{{ANAT2341Project2014header}}
=Integumentary=
==Introduction==
This page concerns the development of the integumentary system in the fetal stage of development, particularly its organs i.e. the skin, glands, hair, teeth, and nails. It explores the mechanism of development as well as the timeline of development. This page also outlines some recent findings on the development of the integumentary system, as well as historic findings. Finally, this page also explores some of the congenital abnormalities of the integumentary system, its mechanism or pathogenesis, clinical manifestations, and how they are treated or managed.

==Development Overview==
===Skin===

The skin consists of 2 layers: the outer layer (epidermis) and a deeper connective tissue layer (dermis).
*The epidermis is derived from the ectoderm. Initially it exists as only a single layer of ectodermal cells at 7-8 days of gestation. However, by about 13-14 weeks after gestation, a 3- layered structure of fetal epidermis exists- consisting of the stratum basale, 1 or 2 intermediate layers and the periderm. The peridermal cells eventually become desquamated and form part of the vernix cervix.
** The 5 definitive layers of the adult skin are evident in the human fetus after 22-24 weeks of gestation. Indirect influences form the dermis help differentiate the epidermis into: stratum basale, stratum spinosium, stratum granulosum, stratum lucidum and stratum corneum.
*The somatic mesoderm is the embryonic origin of the dermis. The mesoderm of the dermatones of the body, also contribute to the development of the dermis. Specifically though, in the head and neck region of the body, the dermis is derived from neural crest cells.
** The dermis is initially composed of just mesenchymal cells- loosely aggregated mesodermal cells. These mesenchymal cells later develop into fibroblasts- which function to secrete collagen and lay-down elastic fibers into the extracellular matrix.

3 other specialised cells of the epidermis also exists- these include melanoblasts, Langherhan cells and Merkel cells.
*Melanoblasts- are derived from neural crest cells that have migrated into the stratum basale. Mid-pregnancy, melanosomes are observed, differentiating the melanoblasts into melanocytes
*Langheran cells- are derived from bone marrow (originally form mesoderm) and migrate into the epidermis. They have the function of antigen presentation.
*Merkel cells- still have an uncertain origin. They have a function related to mechanoreception.

{| style="width:60%; height:125px" border="1" align="center"
|-
! Week !! Description !! Phase Diagram
|-
| Week 6-8|| In an electron micrograph study of the epidermis, the periderm and and basal layer of the developing skin was observed. || [[Image:Human_embryo_skin_8-9_week_EGA.jpg|100x100px|Weeks 6-8]]
|-
| Week 7-9 || In an electron micrograph study of the epidermis at weeks 7-9 of development, the stratified three-layer structure of the epidermis was observed. Kertain filaments have been encircled. || [[Image:Human_embryo_skin_9-11_week_EGA.jpg|100x100px| Weeks 7-9]]
|-
| Week 14 || By week 14, the basal layer, the intermediate layer/s and the periderm 3-layered structure can be observed in the fetus. By week 14, K17 can also be found in the basal and intermediate layers of the epidermis (In adult skin, K17 was not observed) || [[Image:Fetal_integumentary_histology_14w.jpg|100x100px| Week 14]]
|-
| Week 16 || In a study, by week 16, developing blood vessels were observed. CD31 and a sub-type of smooth-muscle actin stained positive in these observed developing blood vessels. || [[Image:Inaugumentary_week16.jpg|100x100px| Week 16]]
|-
| Week 18 || Example || [[Image:542px-Fetal_integumentary_histology_18.jpg|100x100px| Week 18]]
|-
| Week 19 || In a study, by week 19, as opposed to week 14, K17 was found present in the basal, intermediate and periderm layers. K17 also stained positive in the developing hair follicles. || [[Image:Inaugumentary-_Week_19.jpg|100x100px| Week 19]]
|-
| Week 20 || By week 20, hair follicles can be already be seen in the epidermis. The total number of intermediate layers has also increased || [[Image:Fetal_integumentary_histology_20.jpg|100x100px|Week 20]]
|-
| Week 22 || In an electron micrograph study at week 22 of development, kertanised epidermis was analysed. It was observed that glycogen was abundantly present throughout all epidermal layers. The included arrows, highlight the keratin filament bundles, which are now organised and peripherally placed. || [[Image:Human_embryo_skin_24_week_EGA.jpg|100x100px| Week 22]]
|-
| Adult|| In adult skin- a greater diversity of cells can be seen as more cells differentiate. Basal, spinous, granular and cornified cells are all example of such. In another study, chondroitin sulphate was observed in the basement membrane zone of the adult epidermis. In the same study, chondroitin sulphate was only observed towards the upper-part of the dermis. Also, elastin was present in the adult specimens, but not in the earlier fetal samples. || [[Image:Fetal_integumentary_histology_Adult.jpg|100x100px| Adult]] [[Image:542px-Fetal_integumentary_histology_Adult.jpg|100x100px| Adult]]
|}

<pubmed>19701759</pubmed>
<pubmed>PMC2113922</pubmed>

===Glands===
{| align="center" style="width:70%; height:200px" border=1
|-
! Gland Type !! Description
|-
| Sebaceous Glands|| *Sebaceous glands develop from the epithelial wall of the hair follicle.
*Vernix caseosa
Vernix caseosa is a material produced by sebaceous glands in the foetus in the last trimester of development <ref name="PMID15830002"><pubmed>15830002</pubmed></ref> and is characterised by it’s cheese-like appearance around the neonate at birth. The functions of vernix caseosa include:
*thermal regulation <ref name="PMID15830002"><pubmed>15830002</pubmed></ref>
*barrier to water loss (to keep fetal skin hydrated)<ref name="PMID21504444"><pubmed>21504444</pubmed></ref><ref name="PMID15830002"><pubmed>15830002</pubmed></ref>
*acid mantle development <ref name="PMID15830002"><pubmed>15830002</pubmed></ref>
*prevents the epidermis from water contact while epidermal cornification and formation of the stratum corneum occurs<ref name="PMID21504444"><pubmed>21504444</pubmed></ref>
|-
| Mammary Glands || *Mammary glands develop from the mammary ridge- a downgrowth of the epidermis (ectoderm) into the underlying dermis (mesoderm). This occurs at about week 6 of development. Prior to puberty, the mammary glands are anatomically indistinguishable.
|-
| Sweat Glands || *Eccrine and apocrine sweat glands develop from the downgrowths of the epidermis into the underlying dermis. It has been seen and detected in studies from week 21.
|}

{| style="width:40%; height:170px" align="center"
|-
| [[Image:Integumentary_histology_02.jpg|frame| 250x250px|Histology of eccrine sweat gland]] || [[Image:Integumentary-_sebaceous_gland_histology_01.jpg|frame|centre|250x250px|Histology of sebaceous gland]]
|}

::: Cite this page: Hill, M.A. (2014) Embryology Integumentary System - Gland Development. Retrieved October 7, 2014, from https://php.med.unsw.edu.au/embryology/index.php?title=Integumentary_System_-_Gland_Development
<references/>

===Hair===
[[Image:Hair_development_stages.jpg|frame|right|middle|300x250px|The stages of hair development]]

Hair originates from the ectoderm. At about 12 weeks, it is believed that specific signals from the dermis begin to induce hair follicle formation <ref name= PMID1566372><pubmed>1566372</pubmed></ref><ref name= PMID20590427><pubmed>20590427</pubmed></ref>. Through reciprocal interactions, cells from the stratum basale grow into the underlying dermis. The epithelial cells influenced by these dermal signals, develop a placode- a thickening of the columnar cells. Signalling from the placode than leads to the development of a dermal condensate, which further induces the downward growth of the placode. The hair follicle, continues to proliferate and enclose the dermal condensate, forming a deep, club-shaped hair bud, with an invaginated dermal papillae <ref name= PMID11841536><pubmed>11841536</pubmed></ref>. These dermal papillae are rapidly infiltrated by blood vessels and nerve endings. The epithelial cells within the hair bulb, then begin to differentiate into the germinal matrix – which grow, proliferate and keratinise to form the hair shaft and internal root sheet<ref name= PMID11841536><pubmed>11841536</pubmed></ref>. Other epithelial cells outside of the hair bud, form the external hair sheeth. Mesodermal cells of the dermis that surround the invaginating hair follicle form the dermal root sheeth and the arrecrtor pili muscles for hairs.

===Nail===
Together, fingernails and toenails are modifications of the epidermis, embryologically derived in humans from the same origin of ectodermal skin cells.
* Nails commence development at the tips of the digits around the stage of 10 weeks, with the initiation of fingernail growth preceding that of toenails by approximately 4 weeks. The earliest recognisable stages of nail development by week 10 are thickenings of epidermis, known as the primary nail fields, repositioning from the initial ventral surface to the eventual dorsum of each digit.
* The nail fields are bounded by folds of epidermis: the shallower lateral nailfolds, which adjoin into the much deeper proximal nailfold.
* The true nail is developed via the keratinization of cells within the proximal nailfold that proliferate over nail field, developing into the nail plate.
*Initially the developing nail is covered by a thin layer of epidermis, the eponychium (corneal layer of epidermis) that at later fetal stages declines to expose the free nail, however endures as the cuticle. Beneath the free end of the nail, epidermal cells aggregate to form the mass known as the hyponychium.
* By 32 and 36 weeks of development, the fingernails and toenails respectively reach the tips of the digits and toes.

