An organ consists of a group of tissues that performs
a specific function.
The tissues comprising the skin are the epithelium of
the epidermis and the connective tissues of the dermis.
A system is a group of organs working together
toward common goals.
The organs that make up the integumentary
system are the skin and its derivatives, such as hair,
nails, glands and nerve endings; many interrelated
factors (nutrition, hygiene, circulation, age, immunity,
genetic traits, psychological traits, psychological state
and drug use) affect both appearance and health of the
The skin is one of the largest organs of the body.
Dermatology is the medical specialty that deals
with diagnosing and treating skin disorders.
Structurally, skin consists of two principal parts:
the epidermis (the outer, thinner portion
composed of epithelium) and the inner or thicker
dermis which is composed of connective tissue.
It overlies the subcutaneous or SubQ layer. This
is also called the superficial fascia or hypodermis.
Functions of the Skin
Regulation of body temperature
Synthesis of Vitamin D
The epidermis is composed of stratified
squamous epithelium and contains four
principal types of cells: keratinocytes,
melanocytes, Langerhans cells and Merkel
Four or five (soles or palms) distinct layers
form the epidermis.
The layers of the epidermis (from deepest to
most superficial) are: stratum basale (also
known as the stratum germinitivum),
stratum spinosum, stratum granulosum,
stratum lucidum (which is only in the palms
and soles) and the stratum corneum.
The basale layer undergoes continuous cell
division and produces all other layers.
The cells in the multiple layers of the stratum
corneum are continuously shed and replaced by
the cells from the deeper strata.
Keratinization: replacement of cell contents with
the protein keratin, occurs as the cells move to the
skin surface over 2 to 4 weeks.
Epidermal Growth Factor or EGF is a
hormone that stimulates growth of epithelial
and epidermal cells during tissue
development repair and renewal.
The dermis is composed of connective
tissue containing collagen and elastic fibers.
It has two regions: papillary and reticular
The papillary layer is areolar connective
tissue containing fine elastic fibers, dermal
papillae and corpuscles of touch or
The reticular layer is irregular connective containing
collagen and elastic fibers, adipose tissue, hair follicles,
nerve, sebaceous (oil) glands and ducts of sudoriferous
Strength, extensibility and elasticity are provided to the
skin by the combination of collagen and elastin fibers.
Lamellated or Pacinian corpuscles found in the
subcutaneous layer (hypodermis or superficial fascia) are
sensitive to pressure.
Lines of cleavage (tension lines) indicate the direction of
collagen fibers bundles in the dermis and are considered in
making surgical incisions.
The wide variety of colors in skin are due to
three pigments: melanin, carotene and
hemoglobin (in blood capillaries) in the
The color of skin and mucous membranes
can provide clues for diagnosing certain
problems such as cyanosis, jaundice and
Epidermal ridges increase friction for better
grasping ability and provide for the basis of
fingerprints and footprints. The ridges
typically reflect contours of the underlying
When the germinal portion of the epidermis is
destroyed, new skin cannot regenerate without a
skin graft. The most successful type of skin graft
comes from the individual himself or from an
Another type of self donation is autologous skin
transplantation in which sheets of skin are grown
in the laboratory from a small amount of the
patient’s epidermis, synthetic materials may be
used to simulate dermis and epidermis while this
skin is being grown.
Epidermal derivatives are structures
developed from the embryonic epidermis.
Examples of epidermal derivatives are hair,
skin glands (sebaceous, sudoriferous and
ceruminous) and nails.
Hairs or pili are epidermal growths that function in
protection and reduction in heat loss.
Hair consists of a shaft above the surface, a root that
penetrates the dermis and subcutaneous layer and a hair
Associated with hairs are sebaceous (oil) glands, arrectores
pilorum muscles and root plexuses in a cyclic pattern.
The color of hair is primarily due to melanin.
Hormones—particularly androgens—can stimulate hair
growth in both males and females or somehow inhibit it in
genetically predisposed males (male pattern baldness).
Drug treatment can occasionally stimulate regrowth of
some lost hair.
Sebaceous (oil) glands are usually
connected to hair follicles; they are absent
in the palms and soles.
Sebaceous glands produce sebum which
moistens hairs, waterproofs and softens the
Enlarged sebaceous glands may produce
blackheads, pimples and boils.
Sudoriferous glands or sweat glands are divided
into apocrine and eccrine types.
Eccrine Sweat Glands: have an extensive
distribution, their ducts terminate at pores at the
surfaces of the epidermis.
Apocrine: Limited in distribution to the skin of
the axilla, pubis, and areolae their ducts open into
the hair follicles. Sudoriferous glands produce
perspiration (sweat) which assists in maintaining
proper body temperature and also carries small
amounts of washes to the surface.
Ceruminous glands are modified
sudoriferous glands that produce a waxy
substance called cerumen. The are found in
the external auditory meatus (ear canal).
Nails are hard keratinized epidermal cells over the
dorsal surfaces of the terminal portions of the
fingers and toes.
The principal parts of a nail are: body, free edge,
root, luncuna, eponychium and matrix.
Cell division of the matrix cells produce new
Functionally, nails help in grasping and
manipulating small objects in various ways and
provide protection against trauma to the ends of
Skin and Homeostasis
Epidermal Wound Healing: wounds are
repaired by enlargement and migration of
basal cells, contact inhibition and division
of migrating and stationary basal cells.