratum germinativum have formed an intermediate layer 7 EPIDERMIS (Basal Layer) 8 EPIDERMIS (Basal Layer)  Replacement of peridermal cells continues until approximately the 21st week  After 21st week, the periderm disappears and the stratum corneum forms. 9 EPIDERMIS (Basal Layer)  Proliferation of cells in the stratum germinativum also results in:  Formation of epidermal ridges, which extend into the developing dermis 10 EPIDERMIS (Basal Layer)  These ridges begin to appear in embryos at 10 weeks and are permanently established by 17 weeks  The epidermal ridges produce grooves on the surface of the palms and the soles, including the digits (fingers and toes  The type of pattern that develops is determined genetically and constitutes the basis for examining fingerprints in criminal investigations and medical genetics 11 EPIDERMIS (Cont’d)  The transformation of the surface ectoderm into a multilayered epidermis results from continuing inductive interactions with the dermis.  Skin is classified as thick or thin based on the thickness of the epidermis. ◦ Thick skin :covers the palms and soles; it lacks hair follicles, arrector muscles of hairs, and sebaceous glands, but it has sweat glands. ◦ Thin skin: covers most of the rest of the body; it contains hair follicles, arrector muscles of hairs, sebaceous glands, and sweat glands 12 EPIDERMIS (Cont’d)  Late in the embryonic period, neural crest cells migrate into the mesenchyme of the developing dermis and differentiate into melanoblasts  Laterthese cells migrate to the dermoepidermal junction and differentiate into melanocytes  This involves the formation of pigment granules 13 EPIDERMIS (Cont’d)  Melanocytes appear in the developing skin at 40 to 50 days, immediately after the migration of neural crest cells  In white races, the cell bodies of melanocytes are usually confined to basal layers of the epidermis;  however, their dendritic processes extend between the epidermal cells 14 EPIDERMIS (Cont’d)  Only a few melanin-containing cells are normally present in the dermis  The melanocytes begin producing melanin (Greek [Gr]. melas, black) before birth and distribute it to the epidermal cells  Pigment formation can be observed prenatally in the epidermis of dark-skinned races;  however, there is little evidence of such activity in light-skinned fetuses 15 EPIDERMIS (Cont’d)  Increasedamounts of melanin are produced in response to ultraviolet light.  Therelative content of melanin inside the melanocytes accounts for the different colors of skin.  The transformation of the surface ectoderm into a multilayered epidermis results from continuing inductive interactions with the dermis 16  DERMIS (Mesenchyme) 17 DERMIS  The dermis develops from mesenchyme, ◦ which is derived from the mesoderm underlying the surface ectoderm 18 DERMIS  Most of the mesenchyme that differentiates into the connective tissue of the dermis originates from: ◦ the somatic layer of lateral mesoderm; ◦ some of it is derived from the dermatomes of the somites By 11 weeks, the mesenchymal cells have begun to produce collagenous and elastic connective tissue fibers As the epidermal ridges form, the dermis projects into the epidermis, forming dermal ridges that interdigitate with the epidermal ridges 19 DERMIS 20  DERMIS  Capillaryloops (endothelial tubes) develop in some of these ridges and provide nourishment for the epidermis.  Sensory nerve endings form in others;  Thedeveloping afferent nerve fibers apparently play an important role in dermatomal pattern of innervations of the skin. 21 SKIN GLANDS -Sebaceous Glands -Sweat Glands 22  SEBACEOUS GLANDS  Mostsebaceous glands develop as buds from the sides of developing epithelial root sheaths of hair follicles 23  SEBACEOUS GLANDS  The buds grow into the surrounding connective tissue and branch to form the primordia of several alveoli and their associated ducts  The central cells of the alveoli break down, forming an oily secretion-sebum-  Sebum is released into the hair follicle and passes to the surface of the skin, ◦ where it mixes with desquamated peridermal * cells to form vernix caseosa (check slide 4) 24  SEBACEOUS GLANDS  Sebaceous glands where there are no hair follicles (e.g., in the glans penis and labia minora) develop in a similar manner to buds from the epidermis. 25  SWEAT GLANDS  There are 3 main types: ◦Eccrine sweat glands: are located in the skin throughout most of the body ◦Apocrine sweat glands: in humans is mostly confined to the axilla, pubic, and perineal regions and areolae of the nipples ◦Mammary glands: are a modified and highly specialized type of sweat glands 26  Eccrine -SWEAT GLANDS  They develop as epidermal downgrowths (cellular buds) into the underlying mesenchyme 27  Eccrine -SWEAT GLANDS  As the buds elongate, their ends coil to form the primordium of the secretory part of the gland Approx. 