:::Cite this page: Hill, M.A. (2014) Embryology Integumentary System - Nail Development. Retrieved October 7, 2014, from https://php.med.unsw.edu.au/embryology/index.php?title=Integumentary_System_-_Nail_Development

- need to reference this website: http://discovery.lifemapsc.com/library/review-of-medical-embryology/chapter-75-development-of-the-nails + textbook info here

{| class="wikitable"
|-
! Header text !! Header text
|-
| Week 9 || The primitive nail beings to from
|-
| Week 10|| The primary nail field is establish
|-
| Week 11 || Distal ridges of nail bed keratinise.
|-
| Week 13 || Early nail matrix.
|-
| Week 20 || Nail plate begins to grow over the nail bed.
|-
| Week 24 || Free nail plate is visible to the naked eye.
|}

===Teeth===

The ectoderm and the associated underlying layer of neural crest cells, are the origin for teeth development. As the oral epithelium grows and proliferates, it has a downward movement into the underlying neural crest layer. This leads to the formation of the dental lamina. These dental lamina, then, gives rise to tooth buds. These tooth buds, later form and develop into enamel organs. With further development, these enamel organs give rise to ameloblasts- which produce enamel. The dental papilla, on the other hand is formed by the neural crest cells which underlie the enamel organs <pubmed>19266065</pubmed></ref><ref name= PMID19266065>. These dental papillae than give rise to the dental pulp and odontoblasts- which produce predentin and dentin, in the adult body.

[[Image:Tooth development stage.jpg|frame|left|middle|425x300px|The stages of embryonic teeth development]]

{| class="wikitable"
|-
! Stage!! Week !! Description
|-
| (A) Lamina|| Week 6 || The oral ectoderm, closely interacts with the neural crest ectomesenchyme. In the Lamina stage, teeth may grow only within the epithelium.
|-
| (B) Placode|| Week 7 || The dental lamina and and the dental placodes arise, due to specific signals from adjacent epithelial cells
|-
| (C) Bud || Week 8 || Tooth buds are formed, as the epithelium cells interact with the messenchyme. This occurs at the sides of the dental placodes. Also, as opposed to the earlier Lamina stage, in the Bud stage, teeth may now only grow within the ectomesenchyme
|-
| (D) Cap|| Week 11 || After folding, the bud takes upon the shape of an inverted cap
|-
| (E) Bell|| Week 14 || The bud refolds once again, this time taking upon the shape of a bell
|}

<html5media height="300" width="400">https://www.youtube.com/watch?v=nRH8M-arC58</html5media>

===References===
<references/>
<pubmed>19266065</pubmed>| [http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=2651620&tool=pmcentrez PMCID: PMC2651620]

Int J Biol Sci. 2009; 5(3): 226–243.
Published online 2009 February 24.

Copyright © Ivyspring International Publisher. This is an open-access article distributed under the terms of the Creative Commons License (http://creativecommons.org/licenses/by-nc-nd/3.0/). Reproduction is permitted for personal, noncommercial use, provided that the article is in whole, unmodified, and properly cited.

==Some Recent Findings==
{|
|-bgcolor="F5FFFA"
|
* '''Expression of caspase-14 and keratin-19 in the human epidermis and appendages during fetal skin development:''' In recognition of the vital roles of CASP-14 and CK-19 in human skin development and maturation, the purpose of this study was to primordially investigate the expression of these two molecular factors throughout the stages of human fetal skin development from gestation to the postnatal period in order to evaluate their singular and collective functions in epidermal and associated appendage maturation and processes of differentiation and re-modelling of human fetal skin. The results of the immunohistochemical study showed the expression of CASP-14 to be a biochemical marker of human epithelial differentiation during gestation, whilst CK-19 was a marker for epidermal stem cells nests of the stratum basale of the fetal epidermis and appendages. CASP-14 was concentrated within the more differentiated fetal epidermal layers, progressively declining from the basal layer toward term whilst CK-19 showed reduced expression with progressive epidermal development of the fetal stages and was a biochemical marker for epidermal stem cells nests of the stratum basale showing marginal conservation in basal cell nests at term and postnatally. Expression of CASP-14 within the epidermal appendages of the hair follicles and sebaceous glands were concentrated within the greater differentiated inner root sheath whilst CK-19 was greatly concentrated within the outer root sheath. Inconsistent patterns of expression of both molecules CASP-14 and CK-19 were demonstrated within eccrine sweat glands. <ref name=PMID23377137><pubmed>23377137</pubmed></ref>
|}

{|
|-bgcolor="F5FFFA"
|
* '''Cxcr4 is transiently expressed in both epithelial and mesenchymal compartments of nascent hair follicles but is not required for follicle formation:''' Cellular signalling between mesencyhmal and epithelial layers of the developing skin initiate an assortment of morphogenetic events throughout embryogenesis, involving the formation of the skin and in particular, the development of hair follicles (HF). The aims of this study was to identify the specific signalling pathways associated with HF morphogenesis during the primary stages of mouse hair follicle development through the investigation of the precise expression patterns and role of the Cxcr4 receptor in two specialised cell types- mesenchymal dermal condensate (DC) cells and epithelial placode cells. Staining patterns of the Cxcr4 receptor in the budding HF revealed a high concentration within epithelial placode cells and later DC cells in developing HF’s, signifying a shift of expression between epithelial and mesenchymal layers during HF morphogenesis. The functionality of the Cxcr4 receptor was tested through Cxcr4 receptor ablation in both the mesenchymal and epithelial layers of the developing embryonic skin of conditional knockout mice (cKO) and was verified through immunofluorescence staining techniques. Normal HF development was still induced despite the absence of Cxcr4 expression in the skin of the cKO mice and numbers were comparable to those found in the wild-type (WT) control group in embryonic and postnatal skin groups demonstrating that the chemokine signalling through the Cxcr4 receptor is inessential for normal early HF development (Figure 1). <ref name= PMID25066162><pubmed>25066162</pubmed></ref>
|}

{| style="width:40%; height:170px" align="center"
|-
| [[Image: Eosin_staining_of_mouse_embryonic_skin.png|frame|250x250px|Figure 1: Hematoxylin/ eosin staining of embryonic skin sections and macroscopic view of external hair shafts of mouse. Cxcr4 receptor ablation in condensates and placodes show no effect on mouse HF morphogenesis. Hair follicle and shaft develop normally and in comparable numbers in both Tbx18cre (a) and Krt14-cre (b) Cxcr4fl/fl cKO mice.]] || [[Image: Screen Shot 2014-10-19 at 11.09.42 PM.png|frame|right|middle|300px|Figure 2: The expression of stem cell marker, nestin and proliferative marker, Ki67 in the developing human nail.]]
|}

{|
|-bgcolor="F5FFFA"
|
* '''The ventral proximal nail fold: stem cell niche of the nail and equivalent to the follicular bulge--a study on developing human skin:''' In comparison to the characterization of the stem cell niche within the folliculosebaceous-apocrine unit, the local microenvironment of stem cells within the human nail organ is yet to be characterized. The aims of the current study was through immunohistochemical analysis to describe the expression pattern of six follicular stem cell markers; cytokeratin 15 (CK15, two clones), cytokeratin 19 (CK-19), PHLDA1, CD200 and nestin within the developing human nail and compare it with the embryonic and fetal human hair follicle. In addition, locations of vast proliferative activity within the nail were assessed using labeling with Ki-67. The stem cell markers CK15 (both clones), CK19, PHLDA1, CD200 and nestin showed no staining within the nail and hair matrix samples, however were present within the central proximal nail fold and follicular bulge. The biochemical marker for proliferation, Ki-67 showed the highest concentration of proliferative cells within the hair germ, lower regions of the hair peg and in the hair matrix. In the developing human nail the expression of Ki-67 was most prominent within the nail bed epithelium and the later nail matrix. In contrast the lowest numbers of kI-67 positive staining cells were located in regions of stem cell niches of the follicular bulge and proximal ventral nail fold as stem cells divide infrequently (Figure 2). Throughout the course of embryonic development these stem cell markers exhibit a highly specific expression pattern both within the nail and the hair follicle. The results seem to suggest that during embryonic envelopment the proximal ventral nail fold is the niche for nail stem cells. <ref name= PMID22804461><pubmed>22804461</pubmed></ref>
|}

