Integumentary System Development

From Embryology
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Skin structure cartoon.jpg

Introduction

The integumentary system covers the surface of the embryo (skin) and its specialized skin structures including hair, nails, sweat glands, mammary glands and teeth. As a system it has contributions from all embryonic layers.

The skin provides a barrier between ourselves and our environment, it also contains specializations in different regions including hair, nails, glands and sensory receptors.

The two major tissue organizations of epithelial (ectoderm, epidermis) and mesenchyme (mesoderm connective tissue, dermis and hypodermis) are shown within skin. In addition, we have aslo extensive populating by melanocytes (neural crest) and sensory nerve endings.

It remains today as possibly the first epithelial specialization from which other epithelial specializations arose that are now located inside the body.

Ectoderm forms the surface epidermis and the associated glands. Mesoderm forms the underlying connective tissue of dermis and hypodermis. Neural crest cells also migrate into the forming epidermis and the skin is also populated by specialized sensory endings.


Integumentary Links: integumentary | Lecture | hair | tooth | nail | integumentary gland | mammary gland | vernix caseosa | melanocyte | touch | Eyelid | outer ear | Histology | integumentary abnormalities | Category:Integumentary
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Historic Embryology - Integumentary  
1906 Papillary ridges | 1910 Manual of Human Embryology | 1914 Integumentary | 1923 Head Subcutaneous Plexus | 1921 Text-Book of Embryology | 1924 Developmental Anatomy | 1941 Skin Sensory | Historic Disclaimer
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Some Recent Findings

  • The integumentary skeleton of tetrapods: origin, evolution, and development.[1] "Three types of tetrapod integumentary elements are recognized: (1) osteoderms, common to representatives of most major taxonomic lineages; (2) dermal scales, unique to gymnophionans; and (3) the lamina calcarea, an enigmatic tissue found only in some anurans."

Textbooks

  • Human Embryology (2nd ed.) Larson Chapter 14 p443-455
  • The Developing Human: Clinically Oriented Embryology (6th ed.) Moore and Persaud Chapter 20: P513-529
  • Before We Are Born (5th ed.) Moore and Persaud Chapter 21: P481-496
  • Essentials of Human Embryology Larson Chapter 14: P303-315
  • Human Embryology, Fitzgerald and Fitzgerald
  • Color Atlas of Clinical Embryology Moore Persaud and Shiota Chapter 15: p231-236

Objectives

  • Understand the differentiation of the epidermis and dermis.
  • Understand the formation of hair and nails.
  • Understand the formation of sweat glands, mammary glands.
  • Understand the formation of teeth.

Development Overview

Human Embryo (Week 8, Stage 22) Integument

Ectoderm and Mesoderm Origin

4 weeks

  • simple ectoderm epithelium over mesenchyme.

1-3 months

  • ectoderm- germinative (basal) cell repeated division of generates stratified epithelium.
  • mesoderm- differentiates into connective tissue and blood vessels.

4 months

Fetal integumentary histology 01.jpg

Fetal human integumentary histology[2]

  • Basal cell - proliferation generates folds in basement membrane.
  • Neural crest cells - melanoblasts migrate into epithelium. These are the future melanocyte pigment cell of the skin.
  • Embryonic connective tissue- differentiates into dermis, a loose ct layer over a dense ct layer. Beneath the dense ct layer is another loose ct layer that will form the subcutaneous layer.
  • Ectoderm contributes to nails, hair follictles and glands.
  • Nails form as thickening of ectoderm epidermis at the tips of fingers and toes. These form germinative cells of nail field.
  • Cords of these cells extend into mesoderm forming epithelial columns. These form hair follocles, sebaceous and sweat glands.

5 months

  • Hair growth initiated at base of cord, lateral outgrowths form associated sebaceous glands.
  • Other cords elongate and coil to form sweat glands.
  • Cords in mammary region branch as they elongate to form mammary glands. These glands will complete development in females at puberty. Functional maturity only occurs in late pregnancy.

Fetal Dermis

The following data is from an immunohistological study of fetal skin dermis layer.

  • Collagen type I is the principal component of extracellular matrix (ECM) (also in adult skin).
  • Collagen type III high ratio to collagen type I (than adult skin).
  • Glycosaminoglycans (GAGs) level higher (than adult skin).
  • Hyaluronic acid and chondroitin sulfate both higher.
  • Elastin was not present (found in adult skin).


Adult Epidermal Stem Cells

The following information is from a recent study on mouse skin using a single cell labelling system with longitudinal tracing and confocal imaging.[3]

Organization of the epidermis. Hair follicles contain stem cells located in the bulge (b, green), with the potential to generate lower hair follicle (lf), sebaceous gland (sg, orange) upper follicle (uf) and interfollicular epidermis (IFE, beige). The schematic shows the organization of keratinocytes in the IFE, as proposed by the stem/TA cell hypothesis. The basal layer comprises stem cells (S, blue), transit amplifying cells (TA, dark green), and post-mitotic basal cells (red), which migrate out of the basal layer as they differentiate (arrows).

Hair follicle development.jpg

Projected Z-stack confocal images of IFE wholemounts from AhcreERT R26EYFP/wt mice viewed from the basal surface at the times shown following induction. Yellow, EYFP; blue, DAPI nuclear stain. Scale bar, 20 microns.

