Chapter 5
Integumentary
System
Lecture 5a - Skin Structure
Integumentary system
• Includes the skin, sweat and oil
glands, hairs, and nails
• Major Function – protection
• Accounts for about 7% of total
body weight in the average adult
– (9-11 pounds)
Skin Structure
Figure 5.1
Skin
Structure
• Two layers
• 1. Epidermis outermost layer
– Epi = upon
– Stratified squamous epithelium
– Often keratinized (hardened by
keratin)
Skin Structure
• Two layers
• 2. Dermis
– Dense connective tissue
• Only Dermis is vascularized
• Nutrients reach the epidermis by
diffusion
Hypodermis
• Subcutaneous tissue
– Just deep to skin
• Not considered part of skin
– Functions as a shock absorber and
insulates - Prevents heat loss
from body
• Mostly adipose tissue (so it
stores fat)
Hypodermis
• The hypodermis thickens during
weight gain
– In females, the hypodermis
first thickens in thighs and
breasts
Hypodermis
– In males, the hypodermis first
thickens in the anterior
abdomen - Sometimes
described as a ‘beer belly’
Hypodermis
• Loosely anchors skin to
underlying structures (mostly
muscles)
– Skin is loose enough to slide
somewhat over
structures –
many blows
glance off
our bodies.
Epidermis
• Composed of keratinized stratified
squamous epithelium
• Consists of four distinct cell types
and four or five layers
• Outer portion of the skin is
exposed to the external
environment and functions in
protection
Cells of the Epidermis
• Most are Keratinocytes – produce
the fibrous protein keratin
• Keratin gives the epidermis
protective properties
– Kera = horn in Greek
• Connected by desmosomes
• Keratinocytes arise from the
deepest layer of epidermis whose
cells undergo continual mitosis
• Cells are pushed
upward by the
production of new cells
underneath
• When keratinocytes
reach surface they are
dead, scalelike
structures filled with
keratin
• Millions of these dead cells rub off
daily
– We have a totally new epidermis
every 25 to 45 days
• Persistent friction
causes accelerated
cell and keratin
production and a
thickening of the
epidermis called a
callus
• Melanocytes – spider-shaped cells
that produce the brown pigment
melanin (Melan = black)
• As melanin is made it accumulates
in the processes (the arms) of the
melanocytes cells.
• Then they are taken up by the
keratinocytes and accumulate on
the superficial side of the
keratinocyte nucleus
– Forms a pigment shield to protect
nucleus from ultraviolet radiation
in sunlight
Other Cells of the Epidermis
• Langerhans’ cells – star-shaped cells
that arise from bone marrow and
migrate to the epidermis as epidermal
macrophages that help activate the
immune system
• Merkel cells – function as touch
receptors in association with sensory
nerve endings
Layers of the Epidermis
Figure 5.2b
Layers of the Epidermis
• Thick skin
– 5 layers or strata
(strata = sheets)
– Covers palms, fingertips, soles of
feet
• Thin skin
– 4 layers
Layers of the Epidermis:
Stratum Basale (Basal Layer)
• Deepest epidermal layer firmly
attached to the dermis
• It is a single row consisting of mostly
young keratinocytes, with 10-25%
melanocytes, and an occasional Merkel
cell
• Cells undergo rapid division, (mitosis)
hence its alternate name, stratum
germinativum
Figure 5.2b
Layers of the Epidermis:
Stratum Spinosum (Prickly Layer)
• Several cell layers thick
• Cells contain a weblike system of
intermediate filaments attached to
desmosomes
• Melanin granules and Langerhans’
cells are abundant in this layer
Figure 5.2b
Layers of the Epidermis:
Stratum Granulosum (Granular Layer)
• Thin; three to five cell layers in
which drastic changes in
keratinocyte appearance occurs
– Cells flatten, nuclei & organelles
disintegrate, and keratohyaline
and lamellated granules
accumulate
Layers of the Epidermis:
Stratum Basale
(Basal Layer)
Figure 5.2b
Layers of the Epidermis:
Stratum Lucidum (Clear Layer)
• Present only in thick skin
• Thin, transparent band superficial
to the stratum granulosum
• Consists of a few rows of flat, dead
keratinocytes
Layers of the Epidermis:
Stratum Corneum
• Outermost layer of keratinized cells
• Accounts for three quarters of the
epidermal thickness
• Functions include:
– Waterproofing
– Protection from abrasion and penetration
– Rendering the body relatively insensitive
to biological, chemical, and physical
assaults
• Average person
sheds 40 pounds
of skin flakes
from the
stratum
corneum layer in
a lifetime
– Provides food
for dust
mites!
