General facts about skin :
- Skin is the largest organ in the body,
accounting for 15-20% of total body weight &
covers a surface area of 2 m2.
- Human skin consists of 3 main layers;
- upper epidermis
- middle dermis &
- lower sub-cutaneous tissue
- The epidermis is mainly composed of
keratinocytes and is 0.4-1.5mm in thickness.
It is formed by division of cells in the
basal layer which move outwards forming
upper layers. The cellular progression from
the basal layer to the skin surface takes
about 30 days.
- Melanocytes are cells that distribute
packages of melanin pigment which gives skin
its colour. It is the nature of the melanin
and the size of the cells containing it
rather than the number of melanocyte that
account for the different appearances
between white and black skin.
- The dermis is a supporting matrix with
a remarkable capacity for retaining water.
The thickness of the dermis varies from less
than 0.5 mm to more than 5 mm. There are two
principal types of protein, collagen and
elastic tissue, out of which collagen
comprises 80–85% of the dry weight.
- Skin also contains many supporting
structures like hair follicles,
pilosebaseous unit which secrete oily
substance called sebum
Functions of skin:
- The main function of skin is to
act as a barrier to external
environment which can be
- Permeability barrier to
water
- Barrier to bacteria & other
micro-organisms
- Mechanical barrier
- Barrier to ultraviolet rays
- Regulation of body temperature
achieved through dilation or
constriction of blood vessels or
secretion of sweat by sweat glands
- As sensory organ, helping in
perception of different sensations
- Subcutaneous fat has important
role in cushioning trauma as well as
providing insulation and a calorie
reserve.
