2. The Integumentary System

3. Consists of skin & Consists of skin & Its derivatives: Its derivatives:  Sweat glands  Sebaceous glands  Arrector pili muscles  Nails  Hair  Mammary glands

4. Development of Skin Skin consists of two layers that are derived from two different germ layers Skin consists of two layers that are derived from two different germ layers Epidermis, superficial epithelial tissue derived from surface ectoderm Epidermis, superficial epithelial tissue derived from surface ectoderm Dermis, deeper layer of connective tissue derived from the mesoderm Dermis, deeper layer of connective tissue derived from the mesoderm

5. Epidermis In the 4-5th week, the skin of the embryo consists of simple cuboidal epithelium….the surface ectoderm In the 4-5th week, the skin of the embryo consists of simple cuboidal epithelium….the surface ectoderm By the 7th week, the surface ectodermal cells proliferate and form a layer of squamous epithelium, the periderm (epitichium) and a basal germinative layer. By the 7th week, the surface ectodermal cells proliferate and form a layer of squamous epithelium, the periderm (epitichium) and a basal germinative layer. During 1 st & 2 nd trimesters, epidermal growth occurs in stages, which result in an increase in epidermal thickness During 1 st & 2 nd trimesters, epidermal growth occurs in stages, which result in an increase in epidermal thickness

6. Periderm The peridermal cells continually undergo keratinization and desquamation and are replaced by cells arising from the basal layer The peridermal cells continually undergo keratinization and desquamation and are replaced by cells arising from the basal layer The exfoliated cells form part of the white greasy substance, the vernix caseosa, that covers the body of the fetus The exfoliated cells form part of the white greasy substance, the vernix caseosa, that covers the body of the fetus Replacement of peridermal cells continue untill about the 21 st week, thereafter the periderm disappears and the stratum corneum forms Replacement of peridermal cells continue untill about the 21 st week, thereafter the periderm disappears and the stratum corneum forms

7. Basal Germinative Layer This layer becomes the stratum germinativum of the epidermis This layer becomes the stratum germinativum of the epidermis It proliferates and the new cells are displaced into the layers superficial to it. It proliferates and the new cells are displaced into the layers superficial to it. By 11 th week, an intermediate layer, containing several cell layers, is interposed between the basal cells and the periderm. By 11 th week, an intermediate layer, containing several cell layers, is interposed between the basal cells and the periderm.

8. Basal Germinative Layer cont’d Proliferation of stratum germinativum also forms epidermal ridges which extend into the developing dermis. Proliferation of stratum germinativum also forms epidermal ridges which extend into the developing dermis. These ridges begin to appear in embryo of 10 weeks and are permenantly established by the 17 th week. These ridges begin to appear in embryo of 10 weeks and are permenantly established by the 17 th week. These ridges produce grooves on the surface of palms of the hand and soles of the feet including digits These ridges produce grooves on the surface of palms of the hand and soles of the feet including digits

9. Melanoblasts & Melanocytes During the early fetal period the epidermis is invaded by melanoblasts, cells of the neural crest origin. During the early fetal period the epidermis is invaded by melanoblasts, cells of the neural crest origin. Melanoblasts move to dermoepidermal junction and differentiate into melanocytes Melanoblasts move to dermoepidermal junction and differentiate into melanocytes The melanocytes have several long processes. The melanocytes have several long processes.

10. Melanoblasts & Melanocytes cont’d The cell bodies of melanocytes are confined to the basal layers of the epidermis, and their processes extend between the epidermal cells The cell bodies of melanocytes are confined to the basal layers of the epidermis, and their processes extend between the epidermal cells The melanocytes begin producing melanin before birth and distribute it to the epidermal cells The melanocytes begin producing melanin before birth and distribute it to the epidermal cells

11. At birth all layers of the adult epidermis are present At birth all layers of the adult epidermis are present

12. Dermis The dermis is derived from the mesenchyme underlying the surface ectoderm The dermis is derived from the mesenchyme underlying the surface ectoderm This mesenchyme is derived from the: This mesenchyme is derived from the: Somatic layer of the lateral mesoderm (most of it) Somatic layer of the lateral mesoderm (most of it) Dermatomes of the somites (some). Dermatomes of the somites (some). By 11 th week, the mesenchymal cells begin to produce collagenous and elastic connective tissue fibers By 11 th week, the mesenchymal cells begin to produce collagenous and elastic connective tissue fibers

13. Dermal Papillae As the epidermal ridges are formed, the dermis projects upward into the epidermis and forms the dermal papillae As the epidermal ridges are formed, the dermis projects upward into the epidermis and forms the dermal papillae Capillary loops and sensory nerve endings develop in these papillae Capillary loops and sensory nerve endings develop in these papillae DP

