Integumentary System Includes:
Skin (cutaneous membrane)
Subcutaneous tissue below the skin
Sebaceous or oil glands
Layers Of The Skin
Epidermis – outer
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 identified:
First Layer of the Epidermis
The stratum basale
is the deepest layer of the epidermis (closest to the
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 renewal of the epidermis takes about 3 to 4
weeks in humans as millions of cells are produced
Cells die as they are pushed away from the source
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.
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.
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.
Final Epithelial Layer
Closest to the surface of the epidermis, the stratum
corneum has a somewhat looser appearance.
Cells are constantly shed from this part of the
This layer makes up three fourths of the epidermal
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
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
Melanin protects the chromosomes of
mitotically active basal cells against light-
Pigmentation is not just under the
control of light. Hormones
produced by the pituitary and the
adrenal glands also affect
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 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 hypodermis.
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.
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.
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 animals.
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 temperature.
Ceruminous glands (or ear wax glands) and
mammary glands are modified apocrine sweat
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.
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.
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