This lecture help the students such as medical ,nursing , and any health care provider to understand the basic information about anatomy of skin.

1. THE SKIN
Dr. Luma Alzamel

2. Structure of the skin
The skin has a surface area of about
1.5 to 2 m2 in adults
and it contains glands, hair and
nails. There are two main
layers:
• epidermis
• dermis.
Between the skin and underlying
structures there is a layer of
subcutaneous fat.

4. Epidermis
The epidermis is the most superficial layer of the skin and
is composed of stratified keratinized squamous epithelium
which varies in thickness in different parts of the body. It
is thickest on the palms of the hands and soles of the feet.
There are no blood vessels or nerve endings in the
epidermis, but its deeper layers are bathed in interstitial
fluid from the dermis, which provides oxygen and
nutrients, and is drained away as
lymph.
There are several layers (strata) of cells in the epidermis
which extend from the deepest germinative layer to the
surface stratum corneum (a thick horny layer). The cells
on the surface are flat, thin, non-nucleated, dead cells in
which the cytoplasm has been replaced by the fibrous
protein keratin. These cells are constantly being rubbed
off and replaced by cells which originated in the
germinative layer and have undergone gradual change as
they progressed towards the surface. Complete
replacement of the epidermis takes about 40 days.

5. The maintenance of healthy epidermis depends
upon three processes being synchronized:
The skin showing the main layers of the
epidermis.
• desquamation (shedding) of the keratinized
cells from the surface
• effective keratinization of the cells approaching
the Surface.
• continual cell division in the deeper layers with
newly formed cells being pushed to the surface.
Hairs, secretions from sebaceous glands and ducts
of sweat glands pass through the epidermis to
reach the surface.
The surface of the epidermis is ridged by
projections of cells in the dermis called the
papillae.

6. The color of the skin is affected by three main factors.
• Melanin, a dark pigment derived from the amino
acid tyrosine and secreted by melanocytes in the deep
germinative layer, is absorbed by surrounding
epithelial cells. The amount is genetically determined
and varies between different parts of the body,
between members of the same race and between
races. The number of melanocytes is constant so the
differences in color depend on the amount of melanin
secreted. It protects the skin from the harmful effects
of sunlight. Exposure to sunlight promotes synthesis
of increased amounts of melanin.
• The level of oxygenation of hemoglobin and the
amount of blood circulating in the dermis give the
skin its pink color.
• Bile pigments in blood and carotenes in
subcutaneous fat give the skin a yellowish color.

7. Dermis
The dermis is tough and elastic. It is
formed from connective tissue and the
matrix contains collagen fibers
interlaced with elastic fibers. Rupture of
elastic fibers occurs when the skin is
overstretched, resulting in permanent
striae, or stretch marks, that may be
found in pregnancy and obesity. Collagen
fibers bind water and give the skin its
tensile strength, but as this ability
declines with age, wrinkles develop.
Fibroblasts, macrophages and mast cells
are the main cells found in the dermis.
Underlying its deepest layer there is
areolar tissue and varying amounts of
adipose tissue (fat).

8. The structures in the dermis are:
• blood vessels
• lymph vessels
• sensory (somatic) nerve endings which are
sensitive to touch, change in temperature,
pressure and pain are widely distributed in the
dermis.
• sweat glands and their ducts are found widely
distributed throughout the skin and are most
numerous in the palms of the hands, soles of the
feet, axillae and groins. They are composed of
epithelial cells. Glands opening into hair follicles
do not become active until puberty. In the axilla
they secrete an odorless milky fluid which, if
decomposed by surface microbes, causes an
unpleasant odor. The functions of this secretion
are not known. Sweat glands are
stimulated by sympathetic nerves in response to
raised body temperature and fear.

9. The most important function of sweat
secreted by glands opening on to the skin
surface is in the regulation of body
temperature. Evaporation of sweat from
body surfaces takes heat from the body
and the amount of sweat produced is
governed by the temperature-regulating
center in the hypothalamus. Excessive
sweating may lead to dehydration and
serious depletion of body sodium chloride
unless intake of water and salt is
appropriately increased. After 7 to 10
days' exposure to high environmental
temperatures the amount of salt lost is
substantially reduced but water loss
remains high.
• hairs, arrector pili muscles and
sebaceous glands.

10. Hairs
These are formed by a down-growth of epidermal
cells into the dermis or subcutaneous tissue,
called hair follicles.
At the base of the follicle is a cluster of cells called
the bulb. The hair is formed by multiplication of
cells of the bulb and as they are pushed upwards,
away from them source of nutrition, the cells die
and become keratinized.
The part of the hair above the skin is the shaft
and the remainder, the root.
The color of the hair is genetically determined
and depends on the amount of melanin present.
White hair is the result of the replacement of
melanin by tiny air bubbles.
Accessory organs of the skin

11. Nails
The nails are derived from the
same cells as epidermis and
hair and consist of a hard,
horny keratin plate. They
protect the tips of the fingers
and toes.
The nail plate of the nail is the
exposed part that has grown
out from the germinative zone
of the epidermis called the nail
bed.
Fingernails grow more quickly
than toenails and growth is
quicker when the
environmental temperature is
high.
Subcutaneous gland
Sweat gland

12. Thanks for listing