Integumentary System
“The finest clothing made is a person's own skin, but, of course,
society demands something more than this.”
Mark Twain
Case Study
• The brown recluse spider has a venom that
contains an enzyme called phospholipase.
▫ This destroys the phospholipid bilayer that makes
cell membranes.
• The venom liquefies the cells of its prey, allowing
it to feed by sucking in the nutrients.
• Brown recluse spiders
have small chelicerae (fangs),
so the bite doesn’t go deep and
the damage is superficial.
• Enzymes can be re-used over and over again, so
the tissue damage gradually gets deeper,
eventually reaching the blood vessels and muscle
underneath.
Case Study
• The outermost layers of skin exist to
prevent foreign substances from entering
the body.
• The resulting tissue damage
from the bite is highly
prone to infection, as
these outer layers are
broken down.
▫ Infection is the biggest
long-term risk from this
injury.
• The longer the bite is left untreated, the more tissue
damage that occurs, and the greater the risk of infection.
The Integumentary System
• The integument is the largest
organ in the body.
▫ 16% of body weight, 1.5-2m2 in area.
• Consists of two parts:
▫ Cutaneous membrane (skin)
▫ Accessory structures (hairs, glands)
• Functions of the integumentary
system include:
▫ Protection from impact, chemicals,
and infection.
▫ Maintaining body temperature.
▫ Synthesis of vitamin D.
▫ Storage of lipids.
▫ Sensory reception; contains nerve
endings for touch, pressure, pain,
and temperature.
▫ Excretion of fluids like sweat and
milk.
Hair Shaft
Epidermis
Stratified Squamous
Stem Cells
Sebaceous Gland
Arrector Pili Muscle
Dermis
Nerve
Hair Follicle
Nerve
Hypodermis
Subcutaneous
Tissue (Fat Cells)
Merocrine Sweat Gland
Epidermis
• The epidermis is made of
avascular stratified
squamous epithelium.
▫ Avascular means no
blood vessels -- any
nutrients and oxygen must
reach these cells by
diffusion from lower
layers.
• Areas of the body with thick
skin (palms of hands, soles
of feet) have epidermis with
five layers of cells.
▫ Thickness of a paper towel.
• All other areas of the body have thin skin
only have four layers of epidermis.
▫ Thickness of a plastic bag.
Life Cycle in the Epidermis
• Cells of the epidermis pass through five different
stages as they grow and move outward.
• Cells begin at the base
(near the dermis) and
gradually move
towards the outer
surface.
• Each layer is called a
stratum.
• The deepest layer of the
epidermis is called the
stratum basale.
• The stratum basale
contains folds or
papillae that increase
surface area for the
diffusion of nutrients.
• This layer is dominated
by large stem cells that
continuously divide.
• The papillae of the
stratum basale are
responsible for the
formation of the
surface ridges we
observe as
fingerprints on
areas of thick skin.
• The stratum basale also contains melanocytes;
cells that produce the pigment melanin that
colors the epidermis.
Human hand with
uneven distribution of
melanin.
From wisegeek.org
• Stem cells gradually stop
dividing as they reach
the stratum
spinosum.
• At the stratum
granulosum, begin
producing large
amounts of keratin, a
durable and waterresistant protein.
• Keratin is found in many external structures,
including hair, nails, horns, hooves, feathers,
and even the baleen plates of whales.
Lee Richmond’s world record fingernails (8.65m), grown
from 1979-2008. Source: guinnessworldrecords.com.
• The palms of the hands
and soles of the feet have
an additional layer of
clear, keratin-packed
cells in the stratum
lucidum.
• The exposed surface of
the skin, stratum
corneum, is made of
15-30 layers of cells that
have been flattened and
filled with keratin.
• Cells in the stratum corneum are dead; they are
too far away from the deep blood vessels to
receive adequate oxygen and nutrients.
• Cells remain in place for two weeks, connected
to each other by desmosomes.
Dust
• Dust is primarily made of dead cells shed from
the stratum corneum, along with clothing fibers
and dust mite feces.
The Epidermis and Vitamin D
• Ultraviolet light in small doses helps the body
produce Vitamin D.
▫ Essential for the absorption of calcium and
phosphorus by the intestines.
• Excessive doses of ultraviolet light can damage
skin, cause mutations, and increase the risk of
cancer.
▫ Additional melanin can be produced as a
protective measure, creating tanning.