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Skin is the largest organ
of the body and is
the mirror of one’s personality. It is the barrier against the
environmental insults and prevents loss of water from the body. Skin has important
role in regulation of body
temperature, perception, synthesis of vitamin
D and social communication. We have to understand
our skin to not only understand the problems of the skin, but also to
adjust to the surrounding environment and to communicate with our fellow
humans.
Skin is the mirror of one's
personality...
Skin is a constantly
renewing tissue and consists of three layers – the epidermis, dermis and the
subcutaneous tissue.
The epidermis is made up of
keratinocytes and melanocytes. The keratinocytes are
arranged in layers and the
top-most layer is called the stratum corneum. This layer is
made up of dead cells which are continuously shed. Lower most
layer of the epidermis is called stratum germinatum. Cells
in this layer divide constantly and give rise to daughter cells that
replace the old cells in the stratum corneum. The process of daughter
cells maturing and moving to the top layer is called
keratinization (cell cycle). This process occurs constantly and
continuously and the duration of this cell cycle is 26-42 days. The end
product of this process is the stratum corneum. Stratum corneum
maintains the water content in the skin. It is an effective barrier to
trans-epidermal water loss and to penetration of exogenous substances.
When the process of keratinization is disturbed either by disease
(genetic or acquired), environmental factors or ageing, the barrier
becomes defective. A defective stratum corneum leads to flaking of the skin
due to increased trans-epidermal water loss, increased incidence of
irritant/allergic dermatitis due to easy entry of obnoxious agents,
increased incidence of UV radiation induced changes such as light
eruption, pigmentation and growths.
Melanocytes
are pigment (melanin) producing cells present in the lower most layer of
the epidermis. They produce melanin and disperse it to the neighbouring
keratinocytes. Melanin pigment gives colour to the skin and the hair and
protects the skin from the sunlight. Each melanocyte is in connection
with 32 neighbouring keratinocytes (epidermal melanin unit). Any defect
in the process of synthesis and dispersion of the pigment leads to hyper
(dark) or hypo (light) pigmentation.
Beneath the epidermis is the layer called
dermis. It is made up of ground substance like hyaluronic acid
and dermatan sulfate as well as fibres like elastin and collagen that are responsible
for the elasticity of the skin. When the collagen and elastin in the dermis get
damaged with age, the skin shows wrinkles.
The dermis has three types of
glands: the apocrine, eccrine and sebaceous glands. The
apocrine glands
are found in association with hair follicles, abundantly in the arm
pits. They are responsible for the body odour. The eccrine glands are
distributed widely over the body; they produce sweat and help in
regulation of the body temperature. Normally the sweat is odourless, but
colonisation of certain bacteria may impart it a bad odour. The sebaceous glands are
present
throughout the skin except the palms and soles and are numerous on the
scalp and the face. These glands secrete an oily substance called
sebum, which lubricates the skin and forms a coating on the hair,
keeping it soft and shiny. When the sebum secretion is inadequate, the
skin becomes dry and wrinkled and when the secretion is increased, the
skin becomes oily and shiny.
In addition to this,
the dermis contains a network of blood vessels, lymphatics, nerves
and cells of the immune system.
Subcutaneous tissue
comprises of fat globules and largely supports the overlying dermis and
epidermis.
Hair is essentially a vestigial structure
that man has
lost during evolution. However, any change in the pattern, quality, quantity or colour of
the hair causes a tremendous concern, out of proportion to its
physiologic function.
Each hair undergoes a
cyclic growth in three phases:
- The growth phase - 3-4
years
- Followed by catagen
- 10 days
- Followed by telogen
(resting) - 2-3 months
During the resting
phase the hair becomes detached from its root and falls out as a new
growing hair replaces it in the follicle.
On an average, the scalp
contains 100,000 hair. At any given time 10-15% of the scalp hair are in
inactive phase, ready to fall out, while the remaining are in various
stages of growth. A loss of up to 100 hairs per day is normal and is
something one should not worry about as most of the lost hair would be
replaced. With age, however, the rate of replacement slows down; so as you
grow older, there is a natural tendency for some amount of sparseness of
your scalp hair.
The rate of hair growth
varies considerably, but on an average it is one cm per month and is
more in summer than winter. Growth rate is maximum between 15-30 years.
Cutting or shaving does not make the hair grow faster. Neither does trimming
affect the growth rate in any way, though it does make you look good by
eliminating straggling ends.
Good quality long hair
runs in families and so does the male type baldness. A good balanced
diet is a must for good growth and texture of hair.
Nails
protect the tips of the fingers. The nail unit is composed of nail
plate, nail matrix, nail bed and nail folds. The nail plate is
surrounded on three sides by the nail fold, the invaginations of
the epidermis that provide a guiding groove for nail growth. Cuticle is
that part of the nail unit which is between the nail fold and the nail.
It helps to seal the matrix and the soft nail from the outside. Nail
matrix is a specialised epidermis that produces the nail. As the nail
matrix cells differentiate, they keratinise (become hard) and produce
the nail plate. The rate of growth of the nail plate is approximately 0.1mm per
day.
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