Nail anatomy and physiology
Published on: Mar 3, 2016
Transcripts - Nail seminar
APPLIED ANATOMY AND
PHYSIOLOGY OF NAIL
ANATOMY AND BIOLOGY
OF THE NAIL UNIT
nail apparatus - strong, relatively
protective covering for fingertip
allows precision and delicacy when picking up
primitive epidermis – 9 - 20th wks.
matrix cells show postnatal-type cell division
differentiation and keratinization
nail plate begins to form and move distally
nail bed loses its granular layer at this stage.
36 wk: nail plate reaches the tip of the digit
and is surrounded by prominent lateral nail
folds and a well-formed cuticle.
NAIL BASIC STRUCTURE
1/4 nail is covered by the proximal nail fold
Lunula (half-moon, lunule)
Under proximal part of nail
most distal region of the matrix
most prominent on thumb & great toe
may be partly or completely concealed by the
proximal nail fold in other digits
nail plate distal to lunula usually appears
pink, due to its translucency, which allows the
redness of the vascular nail bed to be seen
PROXIMAL NAIL FOLD
two epithelial surfaces, dorsal and ventral, at the junction of
the two, the cuticle projects distally onto the nail surface.
LATERAL NAIL FOLDS
continuity with the skin on the sides of the digit laterally, and
medially they are joined by the nail bed.
subdivided into dorsal (ventral aspect of the proximal nail
fold), intermediate (germinal matrix or matrix) and ventral
(nail bed) sections.
two distinct areas may be visible, THE PROXIMAL LUNULA
AND THE LARGER PINK ZONE on seeing nail plate from
On close examination, two further distal zones can often
be identified , the distal yellowish-white margin and
immediately proximal to this the onychodermal band
The proximal nail folds are similar in structure to the
devoid of dermatoglyphic markings and
From the distal area of the proximal nail fold the
cuticle adheres to the upper surface of the nail plate
serves to protect the structures at the base of the
nail, particularly the germinal matrix, from
NAIL MATRIX (INTERMEDIATE
Nail matrix produces the nail plate
The nail matrix contains melanocytes in the
lowest three cell layers and these donate pigment
to the keratinocytes.
there is presence of 6.5 melanocytes per
millimetre of matrix basement membrane
Langerhans cells are detectable in the matrix by
CD1a staining, and the matrix appears to contain
basement membrane components
Nail bed consists of epidermis with underlying
connective tissue closely apposed to the periosteum
of the distal phalanx.
There is no subcutaneous fat in the nail bed
The nail bed epidermis is usually two or three cells
The nail bed dermal collagen is mainly orientated
vertically, being directly attached to the phalangeal
periosteum and the epidermal basal lamina.
Within the connective tissue network lie blood
vessels, lymphatics, a fine network of elastic fibres
and scattered fat cells; at the distal margin, eccrine
sweat glands have been seen
The nail plate comprises three horizontal layers: a
thin dorsal lamina, the thicker intermediate lamina
and a ventral layer from the nail bed
The nail plate contains significant amounts of
phospholipid, mainly in the dorsal and
intermediate layers, which contributes to its
The nail plate is rich in calcium, found as the
phosphate in hydroxyapatite crystals
Calcium does not significantly contribute to the
hardness of the nail
Nail keratin analysis shows essentially the same
fractions as in hair
amino acid analysis shows higher cysteine, glutamic
acid and serine, and less tyrosine in nail compared
normal nail demonstrates that the suprabasal keratin
pair K1/K10 is found on both aspects of the proximal
nail fold and to a lesser degree in the matrix.
However, it is absent from the nail bed.
The nail bed contains keratin synthesized in normal
basal layer epithelium, K5/K14, which is also found in
keratin pair K6/K16 are present in the nail bed but
not in the germinal matrix
BLOOD SUPPLY OF NAIL
rich arterial blood supply to the nail bed and matrix
derived from paired digital arteries, a large palmar and
small dorsal digital artery on either side.
There are two main arterial arches (proximal and distal)
supplying the nail bed and matrix, formed from
anastomoses of the branches of the digital arteries.
Within the matrix, vessels are longitudinal with a
There are many arteriovenous anastomoses beneath the
nail— glomus bodies—which are concerned with heat
Glomus bodies are important in maintaining acral
circulation under cold conditions: arterioles constrict with
cold but glomus bodies dilate.
Arterial supply of the distal
NAIL GROWTH AND MORPHOLOGY
immunohistochemistry, autoradiography and
direct measurement of matrix product (i.e. nail
plate) by ultrasound ,micrometer or histology.