{|
|-bgcolor="F5FFFA"
|
* '''Msx1 and Tbx2 antagonistically regulate Bmp4 expression during the bud to cap stage transition in tooth development:''' The expression of Bmp4 is essential for the bud to cap phase transition in embryonic dental development and is accordingly firmly regulated, with earlier stages of expression localised within the dental epithelial placode developing in to a later forms of expression in the dental mesenchyme. Numerous transcription factors including Pax 9, Osr2, Barx 1, Msx1, have been identified to prompt and maintain Bmp4 expression in these critical stages of tooth development. In particular Msx1 is one such transcription factor induced through epithelial Bmp4 expression and in turn is essential for the induction and regulation of dental mesencyhmal Bmp4 expression. The results of this investigation have demonstrated the expression of an additional transcription factor, Tbx2, induced through epithelial Bmp4, within the dental mesenchyme at bud stage of dental development. To determine a functional connection between the Msx1 and Tbx2 transcription factors, a cross was made between Tbx2 and Msx1 mutant mice. The data demonstrates that bud phase tooth arrest in Msx1-/- mice is moderately restored in Msx1-/-. Tbx2+/- compound mutants. The maintenance of Tbx2 expression in the Msx-/- arrested tooth buds exhibits that the expression of Tbx2 is not dependant on that of Msx1. This restoration in the developmental process is associated with the establishment of the enamel knot (EK) and the reinstatement of mesencyhmal Bmp4 expression. Knockout of Tbx2 resulted in an increase mesencyhmal Bmp4 expression. This data demonstrates that subsequent to the induction of epithelial Bmp4, both transcription factors Msx1 and Tbx2 in turn antagonistically regulate odontogenic activity that results in EK formation as well as mesenchymal Bmp4 expression at the vital bud to cap phase transition in embryonic dental development resulting in appropriate morphogenesis and patterning. <ref name= PMID23720046><pubmed>23720046</pubmed></ref>

|}

{| class="wikitable mw-collapsible mw-collapsed"
! More Recent Papers
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|
<pubmed>23826487</pubmed>
<pubmed>22342389</pubmed>
<pubmed>24911066</pubmed>
<pubmed>25143675</pubmed>
<pubmed>23271751</pubmed>
<pubmed>25249463</pubmed>
<pubmed>23097355</pubmed>
<references/>
|}

==Historic Findings==

Knowledge of the Integumentary expands in conjunction with technological developments that allow observation of microscopic structures. Historically animal models have been used to map the stages in the development of the fetal integumentary system.

===Skin===

In 1900 Bardeen C. R used the pig animal model to study the histogenesis of the dermomyotomes and nervous appratus. Bardeen and other scientists established that the human skin results from the union of the epithelial material derived from the ectoderm (epidermis) and the connective tissue origination from the mesoderm (dermis).

http://journals.lww.com/plasreconsurg/Citation/1949/07000/CLINICAL_ASPECTS_OF_EMBRYOLOGICAL_SKIN.8.aspx
Bardeen, C. R. (1900). The development of the musculature of the body wall in the pig, including its histogenesis and its relations to the myotomes and to the skeletal and nervous apparatus. Johns Hopkins Hosp. Rep, 9, 367-399.

===Glands===

Sebacious glands / Sweat glands / Mamailliary

In the 1968 Robins and Breathnatch investigated the development on the sebacious and apocrine swelling in the skin, which where closely associated with development of the hair follicle. They observed differentiation of desmosomes and development of cytoplasmic contents of the cell.

===Hair===

he major anatomic details of hair development in the human foetus have been established by studies with light microscopy. Electron microscopy was not commonly used to until recently and so little was known about the ultrastructure of the skin. Over the past few years, reports have been published on the epidermal melanocytes and periderm.

* '''1958''' - Pinkus established the following stages of fetal hair follicle development: pre-germ, hair-germ, hair-peg,andbulbous-peg stages. Pinkus also determined that the developed hair fibres grow through the epidermis and appears at the level of the skin at around 19-21 weeks of development. The lanugo (foetal) hair is extremely fine with no medulla and a tip free of pigment.

* '''1968''' - Breathnach and Smith determined the fine structure of the cells of follicle and dermal papilla in the first two weeks of fetal development. The Peripheral Nerves, the sweat duct and nail development were also explored and the interrelationship of cells at particular foetal stages was deduced. These studies, and other laboratory animals, have provided information on the differentiation of cells and tissue of some functional importance and underline the role of cells and tissues.

Robertson, J. R. (Ed.). (2002). Forensic examination of hair. CRC Press.

* '''1959''' - Chase and Eaton's investigated fetal hair follicle development. With key observations in understanding the cycling nature of hair follicle growth, following development. Development begins with the downwards growth of the follicle structure from the level of the dermis. The follicle is a processes during the quiecent phase thought he adipose layer during gowth and differntiation. They also established that upward movement of hair inovlves the addition of next cells from the matrix of the follicle and an enlargement of each cell. Furthermore their research also showed that the epidermal and dermal layers were dynamic and interacting with each other. The most significant developments in the understanding of hair follicle development came from studies investigating the differentiation pattern of cells as the follicle develops. <ref name= PMID5656140><pubmed>5656140</pubmed></ref>

<pubmed>5656140</pubmed>
<pubmed>4097391</pubmed>

Determined that the hair fibre finally breaks through the epidermis and appres about the skin at around 19-21 weeks of development. The lanugo (foetal) hair is extremely fine with no medulla and a tip free of pigment.

===Nail===

Microscopy and staining techniques have been essential tools in study on developmental anatomy and physiology of the nail. Thus as technology advances scientists have been able to uncover the morphological changes during nail development. A review of the history allows us to recognise the major contributor to study of this field. History also reveals the interesting debate on the origins of keratinised cells which migrate to form the nail palate in weeks 20-24 of fetal development.

[[Image:Nail Plate Development - Pinkus .jpg|frame|right|middle|180x150px|Nail Plate Development - Pinkus|]]

* '''1883''' - Unna published a chapter on the anatomy and development of the human nail in the German textbook "Ziemsssen's Handbuch der Speciell Pathologie und Therapie" - Ziemsssen 's manual of special pathology and therapy.
* '''1927''' - Pinkus conducted his earliest investigations into fetal nail development. His findings were published in the "Handbuch Der Haut und Geschlechtskrankeiten” - Manual of Skin and Venerail Disease.
German scientists Unna and Pinkus contributed to the understanding of the anatomy. Both scientists proposed that the structures known as the nail matrix gave rise to the entire nail plate.

[[Image:Nail Plate Development -Lewis .jpg|frame|right|middle|160x135px|Nail Plate Development -Lewis|]]

* '''1954''' - Barton and Lewis conducted a through investigation on the microscopic features of the foetal and mature nail and surrounding soft tissue. Lewis challenged the current thought and proposed a tri-partite origin of the nail plate from three germinative tissues (1) the proximal nail fold (2) the matrix and (3) bed.
Prior to the 1900’s it was difficulty in obtaining normal foetal specimens. Furthermore, the histological staining techniques used to prepare slides of nail tissue often damage the specimen and little detail could be seen during the microscopic examinations. Barton and Lewis conducted this investigation in hopes that a better understanding of the normal developmental anatomy and physiology would assist physicians in diagnosing and treating abnormalities.

* '''1959''' - Samman carried out an investigation on the blood supply of the human toe nail. It was thought that a deeper understanding of morphology of the vasular supply might shed light on the genesis of the nail palate. Samman studied the morphology and distribution of blood vessels with in the nail found capillary loops through out the nail fold and concluded that this supports the theory of multiple sites giving rise to the nail plate.

* '''1963''' - Zaias conducted a number of studies on the embryology of the human nail. This investigation contributed to our understanding of different stages in foetal nail development. Zaias studied an number of foetal specimens at different stages in development. As a result, Zaias was able to propose a rough timeline highlighting morphological hallmarks in normal nail development.
* '''1968''' - Zaias and Alvazer investigated the formation of the primate nail plate. An autoradiographic study in the squirrel monkey.
The current understanding of fetal nail development is a summation contributions of many researches in the international scientific community. Today research continues, technology allows exploration beyond macroscopic and microscopic morphological changes in the fetal nail. Now the aim is to understand the molecular signalling with in the epidermal cells which drives this process.

<ref name= PMID13206419><pubmed>13206419</pubmed></ref> -- <pubmed>13206419</pubmed> -- Microscopic studies of fetal and mature nail and surrounding soft tissue. Lewis
<ref name= PMID14441224><pubmed>14441224</pubmed></ref> -- <pubmed>14441224</pubmed> -- The human toe nail. Its genesis and blood supply.
<ref name= PMID6161584><pubmed>6161584</pubmed></ref> -- <pubmed>6161584 </pubmed> -- Ultrastructure and Growth of Human Nails
<ref name= PMID14003041><pubmed>14003041</pubmed></ref> -- <pubmed>14003041</pubmed> -- Embryology of the Nail Zaias

===Teeth===
<ref name= PMID5267156><pubmed>5267156</pubmed></ref> -- <pubmed>5267156</pubmed>

==Abnormalities==

===Aplasia Cutis Congenita===
[[Image:Cutis aplasia.jpg|frame|right|middle|250x187px|Aplasia cutis congenita at the scalp]]
Aplasia cutis congenita (ACC) is a rare skin abnormality, characterised by the absence of all layers of the skin. It is most common to occur on the scalp (70%), specially the vertex. In severe cases, the defect can go as deep as the bone or the dura. Other sites of ACC include the skin of the limb regions. “ACC occurs in approximately 1 in 10000 live births, with a female-to-male ratio of 7:5.” The specific aetiologic agent for ACC is still unknown. It has been suggested to be genetic and/or environmental. The damage to the vertex is suggested to be the result of the biomechanical stretch at this area when the fetal brain is growing.<ref name= PMID22549580><pubmed>22549580</pubmed></ref>

Presently, ACC is managed via conservative treatments or surgical treatments. Conservative treatments refer to basic wound treatments and preventing infection with the use dressings and antibiotics. Surgical treatments, specifically scalp reconstruction procedures, aim to reconstruct the damage to the skin through skin grafts, local scalp flaps, and pericardial scalp flaps. Large defects are often treated using surgical treatments.<ref name= PMID23147310><pubmed>23147310</pubmed></ref>

