anatomy of nail and applied aspects

ANATOMY & APPLIED ASPECTS OF NAIL

Dr. Yugandar

Hard & Durable Epidermal Appendages

Similar to Claws & Hooves of animals

Covers 1/5th of dorsal surface of the digits (Great

toes upto 30% )

It is difficult to obtain nail producing substance &

grow nails and nail matrix keratinocytes in culture

Mouse nails display amazing homology with human

nails,Mouse models and mouse genomics used for

nail research

Components of Nail

• Nail Matrix• Nail Bed• Cuticle• Nail Plate• Nail Folds• Lunula

Anatomy of the Nail

Lunula: it is visible part of nail matrix,best

seen in thumb,poorly in little finger

Cuticle: the fold of skin tissue at base of the

nail that overlaps lunula & protects nail bed

Nail Matrix:

- It is tissue which is protected by nail

- Contains nerves,lymphatics & blood vessels

- It is responsible for production of nail plate

Nail bed: skin beneath the nail plate Nail plate: it is hard part of nail,made of

translucent keratin protien Distal edge: anterior margin of nail plate Proximal nail fold:- Epithelium with a granular layer- Corresponds to skin of digit- Contains sweat glands

Hyponychium: it is epithelium located beneath nail plate at junction b/w distal edge & skin of fingertip

Eponychium: small band of epithelium from post nail wall onto the base of nail

Paronychium: it is border tissue around nail Perionyx: it is projecting edge of the

eponychium covering the proximal strip of lunula

Nail Matrix differentiation

• As new plate cells formed old cells push forward & compressed become flat, translucent, that makes nail bed capillaries visible pink colour

Direction of differentiation & cell movement with in nail apparatus

Histological section of proximal nail matrix

Histologic section shows dorsal & ventral portions of the proximal nail fold

Proliferating epithelial cells of matrix & ventral aspect of the PNFStaining with antibody MIB-1

Development

Nail apparatus develops & matures from

Primitive epidermis b/w 9th & 20th week of

intrauterine life

First identified at 10th week of IUL as a

primary nail fields of proliferative ectoderm on

tips of terminal segments of digits

Development

Due to slow growth rate,Primary nail fields

become depressed & Epidermis overlaps their

sides & Proximal ends forms nail folds

Proximal part of each nail field forms root of

nail,becomes germinative portion

From germinative portion actual substance of

nail develops

Development

Keratin synthesis identified in early embryonic

differntiation

Fetal growth of nail is gradual,finger nails

appear longer than toe nails,at birth nail

edges reaches tips of digits

Functions of Nail

• Protection• Sensory Perception• Manual Dexterity• Scratching• Picking up small objects• Augments sensation of touch

Blood Supply of Nail

Lateral digital arteries supply nail through

superficial,proximal & distal arcades

Vasculature of nail bed is unique in that it

must supply a vascular structure b/w two hard

surfaces ie nail plate & distal phalanx


Large AV anastomoses with glomusbodies,

play key role in peripheral circulation &

thermoregulation

Glomus bodies called as Peripheral heart of

masson


Vasculature of nail


Capillary microscopy of the proximal nail fold showing longitudinally oriented capillary loops

Nerve Supply of Nail

Nail unit is richly innervated by nerves which are

branches of median,ulnar & radial nerves

Innervation of nail unit is through two laterally

positioned sensory nerves

Digital nerves divides in to three branches just

distal to the interphalangeal joint to supply

different constituents of the nail unit

Nerve supply of nail through branches of Median,Ulnar & Radial nerves

Nail Growth

Nail growth is continuous,it ceases at

death( skin tightens & dehydrates appear nails

grow)

Finger nail grows at rate of 0.1 mm/ day,

3mm/ month

Toe nail grows at rate of 0.033 mm/

day,1mm/month

Nail Growth

It is proliferating cells of germinative matrix

most contributes to nail growth

Thinning of nail plate usually sign of nail

matrix disease,Nail thickening sign of nail bed

disease

Nail Growth

Complete replacement finger nails- 6

months,toe nails-18 months

Nails grow more in summer than other

season

Nail Growth - Physiological factors

Increase : Right hand,Dominant hand,Pregnancy,2nd & 3rd decade,Youth,Fingers,Male upto 19 years

Decrease : At birth,After age 60 yrs,Lacatation,Left hand,Non Dominant hand,Old age,Toes,Females upto 69 yrs,Thumb & Little fingers

Nail Growth - Other Factors

Decrease : Cooler temp,Finger

Paralysis,Hypothyroidism,Fever,Measles,Mumps,

CRF,Pneumonia,TB,Malnutrition,Yellow nail

syndrome,Onychomycosis

Increase : Warm temp,AV shunts,

Hyperthyroidism,Psoriasis,P. Rubra Pilaris,Drugs

( L- Dopa,Retinoids,Itraconazole), Finger Trauma

Reasons : Nails grow always forward & flat

• Guiding restraint of proximal nail fold

• Influence of underlying phalanx

• Adherence of nail plate to nail bed

• Containment by Lateral nail folds

Reasons : Nails Pointed & Rounded

• No Clear reason for it

• Function of Lunula

• Nail bed may have role

• Iso Kikuchi syndrome – Abnormally shaped

Lunula – Hemionychogryphosis

Nails in Childhood & Adults

In Early Child – Nail plate thin & temporary

Koilonychia ( More Prominent Great Toes)

Prominence of nail surface markings –

Herringbone or Chevron Nails

Solitary beau’s lines – Infancy

Nails in Childhood & Adults

Onychophagia,Punctate

Leuconychia,Pitting,Lamellar Splitting of free

edge of nail – normal in children

Elderly – Slow rate of growth

Neapolitan nails : Proximal half – White,No

Lunula,Distal Edge is opaque,Central portion –

Pink.

