The Integumentary System
Integumentary System Includes:
Skin (cutaneous membrane)
Subcutaneous tissue below the skin
Sebaceous or oil glands
Layers Of The Skin
Epidermis – outer
composed of stratified
Dermis – inner
anchored to a
Composed of stratified squamous
Avascular as it has no blood supply of its
Oxygen and nutrients diffuse from the
The epidermis is a keratinized stratified
squamous epithelium. Oxygen and nutrients
diffuse from the underlying dermis. Five
structurally different layers can be
First Layer of the Epidermis
The stratum basale
is the deepest layer of the epidermis (closest to the dermis).
It is found close to the dermal blood supply. It consists of a
single layer of columnar or cuboidal cells which rest on the
basement membrane. Basal cells are the stem cells of the
epidermis. Their mitotic activity replenishes the cells in more
superficial layers as these are eventually shed from the
epidermis. The renewal of the epidermis takes about 3 to 4
weeks in humans as millions of cells are produced daily.
Cells die as they are pushed away from the source of
nourishment. Cells undergo keratinization as a tough
protein, keratin, is deposited within the cell. Keratin hardens
and flattens the cells as they move outward and it
waterproofs the skin.
Optional Epidermal Layers
In the stratum spinosum,
the cells become irregularly polygonal. The cells are often
separated by narrow, translucent clefts. These clefts are
spanned by spine-like cytoplasmatic extensions of the cells
(hence the name of the layer and of its cells: spinous cells),
which interconnect the cells of this layer.
The stratum granulosum
consists, in thick skin, of a few layers of flattened cells. Only
one layer may be visible in thin skin.
The stratum lucidum
consists of several layers of flattened dead cells. Nuclei
already begin to degenerate in the outer part of the stratum
granulosum. In the stratum lucidum, faint nuclear outlines
are visible in only a few of the cells. The stratum lucidum
can usually not be identified in thin skin.
Final Epithelial Layer
In the stratum corneum,
cells are keratinized and form a layer that is about
30 cells thick. Individual cells are difficult to
observe because (1) nuclei can no longer be
identified, (2) the cells are very flat and (3) the
space between the cells has been filled with lipids,
which cement the cells together into a continuous
membrane. Closest to the surface of the epidermis,
the stratum corneum has a somewhat looser
appearance. Cells are constantly shed from this
part of the stratum corneum. This layer makes up
three fourths of the epidermal thickness. The
protection of the body by the epidermis is due to
the functional features of the stratum corneum.
Dermis or corium
The dermis, or corium, consists of dense
fibrous connective tissue with numerous
collagenous and elastic fibers. The dermis is
much thicker than the epidermis. In thick skin,
dermal papillae create a very irregular border
between epidermis and dermis. Blood vessels,
nervous tissue, some muscle tissue, certain
glands, hair and nails are found in the dermis.
Nerve endings allow us to sense pain,
temperature, pressure, and touch.
Red and Yellow, Black and White…
The red and yellow hues of the skin are due to hemoglobin in
the red blood cells, which pass through the capillaries beneath
the epidermis, and carotene (yellowish pigment), which
accumulates in fat cells found in the dermis and hypodermis
(subcutaneous layer beneath dermis).
The brown in skin color is due to melanin, which is produced in
the skin itself in cells called melanocytes. These cells are
located in the epidermis. In the melanocytes, the melanin is
located in membrane-bound organelles called melanosomes.
Melanocytes can transfer melanin to keratinocytes - mainly to
the basal cells. Melanin protects the chromosomes of mitotically
active basal cells against light-induced damage.
Pigmentation is not just under the control of light. Hormones
produced by the pituitary and the adrenal glands also affect
pigmentation. Diseases of these two endocrine organs often
result in changes of pigmentation of the skin.
Albinism – melanocytes completely fail to secrete
melanin. Hair, skin, and iris are white.
Vitiligo – loss of pigment in certain areas of the
skin producing white patches.
Freckles and moles are formed when melanin
becomes concentrated in local areas.
Malignant melanoma – a cancerous change in a
mole that may metastasize (spread) rapidly and is
most difficult to treat. Exposure to sunlight
Other Pigments in Skin
Carotene – a yellow pigment in skin usually hidden by
the effects of melanin. Asians have little melanin
which allows the yellow to show more than other
Pinkish color – seen in fair-skinned persons because
the vascular dermis is visible.
Cyanosis – blue look to skin due to poorly oxygenated
Blushing – caused by dilation of blood vessels
Pale by fright – caused by restriction of vessels
Response to Disease
Jaundice – caused when bilirubin is deposited in
skin because a diseased liver is unable to excrete
Skin may appear bronzed due to the deposit of
excess melanin when a person’s adrenal gland is
A bruise indicates that blood has escaped from the
blood vessels and has clotted under the skin.
Over eating carotene-rich vegetables such as
carrots may cause skin to have a yellow tint.
Accessory Structures of the Skin
A characteristic feature of the human skin is the
apparent lack of hair on most of the body surface.