===Dystrophic Epidermolysis Bullosa===
[[Image:Dystrophic Epidermolysis Bullosa lesions.jpg|frame|right|sub|270x230px|Severe skin lesions due to Dystrophic epidermolysis bullosa.<ref name="PMID23739692"><pubmed>23739692</pubmed></ref>]]
Dystrophic Epidermolysis Bullosa (DEB), a type of epidermolysis bullosa, is a genetic disease of the skin, usually present at birth or at an early age<ref name= PMID252845240><pubmed>25284524</pubmed></ref>. Currently, around 400,000 - 500,000 people are affected with the disease<ref name= PMID252845240><pubmed>25284524</pubmed></ref>. It is characterised by the fragility of the skin<ref name= PMID252845240><pubmed>25284524</pubmed></ref>, where it blisters upon minimal trauma and scars<ref name= PMID19945622><pubmed>19945622</pubmed></ref>, usually at the extremities<ref name= PMID252845240><pubmed>25284524</pubmed></ref>. It is caused by a mutation in collagen VII gene (COL7A1)<ref name= PMID19945622><pubmed>19945622</pubmed></ref><ref name= PMID24860657><pubmed>24860657</pubmed></ref>, which is responsible for the the formation of anchoring fibrils<ref name= PMID19945622><pubmed>19945622</pubmed></ref>. Anchoring fibrils are responsible for dermal-epidermal adherence<ref name= PMID19945622><pubmed>19945622</pubmed></ref>, that is why it’s loss of function results to blistering of the skin. In some cases, even teeth and nails are affected. Teeth of patients with DEB have enamel defects and when combined with poor oral hygiene, it may lead to decay. Nails of DEB patients are often dystrophic and will eventually be lost.<ref name= PMID252845240><pubmed>25284524</pubmed></ref>

There are currently no known cures for DEB; however there are techniques to manage the clinical manifestations of the disease, which include:
*wound care<ref name= PMID19945622><pubmed>19945622</pubmed></ref>
*preventing factors that may cause blistering<ref name= PMID19945622><pubmed>19945622</pubmed></ref>
*using aqueous disinfectants - highly effective<ref name= PMID19945622><pubmed>19945622</pubmed></ref>
*dental care<ref name= PMID252845240><pubmed>25284524</pubmed></ref>:
:-use of topical fluoride
:-careful prophylaxis
:-use of topical antibiotics to prevent secondary infections<ref name= PMID24860657><pubmed>24860657</pubme></ref>

One study is currently exploring the potential of protein therapy as a treatment for DEB. Their results show that intradermal injection of recombinant human collagen 7 in mice with DEB led to “restoration of C7 and anchoring fibrils.”<ref name= PMID19018253><pubmed>19018253</pubmed></ref> Other techniques that aim to restore C7 include:
*bone marrow transplant- improved blistering in mice specimen and increase survival rates<ref name= PMID24860657><pubmed>24860657</pubmed></ref>
*hematopoietic cell transplant (HCT)- increased deposition of C7 in injured skin<ref name= PMID24860657><pubmed>24860657</pubmed></ref>

===Congenital Alopecia Areata===
[[Image:Alopecia Areata.jpg|frame|right|middle|270x220px|Patches of hair loss: a sign of alopecia areata.<ref name="PMID23960401"><pubmed>23960401</pubmed></ref>]]
Alopecia areata (AA) is an abnormality of the hair affecting anagen hair follicles, characterised by well-demarcated patches of hair loss. It is non-scarring and can occur on the scalp and/or the body. 90% of AA cases occur on the scalp. 5%-10% of patients with AA lose all hair on their scalp; this is called alopecia totalis. While others lose all of their body hair, this is called alopecia universalis. <ref name= PMID17269961><pubmed>17269961</pubmed></ref> Its pathogenesis is considered to be both genetic and autoimmune. There is an abnormality with the genes related to the immune system and to the hair follicles. And histopathology shows signs of lymphatic infiltration of the hair follicles and the loss of these scalp lymphocytes allow hair follicles to recover.<ref name= PMID16338213><pubmed>16338213</pubmed></ref> High frequencies of catagen and telogen hair follicles are also present in areas affected by AA.<ref name= PMID17269961><pubmed>17269961</pubmed></ref>

There is currently no cure for AA. There are several treatments to combat AA but none of these have led to remission of the disease, the most effective being corticosteroids and topical immunotherapy.<ref name= PMID17269961><pubmed>17269961</pubmed></ref> A new method of treating alopecia areata is currently being studied. Transepidermal drug delivery (TED) is a new treatment that functions by creating micro-channels in the epidermis. By doing so, drug delivery to the skin is improved. This treatment was highly effective and had lower rates of side effects, e.g. pain, compared to previous treatments.<ref name= PMID25260052><pubmed>25260052</pubmed></ref>

===Harlequin Ichthyosis===
[[Image:Harlequin Ichthyosis.jpg|frame|right|middle|250x200px|A baby with harlequin ichthyosis.<ref name="PMID24520234"><pubmed>24520234</pubmed></ref>]]
Congenital ichthyosis is an autosomal recessive disease of the skin, characterised by visible and excessive scaling of the skin and hyperkeratosis, i.e. thickening of stratum corneum layer of the epidermis and in some cases, hypohidrosis, i.e. the lack of ability to sweat. <ref name= PMID19824737><pubmed>19824737</pubmed></ref> Harlequin ichthyosis (HI) occurs only in 1 in 1,000,000 babies. It is life-threatening in the first few weeks and/or months of the neonate.<ref name= PMID19824737><pubmed>19824737</pubmed></ref> The thick skin can restrict movement of the baby and sometimes constrict extremities and lead to necrosis then autoamputation.<ref name= PMID23419760><pubmed>23419760</pubmed></ref> Babies with HI are also characterised by bilateral ectropion (everted eyelids), eclabium (everted lips), and underdeveloped nose.<ref name= PMID23419760><pubmed>23419760</pubmed></ref> In 50% of HI cases, respiratory failure is often the cause of death.<ref name= PMID24124810><pubmed>24124810</pubmed></ref> This disease is caused by a nonsense mutation in the ATP-binding-cassette A12 (ABCA12) gene, which is responsible for encoding a lipid transporter essential for the regulation of lamellar bodies. <ref name= PMID19824737><pubmed>19824737</pubmed></ref><ref name= PMID23419760><pubmed>23419760</pubmed></ref><ref name= PMID24124810><pubmed>24124810</pubmed></ref>

There is currently no known cure for this disease. Management techniques include:
*Monitoring in neonatal intensive care units.
:-Temperature within the incubator is controlled to avoid fluctuation in body temperature and to stop sweating. <ref name= PMID19824737><pubmed>19824737</pubmed></ref>
*Mechanical removal of excess scales from the skin <ref name= PMID19824737><pubmed>19824737</pubmed></ref>
*Bathing to remove excess scales from the skin<ref name= PMID19824737><pubmed>19824737</pubmed></ref>
*Topical therapy - to reduce hyperkeratosis. <ref name= PMID19824737><pubmed>19824737</pubmed></ref><ref name= PMID24124810><pubmed>24124810</pubmed></ref>
*Use of oral retinoids - known to have high rates of survival.<ref name= PMID24124810><pubmed>24124810</pubmed></ref>

===Hypohidrotic Ectodermal Dysplasia===
[[Image:Oligodontia.jpg|frame|right|middle|250x187px|Oligodontia: a clinical manifestation of HED.<ref name="PMID21165248 "><pubmed>21165248 </pubmed></ref>]]
Hypohidrotic ectodermal dysplasia (HED) is the most of all ectodermal dysplasias, caused by an abnormality in the development of ectodermal tissues, which inlude skin, hair, teeth, sweat glands, and nails.<ref name= PMID20682465><pubmed>20682465</pubmed></ref><ref name= PMID24678015><pubmed>24678015</pubmed></ref> Patients with ectodermal dysplasia often have sparse hair and oligodontia, which is a condition where teeth are missing and are poorly developed.<ref name= PMID20682465><pubmed>20682465</pubmed></ref><ref name= PMID24678015><pubmed>24678015</pubmed></ref> Sweating is a very important function in the body in terms of thermoregulation. HED is mainly characterised by hypohidrosis due to the lack of sweat glands in the skin, which could lead to hyperpyrexia and sometimes death. In neonates, the mortality rate of HED reaches up to 30%, with the first year of life having the highest risk. <ref name= PMID20682465><pubmed>20682465</pubmed></ref> HED is caused by a genetic abnormality of the ectodysplasin A gene (EDA) and passed on by X-linked inheritance. The mutations of this gene results in the poor sweating ability or none at all in a person. The effects of this abnormality is usually more severe in males than in females. <ref name= PMID21357618><pubmed>21357618</pubmed></ref><ref name= PMID24678015><pubmed>24678015</pubmed></ref>

There is currently no pharmacological therapies for HED but there are methods applied to prevent the disease from aggravating. Neonates with HED are placed in incubators and monitored to prevent them from overheating. Management of this disease gets easier as the patient ages. Adults with HED can control their thermoregulation by staying in cool environments or drinking cold drinks to lower the body temperature. Currently, there are studies that aim to find a cure for this abnormality, e.g. gene replacement therapy in animal models.<ref name= PMID24678015><pubmed>24678015</pubmed></ref>

===References===
<references/>

2014 Group Project 5

2014-10-22T00:56:59Z

Z3418488: /* Hair */

{{ANAT2341Project2014header}}
=Integumentary=
==Introduction==
This page concerns the development of the integumentary system in the fetal stage of development, particularly its organs i.e. the skin, glands, hair, teeth, and nails. It explores the mechanism of development as well as the timeline of development. This page also outlines some recent findings on the development of the integumentary system, as well as historic findings. Finally, this page also explores some of the congenital abnormalities of the integumentary system, its mechanism or pathogenesis, clinical manifestations, and how they are treated or managed.