14. Hair Begin to develop during the 3rd month, but they do not become visible until the 20 th week Begin to develop during the 3rd month, but they do not become visible until the 20 th week Begins as an epidermal proliferation, the hair bud, into the underlying dermis. Begins as an epidermal proliferation, the hair bud, into the underlying dermis. The deepest part of the hair bud becomes cup- shaped, forming a hair bulb The deepest part of the hair bud becomes cup- shaped, forming a hair bulb The hair bulb gets invaginated by mesenchymal hair papilla The hair bulb gets invaginated by mesenchymal hair papilla

15. Hair cont’d The central epithelial cells of the hair bulb give rise to the shaft of the hair, that grows through the epidermis and protrudes above the surface of the skin The central epithelial cells of the hair bulb give rise to the shaft of the hair, that grows through the epidermis and protrudes above the surface of the skin The peripheral cells of the hair bulb form the epithelial root sheath. The peripheral cells of the hair bulb form the epithelial root sheath. The cells of the epithelial root sheath proliferate to form a sebaceous gland bud. The cells of the epithelial root sheath proliferate to form a sebaceous gland bud.

16. Hair cont’d Surrounding mesenchymal cells differentiate into dermal root sheath. Surrounding mesenchymal cells differentiate into dermal root sheath. The arrector pili muscle differentiates from the surrounding mesenchyme The arrector pili muscle differentiates from the surrounding mesenchyme Melanoblasts migrate into the hair bulb and differentiate into melanocytes Melanoblasts migrate into the hair bulb and differentiate into melanocytes

17. Hair cont’d Hairs are first recognizable in the region of eyebrows, upper lip and chin Hairs are first recognizable in the region of eyebrows, upper lip and chin The first set of hairs that appear are fine and colorless and are called ‘lanugo’ hair The first set of hairs that appear are fine and colorless and are called ‘lanugo’ hair Lanugo hair are replaced during the perinatal period by coarser hair Lanugo hair are replaced during the perinatal period by coarser hair

18. Sweat Glands Develop at about 20 weeks as solid growth of epidermal cells into the underlying dermis Develop at about 20 weeks as solid growth of epidermal cells into the underlying dermis Its terminal part coils and forms the body of the gland Its terminal part coils and forms the body of the gland The central cells degenerate to form the lumen of the gland The central cells degenerate to form the lumen of the gland The peripheral cells differentiate into secretory cells and contractile myoepithelial cells The peripheral cells differentiate into secretory cells and contractile myoepithelial cells

19. Vernix Caseosa Vernix caseosa, is the waxy or cheesy white substance found coating the skin of the newborn. Vernix caseosa, is the waxy or cheesy white substance found coating the skin of the newborn. The vernix is secreted by the sebaceous glands around the 20th week of gestation The vernix is secreted by the sebaceous glands around the 20th week of gestation It is composed of: It is composed of: Sebum (the secretion of the sebaceous glands) Sebum (the secretion of the sebaceous glands) Desquamated epithelial cells Desquamated epithelial cells Fetal hair (lanugo hair) Fetal hair (lanugo hair) It protects the baby's skin from dehydation and from constant exposure to the amniotic fluid. It protects the baby's skin from dehydation and from constant exposure to the amniotic fluid.

20. Nails Begin to develop at about 10th week of gestation, as thickened areas of the epidermis at the tips of the digits. Begin to develop at about 10th week of gestation, as thickened areas of the epidermis at the tips of the digits. Later, these nail fields extend to the dorsal surface and become surrounded by the nail folds. Later, these nail fields extend to the dorsal surface and become surrounded by the nail folds. Cells from the proximal nail fold grow over the nail field and form keratinized nail plate, the primordium of the nail. Cells from the proximal nail fold grow over the nail field and form keratinized nail plate, the primordium of the nail.

21. The Mammary Glands Begin to develop during the 6th week as thickened strips of the ectoderm (mammary ridges) that extend from the axillary to the inguinal regions. Begin to develop during the 6th week as thickened strips of the ectoderm (mammary ridges) that extend from the axillary to the inguinal regions. They regress in most locations except in the area of the pectoral muscle, where they proliferate. They regress in most locations except in the area of the pectoral muscle, where they proliferate.

22. The Mammary Glands cont’d The downgrowth of epithelial tissue continues to proliferate into 16 to 24 solid outbuddings which give rise to the lactiferous ducts. The downgrowth of epithelial tissue continues to proliferate into 16 to 24 solid outbuddings which give rise to the lactiferous ducts. Fibrous connective tissue and fat of the mammary gland develop from the surrounding mesenchyme. Fibrous connective tissue and fat of the mammary gland develop from the surrounding mesenchyme. The lactiferous ducts at first open into a small mammary pit. The lactiferous ducts at first open into a small mammary pit.

23. Postnatal Development  Newborn (nipple is inverted)  Child (nipple elevates to form the usual nipple)  Puberty (breast enlarges due to development of the mammary glands) & deposition of fat  Late puberty  Young adult  Pregnant female

24. Anomalies Gynecomastia Gynecomastia Polythelia Polythelia Inverted nipples Inverted nipples