THE DERMIS AND ACCESSORY
STRUCTURES
Skin Pigment
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The color of your skin is due to an interaction
between:
(1) epidermal pigmentation
(2) dermal circulation
Epidermal Pigmentation
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Two pigments present in the epidermis:
(1) Carotene – orange-yellow pigment found in the
stratum corneum layer and in the fatty tissues in the
dermis.
(2) Melanin – brown, yellow-brown, or black
pigment produced by melanocytes
Melanocytes
*Melanocytes produce the
pigment melanin. Melanin is
transferred up through the
layers via vesicles called
melanosomes until they are
destroyed.
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In individuals with pale skin, the melanosomes are destroyed
in the lower layers of the epidermis, and the cells of the
more superficial layers lose their pigmentation.
In individuals with dark skin, the melanosomes are larger
and the melanosomes are destroyed in the stratum
granulosum layer, making the pigment in the upper layers
darker.
Melanocytes
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Melanin pigment in your
skin protects you from UV
radiation. Long amount of
UV radiation can damage
DNA, causing mutations
and promoting the
development of cancer. In
the keratinocytes, melanin
is concentrated around the
nucleus, thereby protecting
your DNA from UV
exposure.
Melanocytes
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Although melanocytes increase
their activity and pigment
production when exposed to UV
radiation, the response is not
rapid enough to prevent
sunburn the first day of constant
exposure. Melanocyte activity
peaks about 10 days after
initial exposure.
Chronic exposure to UV
radiation can result in
premature wrinkling, leathery
consistency to skin, and skin
cancers.
Dermal Circulation
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Blood contains red blood
cells that contain the pigment
hemoglobin, that binds and
transports oxygen throughout
the body. Hemoglobin is
bright red. If blood vessels
are dilated, the red tones
seen in light colored
individuals gives the skin a
redder tone.
Cyanosis (blue skin) can
occur due to a sudden drop
in blood supply to the skin.
Epidermis and Vitamin D3
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When exposed to small
amounts of UV radiation,
epidermal cells in the stratum
basale and stratum spinosum
convert a cholesterol-related
steroid into vitamin D3
(choleciferol). The liver then
converts choleciferol into the
hormone calcitriol, essential
for the absorption of calcium
and phosphorus by the small
intestine. An inadequate
supply of calcitriol leads to
impaired bone maintenance
and growth.
The Dermis
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Two major components:
(1) a superficial dermal papillary layer
(2) a deeper reticular layer
Papillary Layer
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Consists of areolar tissue, and contains capillaries
and sensory neurons that supply the surface of the
skin.
Reticular Layer
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Found beneath
the papillary
layer and consists
of dense
irregular tissue.
Bundles of
collagen fibers
extend beyond
the reticular layer
into the
hypodermis
below.
Wrinkles and Stretch Marks
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Although collagen fibers are strong and resist
stretching, they are easily bent or twisted. Elastic
fibers permit stretching but then return to their
original length. Aging, hormones, and UV radiation
exposure reduce the amount of elastin in the dermis,
producing wrinkles and sagging skin.
Decreased skin turgor, and a
sign of dehydration.
Stretch Marks
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Distortion of the dermis
over the abdomen during
pregnancy of after
substantial weight gain
can exceed the elastic
capabilities of the skin.
The resulting damage
prevents it from recoiling
to its original size after
delivery or weight loss.
The skin wrinkles/creases,
creating stretch marks.
Lines of Cleavage
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Most of the collagen and elastic fibers are
arranged in parallel bundles. These
bundles are aligned in different directions
to resist applied forces. The pattern of
arrangement of these bundles are called
lines of cleavage.
These lines are significant, because a cut
parallel to a cleavage line will remain
closed, whereas a cut at right angles to the
line will be pulled open.
Surgeons chose their incision lines based on
the lines of cleavage.
Dermis Layer – Sensory Receptors
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Contains many sensory
receptors:
(1) sensitive to light touch
(Meissner’s corpuscles) that
are located in the dermal
papillae
(2) receptors sensitive to
deep pressure and
vibration (Pacinian
corpuscles)
Accessory Structures - Hair
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Hairs are produced from organs called hair follicles.
Accessory Structures – Types of Hair
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Lanugo – extremely fine, unpigmented hairs that form
after three months of embryonic development
Lanugo is shed before birth and is replaced by:
(1) Vellus hairs – fine peach fuzz located throughout the
body. Puberty causes some vellus hairs to transition to
terminal (airpit, groin, etc)
(2) Terminal hairs – heavy, deeply pigmented, sometimes
curly hairs (head hair, eyebrows, and eyelashes)
Function of Hair
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Head hair protects scalp from
UV radiation and insulates the
head
Nasal hairs prevent entry of
foreign particles into airway
(eyelashes perform same
function for eyes)
A Root hair plexus of sensory
nerves allows you to feel even
slight movements of each hair
shaft
Arrector Pili
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Ribbons of smooth muscle called arrector pili
muscles pull on the hair follicles and force the hair
to stand erect.
Hair Growth Cycle
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Hairs grow and shed based on hair growth cycle. A
scalp hair grows for 2-5 years, at a rate of about 0.33
mm/day
Collections of hair can be useful to assay for:
(1) lead poisoning
(2) arsenic poisoning
(3) heavy metal poisoning
Healthy adults lose about 50 hairs/day from your head.
In males, changing sex hormone level can change
terminal hair to vellus hair, in a process called male
pattern baldness.
Glands
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Two types of exocrine glands:
(1) Sebaceous glands
(2) Sweat glands – consists of
apocrine and ecrine glands
Sebaceous Glands
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Sebaceous glands are oil
glands that discharge a
waxy, oily secretion into
hair follicles
Release sebum (lipids) that
inhibit bacterial growth,
lubricate keratin
(hair/nails), and condition
the skin
Sebaceous Glands
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During the last months of
fetal development, the
sebaceous glands are
extremely active and
produce secretions to form
a protective layer called
the vernix casoesea
Apocrine Sweat Glands
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Located in the armpits,
around the nipples, and in
the groin attached to
hairs
Produce sticky, cloudy,
sometimes odorous
secretions
The sweat is a nutrient
source for bacteria, which
intensify the odor
Begin secreting at
puberty
Merocrine/Ecrine Sweat Glands
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More numerous and
widely dispersed than
sebaceous glands
Palms and soles have
greatest number
Discharge secretions
directly onto skin
Merocrine/Ecrine Sweat Glands
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Function to:
1. Cool the skin through evaporative cooling
2. Excrete water and electrolytes
3. Provide protection to environmental hazards, by
diluting harmful chemicals and discouraging growth
of bacteria
Ceruminous Glands
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Modified sweat glands in
the passageway of the
external ear canal
Secretions are called
cerumen, or earwax
Works along with tiny hairs
to trap foreign particles
and prevent them from
reaching the eardrum
Nails
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Form on the dorsal
surfaces of fingers and
toes
Function to protect
exposed tips of fingers
and toes, and limit their
distortion when
subjected to mechanical
stress, like grabbing
objects
Nails
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Nail production occurs at the nail root
Underlying blood vessels provide nail its color
Small white/pale colored moon called the lunula
found at the base of the nail
Nails – Indication of Health
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Can be used to indicate general
overall health of an individual
EX: yellow nails in individuals
with chronic respiratory
disorders, thyroid disorders, or
AIDS
Pitted nails as a result of
psoriasis
Concave nails as a result of
some blood disorders