==Development Overview==
===Skin===

The skin consists of 2 layers: the outer layer (epidermis) and a deeper connective tissue layer (dermis).
*The epidermis is derived from the ectoderm. Initially it exists as only a single layer of ectodermal cells at 7-8 days of gestation. However, by about 13-14 weeks after gestation, a 3- layered structure of fetal epidermis exists- consisting of the stratum basale, 1 or 2 intermediate layers and the periderm. The peridermal cells eventually become desquamated and form part of the vernix cervix.
** The 5 definitive layers of the adult skin are evident in the human fetus after 22-24 weeks of gestation. Indirect influences form the dermis help differentiate the epidermis into: stratum basale, stratum spinosium, stratum granulosum, stratum lucidum and stratum corneum.
*The somatic mesoderm is the embryonic origin of the dermis. The mesoderm of the dermatones of the body, also contribute to the development of the dermis. Specifically though, in the head and neck region of the body, the dermis is derived from neural crest cells.
** The dermis is initially composed of just mesenchymal cells- loosely aggregated mesodermal cells. These mesenchymal cells later develop into fibroblasts- which function to secrete collagen and lay-down elastic fibers into the extracellular matrix.

3 other specialised cells of the epidermis also exists- these include melanoblasts, Langherhan cells and Merkel cells.
*Melanoblasts- are derived from neural crest cells that have migrated into the stratum basale. Mid-pregnancy, melanosomes are observed, differentiating the melanoblasts into melanocytes
*Langheran cells- are derived from bone marrow (originally form mesoderm) and migrate into the epidermis. They have the function of antigen presentation.
*Merkel cells- still have an uncertain origin. They have a function related to mechanoreception.

{| style="width:60%; height:125px" border="1" align="center"
|-
! Week !! Description !! Phase Diagram
|-
| Week 6-8|| In an electron micrograph study of the epidermis, the periderm and and basal layer of the developing skin was observed. || [[Image:Human_embryo_skin_8-9_week_EGA.jpg|100x100px|Weeks 6-8]]
|-
| Week 7-9 || In an electron micrograph study of the epidermis at weeks 7-9 of development, the stratified three-layer structure of the epidermis was observed. Kertain filaments have been encircled. || [[Image:Human_embryo_skin_9-11_week_EGA.jpg|100x100px| Weeks 7-9]]
|-
| Week 14 || By week 14, the basal layer, the intermediate layer/s and the periderm 3-layered structure can be observed in the fetus. By week 14, K17 can also be found in the basal and intermediate layers of the epidermis (In adult skin, K17 was not observed) || [[Image:Fetal_integumentary_histology_14w.jpg|100x100px| Week 14]]
|-
| Week 16 || In a study, by week 16, developing blood vessels were observed. CD31 and a sub-type of smooth-muscle actin stained positive in these observed developing blood vessels. || [[Image:Inaugumentary_week16.jpg|100x100px| Week 16]]
|-
| Week 18 || Example || [[Image:542px-Fetal_integumentary_histology_18.jpg|100x100px| Week 18]]
|-
| Week 19 || In a study, by week 19, as opposed to week 14, K17 was found present in the basal, intermediate and periderm layers. K17 also stained positive in the developing hair follicles. || [[Image:Inaugumentary-_Week_19.jpg|100x100px| Week 19]]
|-
| Week 20 || By week 20, hair follicles can be already be seen in the epidermis. The total number of intermediate layers has also increased || [[Image:Fetal_integumentary_histology_20.jpg|100x100px|Week 20]]
|-
| Week 22 || In an electron micrograph study at week 22 of development, kertanised epidermis was analysed. It was observed that glycogen was abundantly present throughout all epidermal layers. The included arrows, highlight the keratin filament bundles, which are now organised and peripherally placed. || [[Image:Human_embryo_skin_24_week_EGA.jpg|100x100px| Week 22]]
|-
| Adult|| In adult skin- a greater diversity of cells can be seen as more cells differentiate. Basal, spinous, granular and cornified cells are all example of such. In another study, chondroitin sulphate was observed in the basement membrane zone of the adult epidermis. In the same study, chondroitin sulphate was only observed towards the upper-part of the dermis. Also, elastin was present in the adult specimens, but not in the earlier fetal samples. || [[Image:Fetal_integumentary_histology_Adult.jpg|100x100px| Adult]] [[Image:542px-Fetal_integumentary_histology_Adult.jpg|100x100px| Adult]]
|}

<pubmed>19701759</pubmed>
<pubmed>PMC2113922</pubmed>

===Glands===
{| align="center" style="width:70%; height:200px" border=1
|-
! Gland Type !! Description
|-
| Sebaceous Glands|| *Sebaceous glands develop from the epithelial wall of the hair follicle.
*Vernix caseosa
Vernix caseosa is a material produced by sebaceous glands in the foetus in the last trimester of development <ref name="PMID15830002"><pubmed>15830002</pubmed></ref> and is characterised by it’s cheese-like appearance around the neonate at birth. The functions of vernix caseosa include:
*thermal regulation <ref name="PMID15830002"><pubmed>15830002</pubmed></ref>
*barrier to water loss (to keep fetal skin hydrated)<ref name="PMID21504444"><pubmed>21504444</pubmed></ref><ref name="PMID15830002"><pubmed>15830002</pubmed></ref>
*acid mantle development <ref name="PMID15830002"><pubmed>15830002</pubmed></ref>
*prevents the epidermis from water contact while epidermal cornification and formation of the stratum corneum occurs<ref name="PMID21504444"><pubmed>21504444</pubmed></ref>
|-
| Mammary Glands || *Mammary glands develop from the mammary ridge- a downgrowth of the epidermis (ectoderm) into the underlying dermis (mesoderm). This occurs at about week 6 of development. Prior to puberty, the mammary glands are anatomically indistinguishable.
|-
| Sweat Glands || *Eccrine and apocrine sweat glands develop from the downgrowths of the epidermis into the underlying dermis. It has been seen and detected in studies from week 21.
|}

{| style="width:40%; height:170px" align="center"
|-
| [[Image:Integumentary_histology_02.jpg|frame| 250x250px|Histology of eccrine sweat gland]] || [[Image:Integumentary-_sebaceous_gland_histology_01.jpg|frame|centre|250x250px|Histology of sebaceous gland]]
|}

::: Cite this page: Hill, M.A. (2014) Embryology Integumentary System - Gland Development. Retrieved October 7, 2014, from https://php.med.unsw.edu.au/embryology/index.php?title=Integumentary_System_-_Gland_Development
<references/>

===Hair===
[[Image:Hair_development_stages.jpg|frame|right|middle|300x250px|The stages of hair development]]

Hair originates from the ectoderm. At about 12 weeks, it is believed that specific signals from the dermis begin to induce hair follicle formation <ref name= PMID1566372><pubmed>1566372</pubmed></ref><ref name= PMID20590427><pubmed>20590427</pubmed></ref>. Through reciprocal interactions, cells from the stratum basale grow into the underlying dermis. The epithelial cells influenced by these dermal signals, develop a placode- a thickening of the columnar cells. Signalling from the placode than leads to the development of a dermal condensate, which further induces the downward growth of the placode. The hair follicle, continues to proliferate and enclose the dermal condensate, forming a deep, club-shaped hair bud, with an invaginated dermal papillae <ref name= PMID11841536><pubmed>11841536</pubmed></ref>. These dermal papillae are rapidly infiltrated by blood vessels and nerve endings. The epithelial cells within the hair bulb, then begin to differentiate into the germinal matrix – which grow, proliferate and keratinise to form the hair shaft and internal root sheet<ref name= PMID11841536><pubmed>11841536</pubmed></ref>. Other epithelial cells outside of the hair bud, form the external hair sheeth. Mesodermal cells of the dermis that surround the invaginating hair follicle form the dermal root sheeth and the arrecrtor pili muscles for hairs.

===Nail===
Together, fingernails and toenails are modifications of the epidermis, embryologically derived in humans from the same origin of ectodermal skin cells.
* Nails commence development at the tips of the digits around the stage of 10 weeks, with the initiation of fingernail growth preceding that of toenails by approximately 4 weeks. The earliest recognisable stages of nail development by week 10 are thickenings of epidermis, known as the primary nail fields, repositioning from the initial ventral surface to the eventual dorsum of each digit.
* The nail fields are bounded by folds of epidermis: the shallower lateral nailfolds, which adjoin into the much deeper proximal nailfold.
* The true nail is developed via the keratinization of cells within the proximal nailfold that proliferate over nail field, developing into the nail plate.
*Initially the developing nail is covered by a thin layer of epidermis, the eponychium (corneal layer of epidermis) that at later fetal stages declines to expose the free nail, however endures as the cuticle. Beneath the free end of the nail, epidermal cells aggregate to form the mass known as the hyponychium.
* By 32 and 36 weeks of development, the fingernails and toenails respectively reach the tips of the digits and toes.

