Nail Parts and Structure
Nail Parts and Structure
Parts of the Nail and Pictures – Human Finger and
Toe
The human nail is a plate of keratin that lies on the tips of the fingers and toes.
The main purpose of the nails are to protect the fingers and toes, however, the
fingernail also assists with certain physical activities in daily life.
The human nail is
constantly growing and being removed by clipping or biting. In childhood, it
takes the nail about 3
months to grow out completely while this may take up to 6 months in the elderly.
Like any part or organ of
the human body, the condition of the fingernails and toenails are
dependent on the general health status. Therefore changes and defects in the
nails may be indicative of certain systemic diseases.
While the word ‘nail’ is
used to describe the nail bed, the entire human nail involves many other parts,
some of which are not visible from the exterior.
Parts of the Nail
Nail Matrix
The matrix is the source of
the cells that become the keratinized layers of the nail plate. It is located
deep in the nail sinus. As new cells grow, it pushes out the nail plate
replacing it with new keratin at the proximal part of the nail plate that lies
adjacent to the matrix.
Poor circulation,
inadequate nutrition and localized or systemic diseases can affect the growth
of the new cells to make up the nail plate.
Nail
Bed
The nail bed lies
underneath most of the nail plate and is a continuation of the skin around the
nail. It contributes to the keratin of the nail plate although it is to a
lesser degree than the matrix. Blood in the dermal capillaries of the nail bed
give the nail its characteristic light pink color.
Nail
Plate
This the largest part of
the nail and is composed of laminated layers of keratin. It is similar in
structure to human hair and skin and is made up of dead cells.
The proximal edge of the
nail plate is the nail root which emanates from the nail sinus. It extends
across the fingers and toes to protrude from the tip (depending on the length).
This free end of the nail is also known as the distal edge, while the sides are
known as the lateral edges.
The nail plate is smooth
and curved and light pink in color due to underlying dermal capillaries in the
nail bed. Changes in the nail color may be linked to various diseases which are
discussed under Discolored Nails.
At times, ridges, lines,
changes in thickness and discoloration may arise as a result of disease. This
is discussed further under Fingernail Ridges.
Non-pathlogical changes of
the nail plate, include :
1.
longitudinal lines or
ridges which occurs with age.
2.
beading, which is the loss
of the smooth curved surface of the nail plate, may normally occur with age
although severe beading may be indicative of disease.
3.
white dots, specks or lines
on the nail plate (striae leukonychia) is a sign of airspaces within the nail
plate and is not related to a calcium deficiency.
Nail Folds
1.
The nail folds surround and
supports the nail plate on
all 3 sides. It is the junction of the skin and nail plate and may sometimes be
slightly darker in color thereby forming a clearly demarcated margin from the
surrounding skin.
2.
The proximal fold lies over
the nail root and matrix. The lateral nail folds extend from the proximal folds
and runs alongside the nail plate to terminate near the tip of the finger or
toe.
3.
The most distal part of the
lateral nail fold is often prone to trauma from mechanical injury, nail biting
and ingrown nails as well as bacterial and fungal infections. Inflammation and
swelling of the folds is known as paronychia.
Nail Cuticle
1.
Also known as the
eponychium, it is the part of the skin that overlaps onto the proximal part of
the nail plate. It provides
some, although minor, support for the nail plate but more importantly, the
cuticle seals the nail sinus to prevent injury and infection of the nail root
or matrix.
2.
The cuticle is usually
thin, translucent and extends a short distance over the lunula or nail bed. It
has neat margins. Ragged cuticles or uneven cuticles may be the sign of
excessive manicuring, poor nail care with overuse of the hands or it can be a
sign of certain connective tissue diseases.
Nail Lunula
1. This is the crescent shaped area at the base of the
nail plate and is usually pale white to light pink in color. It is an extension
of matrix and if most evident on the thumb. A lunula with a pointy tip is
possibly a sign of excessive manicuring.
Skin Structure and function
The
structure of the skin
The skin is
a very important organ. It is a waterproof barrier over the surface of your
body, it keeps out infection, it protects the delicate tissues underneath and
it can repair itself if it is damaged.
In homeostasis, the skin plays a very important part in maintaining the
body temperature within narrow limits. It is important both for losing heat
when your core temperature goes up and for conserving heat if your core
temperature starts to fall. The structure of the skin is very well adapted to
its function in temperature control.
Structure
of the skin
Layers
of the skin
The epidermis is
on the outside. This has a basal layer which is always forming new cells
through cell division so the epidermis is made up from layers of cells. The new
cells gradually move towards the surface, which takes 1-2 months. As they move up
they gradually die, become flattened and develop keratin. The outermost layer
of the epidermis is made of flat dead cells which are continually worn away by
friction. The keratin and
oil from the sebaceous glands help
to make the skin waterproof.
·
Connective tissue - packs and binds the other structures in the skin.
·
Elastic fibres - make the skin stretchy and resilient.
·
Sensory cells - these respond to sense touch, pressure, heat, cold and
pain.
·
Nerve fibres - to activate muscles and glands and relay messages from
the sensory cells to the brain.
·
Pigment cells which produce melanin - a very dark pigment.
·
Sebaceous glands -
produce oil to keep hair follicle free from dust and bacteria, and to help to
waterproof the skin.
The subcutaneous layer is
the final layer of the skin. This is a layer of fat found in the lower part of
the dermis and underneath it. The thickness of this layer varies depending on
the place in the body and from person to person. A store of fat is useful to
the body as insulation and it can be used for energy when the intake of
nutrients is insufficient.
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