Integumentary System - Nail Development

Embryology - 4 May 2024        Expand to Translate
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Introduction

This page introduces the development of nails, fingernails and toenails, these integumentary specializations in other species have been specialised as claws and hooves.

Each nail is convex on its outer surface, concave within, and is implanted by a portion, called the root, into a groove in the skin; the exposed portion is called the body, and the distal extremity the free edge.

Neonatal nail

Some Recent Findings

Incomplete development of the nail of the hallux in the newborn. "Between March and October 2008, the nails of 541 (252 females, 289 males) consecutively born neonates with an average age of 3.2 days were examined in the Neonatology Unit. Of these newborns with nail disorders, 36 were re-examined after a period that ranged from seven days to six months. The most frequent nail alteration was the incomplete development of the hallux nail, which was triangular - sometimes trapezoidal - shaped. This alteration, which had been previously reported in the literature as congenital hypertrophy of the lateral folds of the hallux, spontaneously regressed within one to three months in the infants re-examined. There was no associated inflammation or onychocryptosis at any time. The apparent hypertrophy of the nail folds seemed to be secondary to the lack of pressure of the nail lamina." Lyonization pattern of normal human nails. "To examine the X-inactivation patterns of normal human nails, we performed the human androgen receptor gene assay of DNA samples extracted separately from each finger and toe nail plates of nine female volunteers. The X-inactivation pattern of each nail was unique and constant for at least 2 years. ...These findings suggest that the composition of precursor cells of each nail is maintained at each site at least through several cycles of regeneration time, and that the nail plate has a longitudinal band pattern, each band consisting of cells with only one of the two X-chromosomes inactivated."

More recent papers

This table allows an automated computer search of the external PubMed database using the listed "Search term" text link. This search now requires a manual link as the original PubMed extension has been disabled. The displayed list of references do not reflect any editorial selection of material based on content or relevance. References also appear on this list based upon the date of the actual page viewing. References listed on the rest of the content page and the associated discussion page (listed under the publication year sub-headings) do include some editorial selection based upon both relevance and availability. More? References | Discussion Page | Journal Searches | 2019 References | 2020 References Search term: Nail Embryology <pubmed limit=5>Nail Embryology</pubmed>

Textbooks

The Nail

• 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

Development Overview

• Forelimb before hindlimb - week 10 fingernails, week 14 toe nails
• nail field - appears at tip and migrates to dorsal surface
• thickened epidermis - surrounding cells form nail fold
• keratinization of proximal nail fold forms nail plate

Nails reach Digit Tip

• week 32 fingernails
• week 36 toenails

Note that nail growth can be used as an indicator of prematurity.

Abnormalities

Ectopic Nail

Congenital ectopic nails are an extremely rare deformity.

Anonychia

A very rare abnormality resulting in an absence of nails. Can result from both genetic and environmental defects and be associated with a range of other abnormalities. Simple anonychia is the congenital absence of the nails without any other coexisting major congenital anomaly.

Witkop syndrome

An autosomal dominant genetic disorder characterized by the absence of several teeth and abnormalities of the nails.

References

Reviews

<pubmed>19932326</pubmed> <pubmed>18459147</pubmed> <pubmed>15468149</pubmed> <pubmed>12949775</pubmed> <pubmed>11710767</pubmed>

Articles

<pubmed>21387539</pubmed>

Search PubMed

Search Pubmed: Nail Development | Nail embryology

Additional Images

Category:Integumentary

Terms

• cuticle - tissue that overlaps the plate and rims the base of the nail
• hyponychium - the epithelium located beneath the nail plate
• lunula - half-moon at the base of the nail
• matrix - hidden part of the nail unit under the cuticle
• nail bed - skin beneath the nail plate
• nail folds - skin folds that frame and support the nail on three sides
• nail plate - visible part of the nail
• trachyonychia - nail plate roughness, pitting, and ridging affecting one or all twenty nails.

External Links

External Links Notice - The dynamic nature of the internet may mean that some of these listed links may no longer function. If the link no longer works search the web with the link text or name. Links to any external commercial sites are provided for information purposes only and should never be considered an endorsement. UNSW Embryology is provided as an educational resource with no clinical information or commercial affiliation.

• Embryo Images - Human (day 64) primary nail fields
• Key steps in the development of three major ectodermal appendages Tooth, Hair and Mammary Gland

Glossary Links

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Cite this page: Hill, M.A. (2024, May 4) Embryology Integumentary System - Nail Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Integumentary_System_-_Nail_Development

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