:::Cite this page: Hill, M.A. (2014) Embryology Integumentary System - Nail Development. Retrieved October 7, 2014, from https://php.med.unsw.edu.au/embryology/index.php?title=Integumentary_System_-_Nail_Development

- need to reference this website: http://discovery.lifemapsc.com/library/review-of-medical-embryology/chapter-75-development-of-the-nails + textbook info here

{| class="wikitable"
|-
! Header text !! Header text
|-
| Week 9 || The primitive nail beings to from
|-
| Week 10|| The primary nail field is establish
|-
| Week 11 || Distal ridges of nail bed keratinise.
|-
| Week 13 || Early nail matrix.
|-
| Week 20 || Nail plate begins to grow over the nail bed.
|-
| Week 24 || Free nail plate is visible to the naked eye.
|}

===Teeth===

The ectoderm and the associated underlying layer of neural crest cells, are the origin for teeth development. As the oral epithelium grows and proliferates, it has a downward movement into the underlying neural crest layer. This leads to the formation of the dental lamina. These dental lamina, then, gives rise to tooth buds. These tooth buds, later form and develop into enamel organs. With further development, these enamel organs give rise to ameloblasts- which produce enamel. The dental papilla, on the other hand is formed by the neural crest cells which underlie the enamel organs. These dental papillae than give rise to the dental pulp and odontoblasts- which produce predentin and dentin, in the adult body.

[[Image:Tooth development stage.jpg|frame|left|middle|425x300px|The stages of embryonic teeth development]]

{| class="wikitable"
|-
! Stage!! Week !! Description
|-
| (A) Lamina|| Week 6 || The oral ectoderm, closely interacts with the neural crest ectomesenchyme. In the Lamina stage, teeth may grow only within the epithelium.
|-
| (B) Placode|| Week 7 || The dental lamina and and the dental placodes arise, due to specific signals from adjacent epithelial cells
|-
| (C) Bud || Week 8 || Tooth buds are formed, as the epithelium cells interact with the messenchyme. This occurs at the sides of the dental placodes. Also, as opposed to the earlier Lamina stage, in the Bud stage, teeth may now only grow within the ectomesenchyme
|-
| (D) Cap|| Week 11 || After folding, the bud takes upon the shape of an inverted cap
|-
| (E) Bell|| Week 14 || The bud refolds once again, this time taking upon the shape of a bell
|}

<html5media height="300" width="400">https://www.youtube.com/watch?v=nRH8M-arC58</html5media>

===References===
<references/>
<pubmed>19266065</pubmed>| [http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=2651620&tool=pmcentrez PMCID: PMC2651620]

Int J Biol Sci. 2009; 5(3): 226–243.
Published online 2009 February 24.

Copyright © Ivyspring International Publisher. This is an open-access article distributed under the terms of the Creative Commons License (http://creativecommons.org/licenses/by-nc-nd/3.0/). Reproduction is permitted for personal, noncommercial use, provided that the article is in whole, unmodified, and properly cited.

==Some Recent Findings==
{|
|-bgcolor="F5FFFA"
|
* '''Expression of caspase-14 and keratin-19 in the human epidermis and appendages during fetal skin development:''' In recognition of the vital roles of CASP-14 and CK-19 in human skin development and maturation, the purpose of this study was to primordially investigate the expression of these two molecular factors throughout the stages of human fetal skin development from gestation to the postnatal period in order to evaluate their singular and collective functions in epidermal and associated appendage maturation and processes of differentiation and re-modelling of human fetal skin. The results of the immunohistochemical study showed the expression of CASP-14 to be a biochemical marker of human epithelial differentiation during gestation, whilst CK-19 was a marker for epidermal stem cells nests of the stratum basale of the fetal epidermis and appendages. CASP-14 was concentrated within the more differentiated fetal epidermal layers, progressively declining from the basal layer toward term whilst CK-19 showed reduced expression with progressive epidermal development of the fetal stages and was a biochemical marker for epidermal stem cells nests of the stratum basale showing marginal conservation in basal cell nests at term and postnatally. Expression of CASP-14 within the epidermal appendages of the hair follicles and sebaceous glands were concentrated within the greater differentiated inner root sheath whilst CK-19 was greatly concentrated within the outer root sheath. Inconsistent patterns of expression of both molecules CASP-14 and CK-19 were demonstrated within eccrine sweat glands. <ref name=PMID23377137><pubmed>23377137</pubmed></ref>
|}

{|
|-bgcolor="F5FFFA"
|
* '''Cxcr4 is transiently expressed in both epithelial and mesenchymal compartments of nascent hair follicles but is not required for follicle formation:''' Cellular signalling between mesencyhmal and epithelial layers of the developing skin initiate an assortment of morphogenetic events throughout embryogenesis, involving the formation of the skin and in particular, the development of hair follicles (HF). The aims of this study was to identify the specific signalling pathways associated with HF morphogenesis during the primary stages of mouse hair follicle development through the investigation of the precise expression patterns and role of the Cxcr4 receptor in two specialised cell types- mesenchymal dermal condensate (DC) cells and epithelial placode cells. Staining patterns of the Cxcr4 receptor in the budding HF revealed a high concentration within epithelial placode cells and later DC cells in developing HF’s, signifying a shift of expression between epithelial and mesenchymal layers during HF morphogenesis. The functionality of the Cxcr4 receptor was tested through Cxcr4 receptor ablation in both the mesenchymal and epithelial layers of the developing embryonic skin of conditional knockout mice (cKO) and was verified through immunofluorescence staining techniques. Normal HF development was still induced despite the absence of Cxcr4 expression in the skin of the cKO mice and numbers were comparable to those found in the wild-type (WT) control group in embryonic and postnatal skin groups demonstrating that the chemokine signalling through the Cxcr4 receptor is inessential for normal early HF development (Figure 1). <ref name= PMID25066162><pubmed>25066162</pubmed></ref>
|}

{| style="width:40%; height:170px" align="center"
|-
| [[Image: Eosin_staining_of_mouse_embryonic_skin.png|frame|250x250px|Figure 1: Hematoxylin/ eosin staining of embryonic skin sections and macroscopic view of external hair shafts of mouse. Cxcr4 receptor ablation in condensates and placodes show no effect on mouse HF morphogenesis. Hair follicle and shaft develop normally and in comparable numbers in both Tbx18cre (a) and Krt14-cre (b) Cxcr4fl/fl cKO mice.]] || [[Image: Screen Shot 2014-10-19 at 11.09.42 PM.png|frame|right|middle|300px|Figure 2: The expression of stem cell marker, nestin and proliferative marker, Ki67 in the developing human nail.]]
|}

{|
|-bgcolor="F5FFFA"
|
* '''The ventral proximal nail fold: stem cell niche of the nail and equivalent to the follicular bulge--a study on developing human skin:''' In comparison to the characterization of the stem cell niche within the folliculosebaceous-apocrine unit, the local microenvironment of stem cells within the human nail organ is yet to be characterized. The aims of the current study was through immunohistochemical analysis to describe the expression pattern of six follicular stem cell markers; cytokeratin 15 (CK15, two clones), cytokeratin 19 (CK-19), PHLDA1, CD200 and nestin within the developing human nail and compare it with the embryonic and fetal human hair follicle. In addition, locations of vast proliferative activity within the nail were assessed using labeling with Ki-67. The stem cell markers CK15 (both clones), CK19, PHLDA1, CD200 and nestin showed no staining within the nail and hair matrix samples, however were present within the central proximal nail fold and follicular bulge. The biochemical marker for proliferation, Ki-67 showed the highest concentration of proliferative cells within the hair germ, lower regions of the hair peg and in the hair matrix. In the developing human nail the expression of Ki-67 was most prominent within the nail bed epithelium and the later nail matrix. In contrast the lowest numbers of kI-67 positive staining cells were located in regions of stem cell niches of the follicular bulge and proximal ventral nail fold as stem cells divide infrequently (Figure 2). Throughout the course of embryonic development these stem cell markers exhibit a highly specific expression pattern both within the nail and the hair follicle. The results seem to suggest that during embryonic envelopment the proximal ventral nail fold is the niche for nail stem cells. <ref name= PMID22804461><pubmed>22804461</pubmed></ref>
|}

{|
|-bgcolor="F5FFFA"
|
* '''Msx1 and Tbx2 antagonistically regulate Bmp4 expression during the bud to cap stage transition in tooth development:''' The expression of Bmp4 is essential for the bud to cap phase transition in embryonic dental development and is accordingly firmly regulated, with earlier stages of expression localised within the dental epithelial placode developing in to a later forms of expression in the dental mesenchyme. Numerous transcription factors including Pax 9, Osr2, Barx 1, Msx1, have been identified to prompt and maintain Bmp4 expression in these critical stages of tooth development. In particular Msx1 is one such transcription factor induced through epithelial Bmp4 expression and in turn is essential for the induction and regulation of dental mesencyhmal Bmp4 expression. The results of this investigation have demonstrated the expression of an additional transcription factor, Tbx2, induced through epithelial Bmp4, within the dental mesenchyme at bud stage of dental development. To determine a functional connection between the Msx1 and Tbx2 transcription factors, a cross was made between Tbx2 and Msx1 mutant mice. The data demonstrates that bud phase tooth arrest in Msx1-/- mice is moderately restored in Msx1-/-. Tbx2+/- compound mutants. The maintenance of Tbx2 expression in the Msx-/- arrested tooth buds exhibits that the expression of Tbx2 is not dependant on that of Msx1. This restoration in the developmental process is associated with the establishment of the enamel knot (EK) and the reinstatement of mesencyhmal Bmp4 expression. Knockout of Tbx2 resulted in an increase mesencyhmal Bmp4 expression. This data demonstrates that subsequent to the induction of epithelial Bmp4, both transcription factors Msx1 and Tbx2 in turn antagonistically regulate odontogenic activity that results in EK formation as well as mesenchymal Bmp4 expression at the vital bud to cap phase transition in embryonic dental development resulting in appropriate morphogenesis and patterning. <ref name= PMID23720046><pubmed>23720046</pubmed></ref>

|}

{| class="wikitable mw-collapsible mw-collapsed"
! More Recent Papers
|-
|
<pubmed>23826487</pubmed>
<pubmed>22342389</pubmed>
<pubmed>24911066</pubmed>
<pubmed>25143675</pubmed>
<pubmed>23271751</pubmed>
<pubmed>25249463</pubmed>
<pubmed>23097355</pubmed>
<references/>
|}

==Historic Findings==

Knowledge of the Integumentary expands in conjunction with technological developments that allow observation of microscopic structures. Historically animal models have been used to map the stages in the development of the fetal integumentary system.

