Nail is a hardened keratin plates (cornified zone) on the dorsal surface of the tips of fingers and toes, acting as a rigid support for the digital pads of terminal phalanges. They are horn-like envelopes covering the dorsal aspect of terminal phalanges of fingers and toes of human body.
Parts of a nail:
Each nail has the following parts.
- Root: Root is the proximal hidden part which is buried into the nail groove and is overlapped by the nail fold of the skin.
- Free border: Free border is the distal part free from the skin.
- Body: Body is the exposed part of the nail which is adherent to the underlying skin. The proximal part of the body presents a white opaque crescent called lunule. Each lateral border of the nail body is overlapped by a fold of a skin, termed the nail wall.
The skin (germinative zone + corium) beneath the root and body of the nail is called nail bed. The germinative zone of the nail bed beneath the root and lunule is thick and proliferative (germinal matrix), and is responsible for the growth of the nail.
The rest of the nail bed is thin (sterile matrix) over which the growing nail glides. Under the translucent body (except lunule) of the nail, the corium is very vascular. This accounts for their pink color.
Clinical anatomy of nail:
• In anemia the nails are pale and white.
• In iron deficiency anemia the nails become thin, brittle and spoon-shaped (koilonychia).
• Hypertrophy of the nail bed (clubbing) occurs in chronic suppurative disease (lung abscess, bronchiectasis, osteomyelitis) and in severe type of cyanosis (Fallot’s tetralogy, chronic congestive cardiac failure).
• Disturbances of nail growth due to acute illness or trauma give rise to transverse grooves in the nail substance, which move distally with the nail growth. Since the average rate of growth is about 0.1 mm per day or 3 mm per month, the date of the past illness can be estimated.
• It takes about 90-120 days for the whole nail (body) to grow. Therefore, in fungal diseases of the nails the course of treatment should last for not less than this period. The growth is faster in summer than in winter, in the fingers than in toes, and in the longer fingers than in the shorter ones.