The rate of nail growth is about 3 mm/month for
finger nails and about 1 mm/month for toe nails
The nail grows flat, rather than as a
heaped-up keratinous mass
factors probably responsible to produce a
relatively flat nail plate are
orientation of the matrix rete pegs and papillae
the direction of cell differentiation and moulding of
the direction of nail growth between the proximal
nail fold and distal phalanx.
Containment laterally within the lateral nail folds
assists this orientation
the adherent nature of the nail bed
PHYSIOLOGICAL AND ENVIRONMENTAL
FACTORS AFFECTING THE RATE OF NAIL
PREGNANCY FIRST DAY OF LIFE
YOUTH,INCREASING AGE OLD AGE
FINGERS TOES AND THUMBS
MALE GENDER FEMALE
RIGHT HAND NAILS LEFT HAND NAILS
PATHOLOGICAL FACTORS AFFECTING THE RATE
OF NAIL GROWTH
PSORIASIS FINGER IMMOBILIZATION
LEVODOPA YELLOW NAIL
IDIOPATHIC POOR NUTRITION
NAILS IN CHILDHOOD
In early childhood, the nail plate is relatively thin
and may show temporary koilonychia
nails are also prone to terminal onychoschizia
(lamellar splitting),most prominent on the
Beau’s lines can be seen in up to 92% of
normal infants between 8 and 9 weeks of age
A herringbone pattern is common in children
and gradually diminishes with time, reflecting a
gradual matrix maturation
NAILS IN OLD AGE
The whole subungual area in old age may
show thickening of blood vessel walls with
vascular elastic tissue fragmentation.
The nail plate becomes pallor, dull and
opaque with advancing years
white nails similar to those seen in
cirrhosis, uraemia and hypoalbuminaemia
may be seen.
NAIL SIGNS AND SYSTEMIC DISEASE
ABNORMALITIES OF SHAPE
In clubbing there is increased transverse and longitudinal
nail curvature with hypertrophy of the soft-tissue
components of the digit pulp.
Hyperplasia of the fibrovascular tissue at the base of the
nail also occurs.
Pathological associations of clubbing include ---
inflammatory bowel disease, carcinoma of the bronchus
In forms associated with bronchiectasis or
neoplasm, prominent inflammatory joint signs may also be
seen, resulting in hypertrophic pulmonary osteoarthropathy
CLINICAL PICTURE OF CLUBBING
Lovibond’s angle is found at the
junction between the nail
plate and the proximal nail
fold, and is normally less than
This is altered to over 180° in
Curth’s angle at
the distal interphalangeal joint is
normally about 180°. This is
diminished to less than 160° in
Schamroth’s window is seen when the dorsal
aspects of two fingers from opposite hands
are opposed, revealing a window of
light, bordered laterally by the Lovibond
angles. As this angle is obliterated in
clubbing, the window closes.
In some cases of bronchiectasis, a variant of
clubbing, shell nail syndrome is seen.
Distugunished from clubbing by the presence
of atrophy of underlying bone and nail bed
Greek: koilos, hollow; onyx, nail
In koilonchyia there is reverse curvature in
the transverse and longitudinal axes giving a
concave dorsal aspect to the nail
most prominent in the thumb or great toe.
common in infancy in toe nail
Its persistence may be associated with a
deficiency of cysteine-rich keratin
a familial pattern which may be autosomal
Dominant may be seen in some families
Most common systemic association is with
iron deficiency and haemochromatosis
Also known as trumpet or involuted nail
Pincer nail describes a dystrophy where nail
growth is pitched towards the
midline, combined with increased transverse
There are 3 variants of pincer nail
1) In the inherited version there is often a gradient
of involvement, radiating from the thumbs and
big toes outwards, which progresses with time.
2) the most common is in association with
psoriasis, where the thumbs and big toes are the
most likely to be affected, although the pattern is
not as organised and symmetrical as that seen in
the inherited version
3) The third variant is the individual nail which
develops a pincer deformity.
MACRONYCHIA AND MICRONYCHIA
Macronychia and micronychia are conditions
where a nail is considered too large or too small
in comparison with other nails
The nail disorder is usually associated with an
abnormal digit, arising from underlying bony
abnormalities such as local gigantism causing
macronychia or megadactyly .
Also the basis of racket thumb, the most
common form of benign, dominantly inherited
Anonychia is absence of all or part of one or several
nails. It may be congenital, acquired or transient.
A mutation in the R-spondin 4 gene, which plays a
part in Wnt signalling within the cell is responsible for
congenital absence of nail
Acquired forms are due to scarring of the nail matrix.
