Embryology of the Integumentary system “The making of “

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Alfred Ammoury Alfred Ammoury Division of Dermatology, St George Hospital Division of Dermatology, St George Hospital UMC UMC 1

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Alfred Ammoury Division of Dermatology, St George Hospital UMC. Embryology of the Integumentary system “The making of “. Layers of skin. Skin is a complex organ Horizontally stratified into 3 compartments -epidermis -dermis -subcutis (hypodermis) Vertically penetrated by appendages - PowerPoint PPT Presentation

Transcript of Embryology of the Integumentary system “The making of “

Page 1: Embryology of the  Integumentary  system “The making of “

Alfred AmmouryAlfred Ammoury

Division of Dermatology, St George Hospital Division of Dermatology, St George Hospital UMCUMC

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Skin is a complex organ

Horizontally stratified into 3 compartments-epidermis-dermis-subcutis (hypodermis)

Vertically penetrated by appendages-hair follicles-sebaceous glands-eccrine and apocrine sweat glands

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Bilaminar embryonic disc :

Epiblast and the

hypoblast

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Primitive streak – raised groove on the dorsal surface of the epiblast

Gastrulation – a process of invagination of epiblast cells

Endoderm – formed from migrating cells that replace the hypoblast

Mesoderm – formed between epiblast and endoderm

Ectoderm – formed from epiblast cells that stay on dorsal surface

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Skin layers are derived from 2 different germ layers:

Ectoderm (lateral to the neural plate): epidermis

Mesoderm: dermis

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Earliest skin study (4 week): single layered epidermis and a thin mesenchymal dermis.

Progressive development over the first 6 months: by the end of the second trimester, the skin is a stratified squamous epithelium.

Dermis lags behind epidermis in developemnt.

Dermal bulk increases post nataly and its maturation continues

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Day 20-30: skin of embryo starts to develop (organogenesis).

Day 60: most organ systems have formed (including the skin). Embryo enters fetal period of growth and differentiation.

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Gastrulation occurs during the third week after fertilization

Complex process of involution and cell redistribution resulting in the formation of the three primary embryonal germ layers:

Ectoderm, Mesoderm, endoderm

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Shortly after gastrulation, the ectoderm further subdivides into neuroectoderm and the presumptive epidermis that covers the embryo

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At this stage, the ectoderm (presumptive epidermis) that covers the embryo is made of basal cells and superficial periderm cells

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Form part of the vernix caseosa

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Form a pavement epithelium that blanket the developing epidermis.

Exfoliated peridermal cells and sebum form the Vernix caseosa , a white greasy substance that covers the fetal body, protects it from amniotic fluid contents and facilitates delivery.

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Hematopoiesis has switched from the extraembryonic yolk sac to the bone marrow. The classical division between embryonal and fetal development.

Epidermal stratification occurs: formation of an intermediate layer, highly proliferative cells that eventually evolve into a multi layer structure that will replace the periderm.

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Basal layer begins to elaborate proteins that will anchor them to the developing basal lamina.

Late fetal development reveals the further differenciation of keratinocytes in the epidermis: granular layer, stratum corneum that replaces the periderm at W21.

Stratum germninativum starts to extend downward growth (ridges) into the developing dermis.

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Melanocytes, Merkel cells and Langerhans cells can be detected by the end of the embryonic period.

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Neural crest derived

W8 neural crest cells mgrates into mesenchymal tissue and differentiate into melanoblasts.

Melanoblasts localize to DEJ and hair bulbs, and differenciates into melanocytes

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Bone marrow derived

Detectable by 40 days

By the third trmester most of the adult number of these cells will have been produced

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Slowly adapting touch receptors.

Controversial origin: neural crest Vs in situ differentiation of ectodermal cells.

Present at 11-12 weeks.

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Develops from mesenchyme

W11: mesenchymal cells produce collagenous and elastic tissue.

Part of the dermis project into the epidermis forming pappillae.

Capillary loops and nerves develop in these papillae

Major vasculature : by the end of the 1st trimester.

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Hair follicles, sebaceous glands and sweat glands develop from the epidermis and they grow into the dermis.

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W12: Hair first appears on eyebrow & upper lip

1st hair is lanugo hair (soft, fine, lightly pigmented and non mediullated).

Replaced by coarse terminal hair

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Stratum germinativum proliferates into the dermis.

Hair bud becomes club shaped=Hair bulb containing germinal matrix cells that willlatinize to form the hair shaft.

Hair bulbs are soon invaginated by small mesenchymal hair papilla.

Arrector pilorum develop from the surrounding mesenchyme.

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Buds from the sides of developing epithelial root sheath of hair follicles

Inactive until puberty.

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They develop as epidermal downgrowthInto the underlying dermis

Starts at about W20

Functional at birth

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Develop from downgrowths of the stratum germinativum that gives rise to hair follicle

Begin secretion around 7-10 years.

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Fingernails reach the edge at W32

Toenails reach the edge at W36

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Highly modified and highly specialized type of sweat glands (development similar to that of SG)

W6: downgrowths of epidermal ridges in the pectoral area

Primary duct forms many 2ndary ducts that in turn develop to form lactiferous duct (15-20 at term).

Epidermis at the site forms a shallow pit mammary pit where the nipple will develop.

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