Reprinted by permission from Macmillan Publishers Ltd: Nature. 2007 Mar 8;446(7132):185-9, copyright (2007)

Adult epidermal stem cells[3] "According to the current model of adult epidermal homeostasis, skin tissue is maintained by two discrete populations of progenitor cells. ...Here we show that clone-size distributions are consistent with a new model of homeostasis involving only one type of progenitor cell. These cells are found to undergo both symmetric and asymmetric division at rates that ensure epidermal homeostasis."

Links: MRC - Phil Jones Laboratory

Melanocytes

Melanoblast migration.png Mouse-melanoblast migration icon.jpg
Mouse melanocyte migration[4] Movie Mouse Skin - Melanoblast Migration E14.5[5] Quicktime | Flash

Keratin

Cytoskeleton intermediate filament protein of epithelial cells required for cell mechanical stability and integrity, humans have 54 functional keratin genes.

Intermediate Filaments Type I

Acidic keratins (pI < 5.7) 40–64 kDa (n = 28)

  • K9-28 (epithelia)
  • K31-40 (hair/nail)

Intermediate Filaments Type II

Basic keratins (pI ≥ 6.0) 53–67 kDa (n = 26)

  • K1-8, K71-80 (epithelia)
  • K81-86 (hair/nail)
  • Keratins form heterodimers that assemble into heteropolymeric keratin filaments

Elaine Fuchs

Elaine Fuchs

A key researcher in the understanding of skin and keratin development Elaine Fuchs: A love for science that's more than skin deep. Interviewed by Ben Short[6] "Elaine Fuchs has collected many awards in her 30 years researching mammalian skin development, but it's hard to beat the two prizes she received in late 2009. Shortly before winning the prestigious L'Oreál-UNESCO award for women in science, Fuchs was awarded the National Medal of Science—the US's highest honor for outstanding scientific contributions."

Links: Lecture Cytoskeleton - Intermediate Filaments

References

  1. <pubmed>19422424</pubmed>
  2. <pubmed>19701759</pubmed>| PMC2799629 | Arch Dermatol Res
  3. 3.0 3.1 <pubmed>17330052</pubmed>
  4. <pubmed>16277556</pubmed>| PLoS Biol.
  5. <pubmed>20067551</pubmed>| PMC2859249
  6. <pubmed>20038675</pubmed>| PMC2806278


Reviews

Articles

Search PubMed

Search April 2010 "Integumentary Development" - All (86) Review (9) Free Full Text (18)

Search Pubmed: Integumentary Development | Skin Development | Hair Development | Tooth Development

Additional Images

Category:Integumentary

Terms

  • dermomyotome - Early embryonic dorsolateral half of the somite that will later divide to form both the dermatome and myotome. The dermatome will contribute the dermis and hypodermis of the skin. The myotome will contribute the skeletal muscle of muscoloskeletal system. Development sequence: mesoderm to paraxial mesoderm to somite to "dermomyotome" then dermatome and myotome. (More? Somitogenesis | Musculoskeletal System Development | Integumentary System Development)
  • dermatome - The early embryonic dorsal portion of the somite that will contribute the dermis and hypodermis of the skin. Note in the adult, this term is used to the skin sensory region innervated by a single spinal (nerve) segment. mesoderm - paraxial mesoderm - somite - dermomyotome - dermatome - dermis. (More? Somitogenesis | Musculoskeletal System Development | Integumentary System Development | Neural System Development)
  • epidermis - Histological term describing the external cellular epithelial layer of the integumentary (skin) covering the entire body. This surface layer of keratinocytes is ectoderm in origin, while the underlying connective tissue layers of dermis and hypodermis are mesoderm in origin. (More? Integumentary Development)
  • merkel cell - An epidermal-derived cell in touch-sensitive area of the epidermis and mediate mechanotransduction in the skin. Previously thought to be neural crest in origin, but recently shown to arise from the embryonic epithelium. The cells are named after Friedrich Sigmund Merkel, a German anatomist who was the first to describe them in 1875. (More? Lecture - Integumentary Development | PMID19786578 | PMID3782861)
  • melanin - (Greek, melanos = black) The pigment produced by melanocytes that provides photoprotection, preventing cellular DNA damage, and colouring of the cells that secret and absorb the pigment.
  • melanoblast - (Greek, melanos = black) The neural crest precursor cell that differentiates to form melanocytes located in the skin and other tissues that produces melanin. (More? Neural Crest Development | Integumentary System Development)
  • melanocyte - (Greek, melanos = black) A pigmented cell, neural crest in origin, differentiating from melanoblasts located in the skin and other tissues that produces melanin. The melanocytes within the integument (skin) transfer melanin to keratinocytes to give skin colour and to the hair follicle to give hair colour. Melanocytes are also located within "non-cutaneous" tissues in the eye (for eye colour), harderian gland and inner ear. This is the cell type that proliferates in the cancer melanoma. (More? Neural Crest Development | Integumentary System Development)


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Cite this page: Hill, M.A. (2024, March 28) Embryology Integumentary System Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Integumentary_System_Development

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© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G