This can arise as a result of burns, surgery or
trauma, or be due to inflammatory dermatoses such
as lichen planus where the entire nail matrix is
scarred and lost
The transient variant is due to nail shedding. This can
occur due to an intense physiological or local
ABNORMALITIES OF NAIL ATTACHMENT
Nails may be lost through different
1) Complete loss of the nail plate due
to proximal nail separation extending
distally is called onychomadesis and is a
progression of profound Beau’s lines
2) Local dermatoses, such as the
bullous disorders and paronychia, cause
nail loss e.g. toxic epidermal
necrolysis, lichen planus etc.
3) Trauma is a common cause of
It is often associated with subungual
4) Temporary loss has also been described due to drugs
such as retinoids,cloxacillin and cephaloridine
5) Onychoptosis defluvium or alopecia unguium
describes atraumatic,familial, non-inflammatory nail loss
6) Nail shedding can be part of an inherited structural
defect, most obviously in epidermolysis bullosa
7) Nail degloving this refers to partial or total avulsion
of the nail and surrounding tissue (perionychium).Typically,it
appears as thimble-shaped nail shedding or total loss of the
nail organ with soft tissue
DIFFERENT EXAMPLES OF SEPERATION
OF NAIL ATTACHMENT
Onycholysis is the distal or lateral separation of the
nail from the nail bed
Psoriatic onycholysis can be considered the
reference point for other forms of onycholysis where it
is typically distal, with variable lateral involvement.
Areas of separation appear white or yellow due to air
beneath the nail and sequestered debris, shed
squames and glycoprotein exudate.
Isolated islands of onycholysis present as ‘oily spots’
or ‘salmon patches’ in the nail bed.
This is a painless separation of the nail from its
bed, which occurs without apparent cause.
Overzealous manicure, frequent wetting and
cosmetic ‘solvents’ may be the cause.
The condition usually starts at the tip of one or
more nails and extends to involve the distal third of
the nail bed.
Onycholysis: idiopathic type
Fingernail in psoriasis
Onycholysis due to other causes is secondary
onycholysis. It may be localised or systemic
Psoriasis, fungal infections, dermatitis and trauma are
among the most common. Onycholysis occurs in
general medical conditions, including impaired
peripheral circulation, hypothyroidism
,hyperthyroidism , hyperhidrosis, yellow nail syndrome
and shell nail syndrome
Photo-onycholysis may occur during treatment with
psoralens, demethylchlortetracycline and doxycycline
The term ‘pterygium’ describes the winged appearance
achieved when a central fibrotic band divides a nail
proximally in two.
inflammatory destructive process precedes pterygium
There is fusion between the nail fold and underlying nail bed
The fibrotic band then obstructs normal nail growth.
It most typically develops in trauma or lichen planus and its
variants, including idiopathic atrophy of the nail and graft-
It can also occur in leprosy and secondary purulent infection.
Ventral pterygium or pterygium inversum unguis
occurs on the distal undersurface of the nail
Causes include trauma, systemic sclerosis,Raynaud’s
phenomenon, lupus erythematosus, familial and
entails hyperkeratosis of the nail bed and hyponychium
Nail plate thickening is common. Dry, white or yellow
hyperkeratosis may crumble away from the overhanging nail
Hyperkeratosis may extend onto the digit pulp.
Features of onychomycosis and wart virus infection (mainly
toes) or psoriasis, pityriasis rubra pilaris and eczema
(mainly fingers) are found
The nail bed is an epithelium of low proliferative turnover.
Any disease process that affects it is likely to result in an
excess of squamous debris. The overlying nail prevents
simple loss. The initial outcome is compaction of debris into
layers of subungual hyperkeratosis.
Focal subungual keratoses seen with Darier’s disease, and
keratotic debris beneath the nail in Norwegian (crusted).
CHANGES IN NAIL SURFACE
Longitudinal grooves may run all or part of the
length of the nail in the longitudinal axis
The median canaliform dystrophy of Heller is
the most distinctive form in this
The nail is split, usually in the midline, with a fir-
tree-like appearance of ridges angled
The thumbs are most commonly affected and
the involvement may be symmetrical.
TRANSVERSE GROOVES AND BEAU’S LINES
Transverse grooves may be full or partial
thickness through the nail.
When they are endogenous they have an
arcuate margin matching the lunula.