This is actually not quite true. Most of the skin is
haired although the hair in most areas is short, fine
and only lightly pigmented.
Truly hairless are only the palms of hands and soles
of feet, the distal phalanges and sides of fingers and
toes and parts of the external genitalia.
Accessory Structures of the Skin
In those parts of the skin which we perceive as "hairy" we
find terminal hairs. The free part of each hair is called the
The root of each hair is anchored in a tubular invagination
of the epidermis, the hair follicle, which extends down
into the dermis and, usually, a short distance into the
The hair that you groom daily is actually dead keratinized
Each hair follicle has an associated bundle of smooth
muscle, the arrector pili muscle. This muscle inserts with
one end to the papillary layer of the dermis and with the
other end to the dermal sheath of the hair follicle. This
makes your hair stand up on its end.
Accessory Structures of the Skin
Hair Color and Texture
Hair color is determined by the amount and type of
Melanocytes become less active with age. Gray hair is
a mixture of pigmented and non-pigmented hairs.
Red hair results from a a modified type of melanin that
The shape of the hair shaft determines texture.
Round shaft – straight hair
Oval shaft – wavy hair
Flat shafts – curly or kinky hair
Perms use chemicals to flatten shafts and makes hair curly.
Alopecia is the term for hair loss.
Accessory Structures of the Skin
Plates of stratified squamous epithelial cells
with hard keratin
Protect distal ends of phalanges
Cells are keratinized in the nail root
Nail growth occurs in the lunula
Cuticle is a fold of stratum corneum on the
proximal end of nail
Sebaceous glands or oil glands are simple branched
areolar glands. They secrete the sebum (seb = oil) an
oily product. Sebum is usually secreted into a hair
follicle. Sebum is a natural skin cream: it helps hair
from becoming brittle, prevents excessive evaporation
of water from the skin, keeps the skin soft and contains
a bactericidal agent that inhibits the growth of certain
Sebaceous glands are scattered all over the surface of
the skin except in the palms, soles and the side of the
Vernix caseosa - white covering on fetus.
Sweat glands or sudoriferous glands are simple coiled tubular
glands. They are divided into two principal types: eccrine and
Apocrine glands are found mainly in the skin of the armpits, of
the anogenital areas and of the areola of the breasts. Their secretory
portion can be located in the dermis or in the hypodermis. Their
excretory ducts open into hair follicles. Their secretion is more
viscous than that of the eccrine glands. They start secreting at
puberty and may be analogous to the sexual scent glands of other
Eccrine glands are the most common. Their secretory portion can
be located in the dermis or in the hypodermis. They produce sweat,
a watery mixture of salts, antibodies and metabolic wastes. Sweat
prevents overheating of the body and thus helps regulate body
Ceruminous glands (or ear wax glands) and mammary glands
are modified apocrine sweat glands.
Physiology of the Skin
Protection - the epidermis provides a barrier to
fluid loss from the body (this protective function is
impaired in patients with burns).
barrier function - intact skin prevents the entry of
micro-organisms into the body. Antimicrobial
proteins are produced by the epidermis - they act by
piercing holes in the outer membranes of micro-
Resistance to wear and tear - continuous replacement
of the outer epidermal cells that wear off - new cells
are produced in the deepest layer of the epidermis and
gradually migrate towards the surface
Skin can excrete water, salt, and small amounts
of waste products such as urea.
Vitamin D can be synthesized in skin exposed
to sunlight (vitamin D can also be obtained
from the diet)
The skin provides a barrier to ultraviolet light.
The melanocytes contain melanin, which
absorbs UV radiation, and also distribute the
pigment to neighboring cells. Skin exposed to
sunlight becomes wrinkled and creased.
Changes seem to be due to disruption of
collagen and elastin in dermis, and loss of
fibroblasts which make new proteins.
Three types of skin cancer corresponding to three major
types of skin cells: basal cells, squamous cells, and
Cancer of melanocytes - malignant melanoma - is the
most lethal variety, but also the least common.
If caught early, most cases of non-melanoma skin
cancer are easily treated under local anaesthetic
Whites in Australia have the highest rates of skin cancer
of all types in the world.
The damaging effects of sunlight can occur many years
before tumors appear.
ultraviolet light causes mutations at points on a DNA
The integumentary system is well-supplied with
receptors for touch, pain, temperature, vibration
Sensory information is relayed to the central
nervous system via sensory nerves
Social interactions are influenced by facial
expressions, blushing, touching, etc.
Skin Diseases and Ailments
House dust is mainly skin flakes!
If you laid out all your skin on a flat surface, it would have
an area of about 2 square meters.
Skin weighs about 2.5 kilograms - the largest organ in the
What hurts if you pull it, but doesn't hurt if you cut it?
Your hair, of course!
Skin is elastic - it springs back into shape when stretched.
Some medicines (estrogen, nicotine) can pass through the
skin, but others cannot (insulin). Why is that? Because
only fat-soluble substances can enter the skin, not water-
Your hair stands on end and you develop 'goose bumps'
because there are tiny muscles attached to the hair follicles
and they contract when you are frightened or cold.