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Anatomy and Physiology of Nail Growth

Nails

The nail is the largest skin appendage. It grows continuously through life in a non-cyclical manner; its growth is not hormone-dependent. Nail Growth throughout our whole lives, but they grow slowest during the first four years of life, and fastest between the ages of 4 and 30 years.

The nail of the middle finger of the dominant hand grows fastest with approximately 0.1 mm/day, whereas the big toe nail grows only 0.03-0.05 mm/d. The nails’ size and shape vary characteristically from finger to finger and from toe to toe, for which the size and shape of the bone of the terminal phalanx is responsible. The distal phalanx provides bony support for the nail bed and is fractured in 50% of fingertip injuries. The nail bed lies protected between the nail plate and the distal phalanx. Fingernails grow more rapidly than toenails.

The nail apparatus consists of both epithelial and connective tissue components. The nail is fixed onto the bone through a highly vascularized dermis and two strong ligaments

Nail growth

  • Growth is fastest in the longer fingers and on people who bite their nails. The plate is produced by the nail matrix.
  • Normal growth is about 1,9 to 4,4 mm/ month (0,3 mm per day).  It needs two month for the plate to exit the proximal nail fold
  • It needs 6 months for a complete nail plate re-growth
  • The first plate is always irregular, so clinical results can only be evaluate at one year follow-up.
  • Nail plate growth stops for 3 weeks
  • The proximal part of the plate thicken
  • The growth accelerates for 50 days (the plate gets thinner)
  • Then the growth is slower for 30 days.
  • Apparition of a transverse line on the nail plate: the Beau’s line
  • Width is related to the duration of the trauma
  • It moves distally with time
  • It grow faster in summer compared to winter. 

Nail Plate

  • The nail plate is the actual fingernail, and it’s made of translucent keratin.
  • The pinkish appearance of the nail comes from the blood vessels underneath it.
  • The matrix epithelium is responsible for the production of the nail plate whereas the nail bed epithelium mediates firm attachment.
  • Is produced by the germinal matrix
  • Keratinic structure, partially transparent and curved both longitudinally and transversally
  • Three different layers, 0,5 mm thickness, 20% of water
  • Our nails are made up of keratinised cells.
  • These cells make up the nail plate, which is the structure that covers the nail bed and the matrix underneath it.
  • The nail plate curves slightly, which allows it to embed in the nail folds in the fingers. This is more marked in toe nails than in fingernails to provide additional strength to the foot.

Eponychium

  • The eponychium is more commonly known as the cuticle.
  • The cuticle is situated between the skin of the finger and the nail plate.
  • It fuses these structures together and provides a waterproof barrier.

Hyponychium

  • The hyponychium is the area between the nail plate and the fingertip.
  • It is the junction between the free edge of the nail and the skin of the fingertip.
  • It also provides a waterproof barrier.
  • The hyponychium is a specialized structure sealing the subungual space and allowing the nail plate to physiologically detach from the nail bed.
  • The hyponychium is located where the sterile matrix of the nail bed meets the skin of the fingertip under the nail.
  • The hyponychium is an area of heightened immune activity, where large amounts of immune cells such as lymphocytes are found.
  • As a result, infections underneath the nail are relatively rare unless continued soaking of the fingernail in solutions that injure or destroy the hyponychium occurs, allowing bacteria and fungus to penetrate beneath the nail.

Paronychium

  • The paronychium is the skin that overlaps onto the sides of the nail plate, also known as the paronychial edge.
  • Include all the soft tissues located under the nail plate
    • Nail (germinal) matrix,
    • Nail bed,
    • Hyponychium.
  • Soft-tissues aroud the plate (paronychium) proximal and lateral nail wall (fold) and the cuticle
  • The paronychium contributes to the stability of the nail and its adherence to the fingertip, and is located where the skin of the finger comes into contact with where the nail curves into the finger.
  • There is currently no specific function associated directly with the paronychium.

Nail production

  • The nail is made up of a substance called onchyn, which is produced by the death of germinal cells, which are cells that go on to become various types of cells.
  • The nail is formed by these cells as they are pressed upward.
  • The nail is produced in three areas of the perionychiumGerminal matrix,Sterile matrix

    Nail matrix.


Germinal matrix

  • The majority of the nail is produced by the germinal matrix (around 90% by volume).
  • This matrix extends from the base of the nail to the lunula.
  • Cells in the matrix replicate by a process where the cells flatten and are pressed forward and upward while retaining their nuclei (the central body within a cell).
  • This retention gives the nail its white colour through the arc of the lunula (the “moon” of the nail).
  • Where the nuclei are lost, the nail is clear, showing the pink colouring of the nail bed through it.
  • The only site of production of the nail plate
  • Extend distally to the lunula
  • Also extend over the nail plate
  • Cannot be replaced by any other tissue

Sterile matrix

  • The sterile matrix contributes to nail production as the nuclei of its cells disintegrate.
  • When this occurs, 1-2 layers of germinal cells push upward and become attached to all the surrounding nail cells.
  • These cells then become part of the nail that has been produced by the germinal matrix, and progresses towards the end of the nail with it.
  • The nail therefore gets thicker towards the end to compensate for surface wear.

Nail matrix

  • The nail matrix produces the nail in a manner similar to the sterile matrix on the roof of the nail.
  • The nail matrix produces the shine of the nail, and removing this part of the nail results in the shine of the nail being lost and can result in an irregular surface.

Vascularization

  • 4 origins
  • Flint’s artery
  • Arch of the proximal fold
  • Transverse arches under flint’s ligament
  • Distal arteries coming from the pulp

Development of nails

  • 9 weeks after fertilization – The first embryonic element of the nail appears.
  • 13 weeks – The nail area in the finger is well defined.
  • 14 weeks – The nail plate appears from underneath the nail fold.
  • 17 weeks – The nail bed is is mostly covered by the nail plate.
  • 20 weeks – Both the nail unit and the fingers grow in tandem from this point.
  • Birth – The nail plate extends to the end of the fingertip.