Integumentary System
Statistics
Covers the entire body.
 Weighs between 9 to 11 lbs.
 Thickness of skin in some areas can be
from 1.5 to 4 mm thick.
 Flexible yet tough.
 The #1 defense from bacteria and fungi.
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Hypodermis
(Not technically part of the skin)
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A.k.a. Superficial fascia.
Stores fat
Anchors the skin (loosely)
It is important that we understand that the
hypodermis anchors skin down loosely because
it allows some potential trauma to slide off of the
body.
Hypodermis will thicken when we gain weight.
(In women, thighs and breasts first, in men
anterior abdomen)
Hypodermis
Hypodermis anchors skin loosely
Hypodermis thickening
Epidermis
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The epidermis is made up of keritanized
stratified squamous epithelium.
Cell Types: Keratinocytes
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Keratinocytes: cells
that produce keratin.
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Keratin: fibrous
protein that gives skin
its protective
properties.
Cell Types: Melanocytes
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Melanocytes: synthesize melanin. Have a weblike appearance. Found in the deepest part of
the epidermis.
Melanin is created by the melanocytes, shipped
up to the keratinocytes through the spider-like
arms of the melanocyte, and deposited in the
side of the nucleus of the keratinocyte that faces
towards the sun, which creates a barrier that
protects the keratinocyte’s nucleus from UV
damage.
Melanocytes
Cell Types:
Epidermal dendritic cells
A.k.a. Langerhan’s cells
 Spawn from bone marrow and work their
way to the epidermis.
 Key part of the immune system.
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Langerhan’s cells
Cell Types: Tactile cells
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A.k.a. Merkel cells
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Very intimately close
to Merkel discs that
act as receptors for
the touch sense.
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Merkel cell carinoma 
Layers of the epidermis
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Number of layers vary based on whether
skin is thick or thin.
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Thick: 5 layers
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Thin: 4 layers
Thick Skin
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Thick skin’s 5 layers:
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Examples of thick skin
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Stratum basale
Stratum spinosum
Stratum granulosum
Stratum lucidum
Stratum corneum
Covers palms of hands
Fingertips
Feet
*Stratum= layer
*Strata= layers
Thin skin
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Thin skin’s 4 layers:
Stratum basale
 Stratum spinosum
 Stratum granulosum
 Stratum corneum
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Examples of thin skin:
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Everywhere else
Stratum Basale
A.k.a. Basal layer
 Deepest layer and attached to the dermis.
 As these cells divide, they push the cells
above them closer to the surface of the
skin, and force the other layers to mature
into fully formed keratinocytes faster.
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Stratum spinosum
Several layers thick. Contains a web-like
system of intermediate filament designed
to resist tension.
 Looks like prickly spiked balls.
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Stratum granulosum
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Thin layer (3-5 layers).
This is where the bulk of keratinization occurs.
Each of the layers in this stratum will start to look
very different.
Cells flatten; nuclei and organelles disintegrate.
Forms lamented and keratohyaline cells.
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Keratohyaline cells: helps form keratine in the upper
layers
Lamented cells: creates water resistant glycolipids
that fill extracellular spaces in the cell.
Stratum lucidum
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Consists of two clear flat dead cell layers.
Uses keratin to bind together in a cable
like array. (thick skin only)
Stratum corneum
Outermost layer. (20-30 cell layers thick)
 Mostly all the cells of this layer are dead.
Designed to be durable and take
damaged. Seen most often flaking off as
dandruff.
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End of Epidermis
Dermis
Second major skin region. Made of strong
connective tissue.
 Contains connective tissue proper cell
types:
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Fibroblasts
 Macrophages
 Few mast cells
 Few white blood cells
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Major layers of the dermis
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Papillary layer:
Made of areolar connective tissue.
 Contains interwoven elastic and collagen
fibers.
 Contains heavy amounts of blood vessels.
 The loose connections of the tissue allows
free movement of defensive cells, like the
WBCs and macrophages.
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continued
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The superior surface contains peg-like projections
called dermal papillae. Others contain free nerve
endings (pain receptors) and touch receptors
called Meissner’s corpuscules.
On the hands and feet, papillae lay on ridges
called dermal ridges. The dermal ridges have
ridges on top of them called epidermal ridges.
These ridges of skin are collectively called friction
ridges.
Since sweat pores open on these crests, we will
leave behind a small film of sweat on anything we
touch. You know these as fingerprints.
Reticular layer
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The deeper and thicker of the two layers.
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Course, irregular cell arrangement, dense
fibrous connective tissue.