===Skin===

In 1900 Bardeen C. R used the pig animal model to study the histogenesis of the dermomyotomes and nervous appratus. Bardeen and other scientists established that the human skin results from the union of the epithelial material derived from the ectoderm (epidermis) and the connective tissue origination from the mesoderm (dermis).

http://journals.lww.com/plasreconsurg/Citation/1949/07000/CLINICAL_ASPECTS_OF_EMBRYOLOGICAL_SKIN.8.aspx
Bardeen, C. R. (1900). The development of the musculature of the body wall in the pig, including its histogenesis and its relations to the myotomes and to the skeletal and nervous apparatus. Johns Hopkins Hosp. Rep, 9, 367-399.

===Glands===

Sebacious glands / Sweat glands / Mamailliary

In the 1968 Robins and Breathnatch investigated the development on the sebacious and apocrine swelling in the skin, which where closely associated with development of the hair follicle. They observed differentiation of desmosomes and development of cytoplasmic contents of the cell.

===Hair===

he major anatomic details of hair development in the human foetus have been established by studies with light microscopy. Electron microscopy was not commonly used to until recently and so little was known about the ultrastructure of the skin. Over the past few years, reports have been published on the epidermal melanocytes and periderm.

* '''1958''' - Pinkus established the following stages of fetal hair follicle development: pre-germ, hair-germ, hair-peg,andbulbous-peg stages. Pinkus also determined that the developed hair fibres grow through the epidermis and appears at the level of the skin at around 19-21 weeks of development. The lanugo (foetal) hair is extremely fine with no medulla and a tip free of pigment.

* '''1968''' - Breathnach and Smith determined the fine structure of the cells of follicle and dermal papilla in the first two weeks of fetal development. The Peripheral Nerves, the sweat duct and nail development were also explored and the interrelationship of cells at particular foetal stages was deduced. These studies, and other laboratory animals, have provided information on the differentiation of cells and tissue of some functional importance and underline the role of cells and tissues.

Robertson, J. R. (Ed.). (2002). Forensic examination of hair. CRC Press.

* '''1959''' - Chase and Eaton's investigated fetal hair follicle development. With key observations in understanding the cycling nature of hair follicle growth, following development. Development begins with the downwards growth of the follicle structure from the level of the dermis. The follicle is a processes during the quiecent phase thought he adipose layer during gowth and differntiation. They also established that upward movement of hair inovlves the addition of next cells from the matrix of the follicle and an enlargement of each cell. Furthermore their research also showed that the epidermal and dermal layers were dynamic and interacting with each other. The most significant developments in the understanding of hair follicle development came from studies investigating the differentiation pattern of cells as the follicle develops. <ref name= PMID5656140><pubmed>5656140</pubmed></ref>

<pubmed>5656140</pubmed>
<pubmed>4097391</pubmed>

Determined that the hair fibre finally breaks through the epidermis and appres about the skin at around 19-21 weeks of development. The lanugo (foetal) hair is extremely fine with no medulla and a tip free of pigment.

===Nail===

Microscopy and staining techniques have been essential tools in study on developmental anatomy and physiology of the nail. Thus as technology advances scientists have been able to uncover the morphological changes during nail development. A review of the history allows us to recognise the major contributor to study of this field. History also reveals the interesting debate on the origins of keratinised cells which migrate to form the nail palate in weeks 20-24 of fetal development.

[[Image:Nail Plate Development - Pinkus .jpg|frame|right|middle|180x150px|]]

* '''1883''' - Unna published a chapter on the anatomy and development of the human nail in the German textbook "Ziemsssen's Handbuch der Speciell Pathologie und Therapie" - Ziemsssen 's manual of special pathology and therapy.
* '''1927''' - Pinkus conducted his earliest investigations into fetal nail development. His findings were published in the "Handbuch Der Haut und Geschlechtskrankeiten” - Manual of Skin and Venerail Disease.
German scientists Unna and Pinkus contributed to the understanding of the anatomy. Both scientists proposed that the structures known as the nail matrix gave rise to the entire nail plate.

[[Image:Nail Plate Development -Lewis .jpg|frame|right|middle|160x135px|]]

* '''1954''' - Barton and Lewis conducted a through investigation on the microscopic features of the foetal and mature nail and surrounding soft tissue. Lewis challenged the current thought and proposed a tri-partite origin of the nail plate from three germinative tissues (1) the proximal nail fold (2) the matrix and (3) bed.
Prior to the 1900’s it was difficulty in obtaining normal foetal specimens. Furthermore, the histological staining techniques used to prepare slides of nail tissue often damage the specimen and little detail could be seen during the microscopic examinations. Barton and Lewis conducted this investigation in hopes that a better understanding of the normal developmental anatomy and physiology would assist physicians in diagnosing and treating abnormalities.

* '''1959''' - Samman carried out an investigation on the blood supply of the human toe nail. It was thought that a deeper understanding of morphology of the vasular supply might shed light on the genesis of the nail palate. Samman studied the morphology and distribution of blood vessels with in the nail found capillary loops through out the nail fold and concluded that this supports the theory of multiple sites giving rise to the nail plate.

* '''1963''' - Zaias conducted a number of studies on the embryology of the human nail. This investigation contributed to our understanding of different stages in foetal nail development. Zaias studied an number of foetal specimens at different stages in development. As a result, Zaias was able to propose a rough timeline highlighting morphological hallmarks in normal nail development.
* '''1968''' - Zaias and Alvazer investigated the formation of the primate nail plate. An autoradiographic study in the squirrel monkey.
The current understanding of fetal nail development is a summation contributions of many researches in the international scientific community. Today research continues, technology allows exploration beyond macroscopic and microscopic morphological changes in the fetal nail. Now the aim is to understand the molecular signalling with in the epidermal cells which drives this process.

<ref name= PMID13206419><pubmed>13206419</pubmed></ref> -- <pubmed>13206419</pubmed> -- Microscopic studies of fetal and mature nail and surrounding soft tissue. Lewis
<ref name= PMID14441224><pubmed>14441224</pubmed></ref> -- <pubmed>14441224</pubmed> -- The human toe nail. Its genesis and blood supply.
<ref name= PMID6161584><pubmed>6161584</pubmed></ref> -- <pubmed>6161584 </pubmed> -- Ultrastructure and Growth of Human Nails
<ref name= PMID14003041><pubmed>14003041</pubmed></ref> -- <pubmed>14003041</pubmed> -- Embryology of the Nail Zaias

===Teeth===
<ref name= PMID5267156><pubmed>5267156</pubmed></ref> -- <pubmed>5267156</pubmed>

==Abnormalities==

===Aplasia Cutis Congenita===
[[Image:Cutis aplasia.jpg|frame|right|middle|250x187px|Aplasia cutis congenita at the scalp]]
Aplasia cutis congenita (ACC) is a rare skin abnormality, characterised by the absence of all layers of the skin. It is most common to occur on the scalp (70%), specially the vertex. In severe cases, the defect can go as deep as the bone or the dura. Other sites of ACC include the skin of the limb regions. “ACC occurs in approximately 1 in 10000 live births, with a female-to-male ratio of 7:5.” The specific aetiologic agent for ACC is still unknown. It has been suggested to be genetic and/or environmental. The damage to the vertex is suggested to be the result of the biomechanical stretch at this area when the fetal brain is growing.<ref name= PMID22549580><pubmed>22549580</pubmed></ref>

Presently, ACC is managed via conservative treatments or surgical treatments. Conservative treatments refer to basic wound treatments and preventing infection with the use dressings and antibiotics. Surgical treatments, specifically scalp reconstruction procedures, aim to reconstruct the damage to the skin through skin grafts, local scalp flaps, and pericardial scalp flaps. Large defects are often treated using surgical treatments.<ref name= PMID23147310><pubmed>23147310</pubmed></ref>