If exogenous, such as those due to manicure
the margin may match the proximal nail fold
and the grooves may be multiple as in
When the transverse groove’s are due to
endogenous cause, the groove is better
known as beau’s lines
Pitting presents as punctate erosions in the
The individual pits of psoriasis are said to be
An isolated large pit may produce a localized
full thickness defect in the nail plate termed
elkonyxis, which is found in Reiter’s
disease, psoriasis and following trauma
as a rough surface
affecting all of the nail
plate and up to 20 nails
The original French
term was ‘sand-blasted
nails’, which evokes the
main clinical feature of a
grey, roughened surface
mainly associated with
areata, psoriasis and
Onychoschizia is also
known as lamellar
dystrophy and is
transverse splitting into
layers at or near the free
It is seldom associated
with any systemic disorder,
although it has been
(HIV) infection and
CHANGES IN COLOUR
Alteration in nail colour may occur because of changes
affecting the dorsal nail surface, the substance of the nail
plate, the undersurface of the nail or the nail bed.
Exogenous pigment on the upper surface is easy
to demonstrate by scraping the nail. If the
proximal margin of the pigment is an arc
matching the proximal nail fold, this is a further
clue confirming an exogenous source.
NAIL PLATE CHANGES
The nail plate can be changed by the addition of pigment or the
alteration of the normal cellular and intercellular organization such
that there is loss of normal lucency.
Normal Pigment is typically added in the form of melanin
produced by matrix melanocytes during nail formation. This
produces a brown longitudinal streak the entire length of the nail.
The incorporation of heavy metals and some drugs into the nail
via the matrix can also produce altered nail plate colour, such as
the grey colour associated with silver.
The disruption of normal nail plate formation by disease,
chemotherapy, poisons or trauma can result in waves of
parakeratotic nail cells or small splits between cells within the nail.
In fungal infection discoloration may start distolaterally rather than
via the matrix.
NAIL BED CHANGES
Normally there is generalized vascular changes in the
nail bed, but localized changes, as seen with nail bed
Subungual hyperkeratosis or the incorporation of drugs
(antimalarials, phenothiazines) may also change the
apparent colour of the nail.
Splinter haemorrhages, representing ruptured nail bed
vessels, deposit haemoglobin on the undersurface of
the nail, which grows out.
Cyanosis makes the nail bed blue and carbon
monoxide poisoning makes it bright red.
White discoloration of the nail attributable to
matrix dysfunction is known as leukonychia.
In an inherited form called total leukonychia,
all nails are milky porcelain white.
In subtotal leukonychia,
the proximal two-thirds are white, becoming pink
This is attributed to a delay in keratin maturation
Transverse leukonychia (Mees’ line) reflects a
systemic disorder , such as chemotherapy or
In apparent leukonychia,
changes in the nail bed are responsible for the
Nail bed pallor may be a non-specific sign of
anaemia, oedema or vascular impairment.
This is white proximally and normal distally
Seen in cirrhosis, congestive cardiac failure and
adult-onset diabetes mellitus.
Nail bed biopsy reveals only mild changes of
Terry’s nail is similar to half-and-half nails where,
there is a proximal white zone and distal (20–60%)
brownish sharp demarcation,
the histology of half and half nail suggests an increase of
vessel wall thickness and melanin deposition.
seen in 9–50% of patients with chronic renal failure and
MUEHRCKE’S PAIRED WHITE BANDS
These bands are parallel to the lunula in the
nail bed, with pink between two white lines.
They are commonly associated with
the correction of hypoalbuminaemia by
albumin infusion can reverse the sign.
COLOUR CHANGES DUE TO DRUGS
Yellowing of the nail is a
rare occurrence in
therapy, which can also
produce a pattern of dark
YELLOW NAIL SYNDROME
•The nails in yellow nail
syndrome are yellow due to
•a tinge of green suggets
•The lunula is obscured
•increased transverse and
•loss of cuticle
•chronic paronychia with
onycholysis and transverse
ridging may occur
• The condition usually
presents in adults
YELLOW NAIL SYNDROME
An autosomal dominnant inheritance is
lymphoedema at one or more sites may
respiratory or nasal sinus disease may present
Also occur in d-penicillamine therapy and
nephrotic syndrome ,hypothyroidism & AIDS
Attempted treatments include oral and topical
vitamin E, oral zinc
•It is a longitudinal red
streak in the nail
•Forms a strip where the
nail bed is less compressed
by the overlying nail so that
• color is more easily seen
because the nail is thinner
in this line.
•Splinter hemorrhages may
•Seen with lichen planus &
darrier’s disease ,
Describe the isolated, benign warty distal nail
term coined by baran
Can be associated with longitudinal
The papilloma is a secondary element, given
that it is found distally in the nail bed while
the cause lies proximally within the matrix.