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The cutaneous plexus, a layer of blood
vessels that give nutrients to this layer, are
between this layer and the hypodermis.
continued
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In certain areas, skin that has less dense
regions of the collagen fibers will form
what is called cleavage.
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When surgeons make an incision parallel
to these lines, the skin gapes less and
heals faster.
continued
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Flexure lines are dermal folds that occur
near joints where the dermis is firmly
anchored to deeper structures. (look at the
creases on the palms of your hands)
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The dermis is folded due to the fact that
skin cannot slide enough to conform to the
joints in your hands.
End of Dermis
Skin Color
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Three major pigments make up the skin:
Melanin
 Carotene
 Hemoglobin
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Melanin
Only one of the three pigments made in
the skin.
 Polymer of tyrosine amino acids.
 Passed up from melanocytes to
keratinocytes.
 Found only in the deepest layers
of the epidermis.
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Melanin
Human skin color
Skin tone:
 Darker skinned people are distributed
more around the equator. This is due to
more direct contact from the sun’s rays.
 Their skin produces more melanin to
protect their skin cells from harmful UV
rays.
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Carotene
Yellow-orange pigment found in certain
plants like carrots. Accumulates in the
stratum corneum, and in fatty layers of the
hypodermis.
 In asian people, the yellowish tint to their
skin is due to varying levels of melanin
and carotene.
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Carotene
Hemoglobin
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The pinkish hue of hemoglobin is most
evident in Caucasian people due to the
fact that they lack very much pigment,
allowing the reddish tint of hemoglobin to
shine through the skin.
Heme group
End of skin color
Glands
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Appendages (added attachment) of the
skin, glands function to cool down the
body and expel wastes.
Sudoriferous Sweat Glands
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All over the skin’s surface with the
exception of the nipples and part of the
external genitalia.
There can be upwards of 3 million of these
glands on a body.
 When myoepithelial cells contract, they
squeeze out the secretion and forces the
sweat to the skin surface.
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Eccrine sweat glands
A.k.a. merocrine sweat glands.
 Most abundant on the palms of the hands,
forehead, and soles of the feet.
 The secretory part is deep in the dermis,
and pores (channels) allow for secretions
to be brought to the surface.
 The secretion from eccrine glands are
what we call sweat.
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Contains small amounts of uric acid (also
found in urine), which alters the pH of
sweat to between 4-6.
 Major role is to prevent overheating of the
body.
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Apocrine glands
Confined to the axillary (under arm) and
anogential (genital region) areas.
 Begin functioning around puberty.
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Ceriminous glands
Modified apocrine glands.
 Secrete sebum in the ear canal.
 Mix with sebacous glands to form ear wax.
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Mammary glands
Secrete milk.
 Also included as a part of the female
reproductive system.
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Oil based glands
Sebaceous Glands (oil glands)
Branched alveolar glands. Found
everywhere except the thick skinned parts
of the hands and feet.
 Most are found in hair follicles.
 gland store oils, and become so stuffed
with oil, it explodes! (holocrine gland)
 Lipids plus cell fragments= sebum
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What happens when sebaceous
glands become clogged up?
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If a sebaceous gland becomes clogged
with sebum, the a whitehead may form.
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If that material oxidizes and dries, then a
blackhead is formed.
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The inflammation of the sebaceous gland
along with a pustule or cyst is called acne.
End glands
Hair
Hair covers almost all of the body.
 Functions to keep us warm and help us
sense insects before they bite us.
 Hair on the head guards against physical
trauma, heat loss, and sunlight.
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Examples of hair
Hair structure
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Pili (hair) consists
largely of dead
keratinized cells.
Hard keratin
prominent in hair.
Allows hair to be
tougher and more
durable, and
individual cells do not
flake off.
Hair anatomy
Consists of a shaft, and a root. The root is
the active growing region.
 Flat and ribbon like hair structure results in
kinky hair.
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If the follicle is round, then the hair will
appear wavy.
Hair
Contains three keratinized layers of cells.
 Middle layer called the medulla, consists
of large cells and spaces.
 The cortex surrounds the medulla, and
consists of several layers of flattened cells.
 The cuticle is the outermost layer that
forms by having a single layer of cells
overlap each other like shingles on a roof.
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Hair root
The root of the hair contains the hair bulb,
which is beneath the skin’s surface.
 The hair bulb has a sensory nerve ending
wrapped it called the hair follicle receptor,
which allows transmissions of messages
to the brain when a stimulus is applied.