===Dystrophic Epidermolysis Bullosa===
[[Image:Dystrophic Epidermolysis Bullosa lesions.jpg|frame|right|sub|270x230px|Severe skin lesions due to Dystrophic epidermolysis bullosa.<ref name="PMID23739692"><pubmed>23739692</pubmed></ref>]]
Dystrophic Epidermolysis Bullosa (DEB), a type of epidermolysis bullosa, is a genetic disease of the skin, usually present at birth or at an early age<ref name= PMID252845240><pubmed>25284524</pubmed></ref>. Currently, around 400,000 - 500,000 people are affected with the disease<ref name= PMID252845240><pubmed>25284524</pubmed></ref>. It is characterised by the fragility of the skin<ref name= PMID252845240><pubmed>25284524</pubmed></ref>, where it blisters upon minimal trauma and scars<ref name= PMID19945622><pubmed>19945622</pubmed></ref>, usually at the extremities<ref name= PMID252845240><pubmed>25284524</pubmed></ref>. It is caused by a mutation in collagen VII gene (COL7A1)<ref name= PMID19945622><pubmed>19945622</pubmed></ref><ref name= PMID24860657><pubmed>24860657</pubmed></ref>, which is responsible for the the formation of anchoring fibrils<ref name= PMID19945622><pubmed>19945622</pubmed></ref>. Anchoring fibrils are responsible for dermal-epidermal adherence<ref name= PMID19945622><pubmed>19945622</pubmed></ref>, that is why it’s loss of function results to blistering of the skin. In some cases, even teeth and nails are affected. Teeth of patients with DEB have enamel defects and when combined with poor oral hygiene, it may lead to decay. Nails of DEB patients are often dystrophic and will eventually be lost.<ref name= PMID252845240><pubmed>25284524</pubmed></ref>

There are currently no known cures for DEB; however there are techniques to manage the clinical manifestations of the disease, which include:
*wound care<ref name= PMID19945622><pubmed>19945622</pubmed></ref>
*preventing factors that may cause blistering<ref name= PMID19945622><pubmed>19945622</pubmed></ref>
*using aqueous disinfectants - highly effective<ref name= PMID19945622><pubmed>19945622</pubmed></ref>
*dental care<ref name= PMID252845240><pubmed>25284524</pubmed></ref>:
:-use of topical fluoride
:-careful prophylaxis
:-use of topical antibiotics to prevent secondary infections<ref name= PMID24860657><pubmed>24860657</pubme></ref>

One study is currently exploring the potential of protein therapy as a treatment for DEB. Their results show that intradermal injection of recombinant human collagen 7 in mice with DEB led to “restoration of C7 and anchoring fibrils.”<ref name= PMID19018253><pubmed>19018253</pubmed></ref> Other techniques that aim to restore C7 include:
*bone marrow transplant- improved blistering in mice specimen and increase survival rates<ref name= PMID24860657><pubmed>24860657</pubmed></ref>
*hematopoietic cell transplant (HCT)- increased deposition of C7 in injured skin<ref name= PMID24860657><pubmed>24860657</pubmed></ref>

===Congenital Alopecia Areata===
[[Image:Alopecia Areata.jpg|frame|right|middle|270x220px|Patches of hair loss: a sign of alopecia areata.<ref name="PMID23960401"><pubmed>23960401</pubmed></ref>]]
Alopecia areata (AA) is an abnormality of the hair affecting anagen hair follicles, characterised by well-demarcated patches of hair loss. It is non-scarring and can occur on the scalp and/or the body. 90% of AA cases occur on the scalp. 5%-10% of patients with AA lose all hair on their scalp; this is called alopecia totalis. While others lose all of their body hair, this is called alopecia universalis. <ref name= PMID17269961><pubmed>17269961</pubmed></ref> Its pathogenesis is considered to be both genetic and autoimmune. There is an abnormality with the genes related to the immune system and to the hair follicles. And histopathology shows signs of lymphatic infiltration of the hair follicles and the loss of these scalp lymphocytes allow hair follicles to recover.<ref name= PMID16338213><pubmed>16338213</pubmed></ref> High frequencies of catagen and telogen hair follicles are also present in areas affected by AA.<ref name= PMID17269961><pubmed>17269961</pubmed></ref>

There is currently no cure for AA. There are several treatments to combat AA but none of these have led to remission of the disease, the most effective being corticosteroids and topical immunotherapy.<ref name= PMID17269961><pubmed>17269961</pubmed></ref> A new method of treating alopecia areata is currently being studied. Transepidermal drug delivery (TED) is a new treatment that functions by creating micro-channels in the epidermis. By doing so, drug delivery to the skin is improved. This treatment was highly effective and had lower rates of side effects, e.g. pain, compared to previous treatments.<ref name= PMID25260052><pubmed>25260052</pubmed></ref>

===Harlequin Ichthyosis===
[[Image:Harlequin Ichthyosis.jpg|frame|right|middle|250x200px|A baby with harlequin ichthyosis.<ref name="PMID24520234"><pubmed>24520234</pubmed></ref>]]
Congenital ichthyosis is an autosomal recessive disease of the skin, characterised by visible and excessive scaling of the skin and hyperkeratosis, i.e. thickening of stratum corneum layer of the epidermis and in some cases, hypohidrosis, i.e. the lack of ability to sweat. <ref name= PMID19824737><pubmed>19824737</pubmed></ref> Harlequin ichthyosis (HI) occurs only in 1 in 1,000,000 babies. It is life-threatening in the first few weeks and/or months of the neonate.<ref name= PMID19824737><pubmed>19824737</pubmed></ref> The thick skin can restrict movement of the baby and sometimes constrict extremities and lead to necrosis then autoamputation.<ref name= PMID23419760><pubmed>23419760</pubmed></ref> Babies with HI are also characterised by bilateral ectropion (everted eyelids), eclabium (everted lips), and underdeveloped nose.<ref name= PMID23419760><pubmed>23419760</pubmed></ref> In 50% of HI cases, respiratory failure is often the cause of death.<ref name= PMID24124810><pubmed>24124810</pubmed></ref> This disease is caused by a nonsense mutation in the ATP-binding-cassette A12 (ABCA12) gene, which is responsible for encoding a lipid transporter essential for the regulation of lamellar bodies. <ref name= PMID19824737><pubmed>19824737</pubmed></ref><ref name= PMID23419760><pubmed>23419760</pubmed></ref><ref name= PMID24124810><pubmed>24124810</pubmed></ref>

There is currently no known cure for this disease. Management techniques include:
*Monitoring in neonatal intensive care units.
:-Temperature within the incubator is controlled to avoid fluctuation in body temperature and to stop sweating. <ref name= PMID19824737><pubmed>19824737</pubmed></ref>
*Mechanical removal of excess scales from the skin <ref name= PMID19824737><pubmed>19824737</pubmed></ref>
*Bathing to remove excess scales from the skin<ref name= PMID19824737><pubmed>19824737</pubmed></ref>
*Topical therapy - to reduce hyperkeratosis. <ref name= PMID19824737><pubmed>19824737</pubmed></ref><ref name= PMID24124810><pubmed>24124810</pubmed></ref>
*Use of oral retinoids - known to have high rates of survival.<ref name= PMID24124810><pubmed>24124810</pubmed></ref>

===Hypohidrotic Ectodermal Dysplasia===
[[Image:Oligodontia.jpg|frame|right|middle|250x187px|Oligodontia: a clinical manifestation of HED.<ref name="PMID21165248 "><pubmed>21165248 </pubmed></ref>]]
Hypohidrotic ectodermal dysplasia (HED) is the most of all ectodermal dysplasias, caused by an abnormality in the development of ectodermal tissues, which inlude skin, hair, teeth, sweat glands, and nails.<ref name= PMID20682465><pubmed>20682465</pubmed></ref><ref name= PMID24678015><pubmed>24678015</pubmed></ref> Patients with ectodermal dysplasia often have sparse hair and oligodontia, which is a condition where teeth are missing and are poorly developed.<ref name= PMID20682465><pubmed>20682465</pubmed></ref><ref name= PMID24678015><pubmed>24678015</pubmed></ref> Sweating is a very important function in the body in terms of thermoregulation. HED is mainly characterised by hypohidrosis due to the lack of sweat glands in the skin, which could lead to hyperpyrexia and sometimes death. In neonates, the mortality rate of HED reaches up to 30%, with the first year of life having the highest risk. <ref name= PMID20682465><pubmed>20682465</pubmed></ref> HED is caused by a genetic abnormality of the ectodysplasin A gene (EDA) and passed on by X-linked inheritance. The mutations of this gene results in the poor sweating ability or none at all in a person. The effects of this abnormality is usually more severe in males than in females. <ref name= PMID21357618><pubmed>21357618</pubmed></ref><ref name= PMID24678015><pubmed>24678015</pubmed></ref>

There is currently no pharmacological therapies for HED but there are methods applied to prevent the disease from aggravating. Neonates with HED are placed in incubators and monitored to prevent them from overheating. Management of this disease gets easier as the patient ages. Adults with HED can control their thermoregulation by staying in cool environments or drinking cold drinks to lower the body temperature. Currently, there are studies that aim to find a cure for this abnormality, e.g. gene replacement therapy in animal models.<ref name= PMID24678015><pubmed>24678015</pubmed></ref>

===References===
<references/>

Talk:2014 Group Project 5

2014-10-18T06:04:14Z

Z3418488: /* Week 11 */

2014 Group Project 5

2014-10-15T04:40:08Z

Z3418488: /* Glands */

2014 Group Project 5

2014-10-15T04:35:22Z

Z3418488: /* Glands */