20wks 28  Eccrine -SWEAT GLANDS  The central cells of the primordial ducts degenerate, forming a lumen.  The peripheral cells of the secretory part of the gland differentiate into myoepithelial and secretory cells  The myoepithelial cells are thought to be specialized smooth muscle cells that assist in expelling sweat from the glands.  Eccrine sweat glands begin to function shortly after birth 29  Apocrine-SWEAT GLANDS  They develop from downgrowths of the stratum germinativum of the epidermis that give rise to hair follicles.  As a result, the ducts of these glands open, not onto the skin surface as do eccrine sweat glands, but into the upper part of hair follicles superficial to the openings of the sebaceous glands.  They begin to secrete during puberty. 30  Mammary-SWEAT GLANDS  Mammary buds begin to develop during the sixth week as solid downgrowths of the epidermis into the underlying mesenchyme  The buds develop from the Mammary Crest  Which are thickened strips of ectoderm extending from the axillary to the inguinal regions) READ 31  APPENDAGES  Toenails and fingernails begin to develop at the tips of the digits at approximately 10 weeks  Development of fingernails precedes that of toenails by approximately 4 weeks  The primordia of nails appear as thickened areas or nail fields of epidermis at the tip of each digit.  Later these nail fields migrate onto the dorsal surface, carrying their innervations from the ventral surface.  The nail fields are surrounded laterally and proximally by folds of epidermis, the nail folds READ 32  APPENDAGES  Teeth develop from ectoderm, mesoderm, and neural crest cells. ◦The enamel is produced by ameloblasts, which are derived from the oral ectoderm; ◦All other dental tissues develop from mesenchyme, derived from mesoderm and neural crest cells 33  CONGENITAL ANOMALIES  Ichthyosis (Gr. ichthys, fish): ◦ skin disorders resulting from excessive keratinization  The skin is characterized by dryness and fishskin- like scaling, which may involve the entire body surface 34  SOME CONGENITAL ANOMALIES  Albinism: In generalized albinism, an autosomal recessive trait, the skin, hairs, and retina lack pigment; ◦ however, the iris usually shows some pigmentation. ◦ Albinism occurs when the melanocytes fail to produce melanin because of the lack of the enzyme tyrosinase 35  SOME CONGENITAL ANOMALIES  Hypertrichosis: ◦ Excessive hairiness results from the development of supernumerary hair follicles 36  SOME CONGENITAL ANOMALIES  Absence of Skin: In rare cases, small areas of skin fail to form, giving the appearance of ulcers. The area usually heals by scarring unless a skin graft is performed. Absence of patches of skin is most common in the scalp  Gynecomastia  Absence of Nipples (Athelia) or Breasts (Amastia)  Aplasia of Breast  Supernumerary Breasts and Nipples 37 SOME CONGENITAL ANOMALIES 38  SOME CONGENITAL ANOMALIES  Inverted Nipples: Sometimes the nipples fail to elevate above the skin surface after birth, that is, they remain in their prenatal location  Alopecia (Loss of Hair / Baldness)  Congenital Anonychia :Absence of nails at birth is extremely rare.  Anonychia results from failure of nail fields to form or from failure of the proximal nail folds to form nail plates.  The abnormality is permanent 39  SOME CONGENITAL ANOMALIES  Congenital Ectodermal Dysplasia: ◦This condition represents a group of rare hereditary disorders involving tissues that are ectodermal in origin. ◦The teeth are completely or partially absent. Often the hairs, nails, and skin are also severely affected 40  SOME CONGENITAL ANOMALIES  Ectrodactyly-Ectodermal Dysplasia- Clefting Syndrome ◦is a congenital skin condition that is inherited as an autosomal dominant trait. ◦involves both ectodermal and mesodermal tissues, consisting of ectodermal dysplasia associated with hypopigmentation of skin and hair, scanty hair and eyebrows, absence of eyelashes, nail dystrophy, hypodontia and microdontia, ectrodactyly, and cleft lip and palate. 41  SOME CONGENITAL ANOMALIES  Pili Torti: ◦the hairs are twisted and bent  Congenital Anonychia: ◦ Absence of nails at birth is extremely rare. Anonychia results from failure of nail fields to form or from failure of the proximal nail folds to form nail plates. The abnormality is permanent READ MORE ON OTHERS 42  OTHER FACTS  Tetracyclines are extensively incorporated into the enamel and dentine of developing teeth, producing brownish- yellow discoloration and hypoplasia of the enamel.  Theyshould not be prescribed for pregnant women or children younger than 8 years of age 43