Dermis
• Second major skin region containing
strong, flexible connective tissue
• Cell types include fibroblasts,
macrophages, and occasionally mast cells
and white blood cells
• Composed of two layers –
papillary and reticular
Dermis
• Richly supplied with nerve fibers, blood
vessels, and lymphatic vessels.
• Most hair follicles, oil and sweat glands
are derived from epidermal tissue but
reside in the dermis
• In animals, this is the
hide that makes leather
products
Layers of the Dermis:
Papillary Layer
• Areolar connective tissue with collagen
and elastic fibers and blood vessels
Layers of the Dermis:
Papillary Layer
• Its superior surface contains peglike
projections called dermal papillae
Layers of the Dermis:
Papillary Layer
• Dermal papillae
contain capillary
loops, touch
receptors called
Meissner’s
corpuscles, and
free nerve endings
• On palms of the hands and soles of
the feet, dermal papillae lie on top
larger mounds called dermal ridges
• The epidermis that lies on the
dermal ridges is called the
epidermal ridges
• These epidermal ridges are
genetically determined and unique
to each of us
• These are our fingerprints!
Layers of the Dermis:
Reticular Layer
• Accounts for approximately 80% of the
thickness of the dermis
• Is dense irregular connective tissue
• Collagen fibers in this layer add
strength and resiliency to the skin
• Elastin fibers provide stretch-recoil
properties
• Most bundles of collagen fibers run
parallel to the skin surface.
• Less dense regions of collagen fibers
form cleavage or tension lines in the
skin – invisible from surface
• These cleavage lines are important to
surgeons
– Incisions made parallel to these lines,
the skin gapes less and heals more
readily than when the incision is made
across cleavage lines
• Epidermal ridges (fingerprints) and
cleavage lines are called skin markings
• Another type of skin marking is
Flexure lines
• These are externally visible
• Dermal folds that occur at
or near joints
• See them as creases in your palms,
wrists, finges, soles, and toes
Homeostatic imbalances
• Stretching of the skin can tear the
dermis
– Indicated by silvery white scars
called striae (streaks) commonly
called stretch marks
Homeostatic imbalances
• Stretching orTrauma like a burn or a
poor fitting shoe, or digging a hole
with a shovel, can cause a blister
– Separation of the epidermal and
dermal layers by a fluid filled pocket
Skin Color
• Three pigments contribute to skin color
– Melanin – yellow to reddish-brown to black
pigment, responsible for dark skin colors
• Freckles and pigmented moles –
result from local accumulations of
melanin
– Carotene – yellow to orange pigment, most
obvious in the palms and soles of the feet
– Hemoglobin – reddish pigment responsible
for the pinkish hue of the skin
Melanin
• Made in melanocytes and passed to
keratinocytes
• All humans have about the same number
of melanocytes
– Individual differences in skin coloring
reflect the amount of melanin made and
retained
– Darker skinned people produce more
melanin and their keratinocytes retain it
longer
Melanin
• Melanocytes are more active when
exposed to sunlight
– Protects DNA of skin cells from
UV radiation by absorbing the light
and dissipating the
energy as heat
– Causes a ‘tan’
• Even with Melanin’s protection, excess
sun exposure eventually damages the
skin
• Leathery
skin,
depressed
immune
system,
skin
cancer
Carotene and hemoglobin
• Carotene – yellow to orange pigment
(also found in carrots)
– Accumulates in the stratum corneum and
the hypodermis
– Most intense when carotene-rich foods are
eaten
• Hemoglobin – pinkish hue reflecting the
crimson color of oxygenated hemoglobin
in red blood cells in the dermal
capillaries
Homeostatic imbalances
• When hemoglobin is poorly
oxygenated, both the blood and the
skin appear blue
– Called cyanosis (cyan = dark blue)
– Lots of melanin may mask
cyanotic appearance so darkskinned individuals will only show
blue tint in their mucous
membranes and nail beds
Homeostatic imbalances
• Skin often becomes cyanotic during
heart failure and severe
respiratory disorders
Homeostatic imbalances
• Alterations in skin color signal certain
diseases and emotional stimuli
• Redness – may indicate embarrassment,
fever, hypertension, inflammation, or
allergy
Homeostatic imbalances
• Jaundice or yellow cast – usually
signifies a liver disorder
Homeostatic imbalances
• Bronzing – a bronze or almost metallic
appearance of the skin is a sign of
Addison’s disease
• Black and Blue marks or
bruises – reveal where
blood escaped from the
circulatory system and
clotted beneath the skin
–
called hematomas
We will quiz over
this next time!
Do study Guide pages 101-105
(they will be checked)