Nail Composition

• Lamellar sheets of tightly adherent dead

corneocytes containing large amount of

protien ( 78 % ),Small amounts of water ( 18

%),Very Little Lipid ( < 5 % )

Nail Composition

• Hardness due to structural protiens alfa helical

keratin,Cystiene rich amorphous matrix

protien

• Mineral content of nail Zn,Fe,Cu & Mg in small

quantites

Nail Composition

Nail Matrix Dorsal ( undersurface of

proximal nail fold ) Intermediate or germinative Ventral (nail bed

epithelium)

Nail Plate Dorsal lamina : Dorsal

matrix derived Intermediate layer:

Germinative matrix derived Ventral layer: Ventral matrix

derived

Nail Matrix

Nail Matrix KeratinocytesMelanocytesLangerhans cellsMerkel cells

Biochemistry of Nail

• Low sulfur keratins,High sulfur keratins

• High glycine tyrosine matrix protiens

• Presence of K6/K16 keratins in nail bed

demonstrates hyperkeratotic state in diseases

• Mutation in K16 gene observed in

pachyonychia congenita

Keratin gene expression at different locations with in nail

Importance of Nail Composition

• Cystic fibrosis – Na,Cu Elements Increased

• Wilsons disease – Cu increased

• Iron def anemia – Fe decreased

• Acrodermatitis enteropathica – Zn decreased

• Environmental Exposure – As,Pb increased

Importance of Nail Composition

• Cocaine in nail clipping in newborn indicative

of Cocaine exposure during embryogenesis

• X linked Icthyosis – Steroid

sulfatese,Cholesterol sulfatase

Nail signs – Deposition of pigments

Pigmentation from external staining typically

follows shape of proximal nail fold eg: yellow

brown discolouration in smokers d/t

Nicotine,Darkening of nail plate in hairdressers

Metals Gold (Chrysiasis),Silver(Argyria)


Subungual deposition of Green pigment seen

in Pseudomonas colonization d/t

Pyocyanin,Yellow Subungual pigment d/t

Dermatophytes

Exogenous – Convex Proximal Border,

Endogenous – Concave Proximal border,

Subungual deposition- a/w onycholysis


Dermoscopy very useful for assessment of nail

plate pigmentation & nail bed changes

Nail plate in Forensic Medicine

Due to Slow Growth rate of nails makes it

possible to utilize nail clippings to detect

previous exposure to drugs,metals and toxins

eg Heroin,cocaine,amphetamine

Drug exposure,Poisoning,Genetic analysis

Finger nail clippings of victims for

identification of accused by DNA method

Nail plate in General Medicine

Nail clippings used for identification of

Alcohol dehydrogenase enzyme defect in

hepatic dysfunction

Long term control of blood glucose levels in

diabetes

HBV DNA

Nail plate in General Medicine

Creatine levels in renal dysfunction

Porphyrin levels in PC Tarda

Assesment of Environmental exposure to

pollutants eg: Pb,Nicotine

Nail signs as an aid to diagnosis of congenital heart diseases

Correlation of nail findings with anatomic site of nail damage

Applied aspects of Nail

Congenital disorders of nail unit:

Anonychia,Congenital malalignment of bigtoe,

IsoKikuchi syndrome,Micronychia,

Macronychia,

Polyonychia,Onychoheterotopia,Racket

nails,Periodic shedding


Congenital disorders of nail unit:

Dolichonychia,Circumferential nails,Nail

patella syndrome

Alterations in Nail shape: Clubbing,Shell

nails,Racket nails


Alterations in Nail size:

Anonychia,Micronychia,Polyonychia,Nail

patella syndrome,Iso Kikuchi syndrome


Alterations in the Nail Plate: Beau’s

lines,Onychomadesis,Washboard nails,

Koilonychia,Pincer nails,Brittle nails,

Platyonychia,Pitting,Multiple longitudinal nail

grooves,Onychorrhexis,Trachyonychia,20-nail

dystrophy of childhood,Pachyonychia

congenita


Disease of Nail bed:

Trauma – Sportsman’s toe

Primary skin diseases – Psoriasis,Alopecia

Areata,Lichen planus,Dermatitis,Porphyria,

Pachyonychia congenita,Epidermolysis bullosa

Drugs – Retinoids,Doxycycline,

Chemotheraphy,Na Valproate

Chemicals


Systemic – Fe def anemia,Connective tissue diseases,hypo or hyper thyroidism

Infections – Candida,Herpes,Warts,Bacterial Paronychia,Onychomycosis

anatomy of nail and applied aspects

Health & Medicine