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Hair follicle
Wall is composed of connective tissue root
sheath, which is derived (came from)
dermal tissue.
 This is an invagination
in the epidermis formed
by the inner root sheath.
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The arrector pilli
A muscle associated with the hair follicle.
 Most hairs grow in at an angle. The
arrector pilli pull hairs into an upright
position.
 When the body cools too low, the arrector
pilli is responsible for creating bumps on
the skin surface.
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Not very useful in humans because we
have short hairs, but in long haired
animals it allows them to retain heat.
Types of Hair
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Vellus hair- thin hair. Mostly on children
and adult females.
Types of Hair
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Terminal hair-Longer thicker hair, found on
eyebrows and scalp.
Growth Rates of Hair
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Varies , but the greatests rates of hair
growth occur on the scalp and armpits.
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The hair on the legs can be stimulated by
shaving, due to a physiological response
to the cold. (Even when it is hot)
Growth of hair is the fastest between your
teens through your 40’s.
 Male pattern baldness is a genetic sexlinked trait, and doesn’t just “happen”.
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End hair
Nails
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Scale like modification to hands.
Protective covering for the fingers, allows
us to pry open objects.
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Nails correspond to claws and hooves in
other animals.
The Nail bed
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In the nail bed, the thickened portion is
called the nail matrix. The nail matrix is
the place where the nail grows.
Anatomical terms for the nail
Nail folds- lateral parts of the nail that the
skin folds over.
 Eponychium- the nail body (cuticle)
 Hyponchium- below the nail.
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End Nails
Functions of the Integumentary
system
Protection
 Body temperature regulation
 Cutaneous sensation
 Metabolic function
 Blood reservoir
 Excretion
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Protection
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Chemical barriers: i.e. melanin in the skin.
The acid mantle, due to a lower pH of the skin,
the skin tends to ward off or slow down most
bacterial growth.
Skin produces an antibiotic called defensins,
which fight off microbial growth.
Cathelicidians- wounded skin produces a
multitude of peptides called cathelicidians, which
fight off bacteria (especially streptococcus)
Physical barriers
Provides a physical continuity to skin.
Thicker skin could be beneficial, but we
would lose softness and agility.
 Glycolipids in the epidermis prevent
diffusion directly through the skin.
Prevents water loss and water entry in the
skin.
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Biological barriers
Includes DNA, macrophages on the
dermis and dendritic cells of the epidermis.
 Electrons in DNA can absorb UV rays to a
degree, which allows for DNA to resist
some of sun the sun’s rays.
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Body Temperature Regulation
Under normal conditions, the body will
lose 0.5L of sweat per day.
 When your body temperature rises, your
nervous system sends a signal to your
sweat glands to begin perspiration.
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Cutaneous sensation
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Cutaneous sensory receptors (part of the
nervous system). Allows us to sense
when there is a change in the
environment, like the wind blowing.
Metabolic functions
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The skin uses a modified form of
cholesterol, along with the sun’s rays, to
create a vitamin D precursor to ultimately
create vitamin D.
Blood reservoirs
The skin can hold up to 5% of the body’s
blood.
 When the blood vessels constrict, excess
blood may be forced out of the blood
vessels and into the skin, making you look
flushed.
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Excretion
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Ammonia and uric acid are removed from
the body through sweat.
End Functions
Imbalances in the skin
(Bad stuff)
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Skin cancer- damage to the p53 gene,
which is a tumor supressing gene. Usually
requires frequent dermal irritation.
(frequent tanning, sun burn)
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Basal cell carcinoma- appears shiny and
dome shaped. Accounts for 80% of all
skin cancers. Sun exposed areas usually
where lesions occur. Relatively slow
growth. Unlikely to metastasize.
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Squamous cell carcinoma-grows rapidly
and has a higher metastasis rate. Usually
scaly and red, slightly raised.
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Melanoma- cancer of melanocytes.
Usually appears as an irregular black
patch.
Know your ABCD’s
A. Asymmetry- the sides of the mystery
mole do not match.
 B. Border irregularity- borders of mole
have indentations
 C. Color- contains blacks, browns, blues,
and other colors.
 D. Diameter- spot is larger than 6 mm in
diameter.
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Burns
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1st degree- least severe. Only epidermis is
damaged.
Burns
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2nd degree-damage to the epidermis and
the upper layers of the dermis. Slim
chance of infection. Really hurts!
Burns
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3rd degree- Severe damage to epidermis,
dermis and even parts of the hypodermis.
Skin must be removed. Does not hurt.
Things burn victims need to worry
about
Over heating
 Limited mobility
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