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Chapter 4
The Integumentary system
Functions of the Integumentary
System
Sensory Interface: the skin is the interface between the outside
World and the internal milieu. Therefore, it communicates
intricately with the nervous system to ensure the body maintains
homeostasis.
The skin contains many sensory receptors
responsible for detecting temperature, pressure, pain etc.
protection: cushions & insulates deeper body organs, protects from
bumps, scrapes, chemicals & invading organisms.
Epidermis is water proof (reduce loss or gain of water)
Body temp. regulation: capillary networks & sweat glands regulate
heat loss.
Excretion: excretes urea, salts, water
Produces vitamin D: epidermal cells use UV to create this vitamin
which is necessary for Ca+2 absorption.
Skin is one huge sensory organ! It is
responsible for sending information to the
brain to protect the body from injury.
Note the
difference
between the
epidermis and the
dermis
Watch “Skin” segment National Geographic youtube 5min 40sec
Components of Skin
• Outer Epidermis
:
– epithelial tissue
• stratified squamous keratinized
• Inner Dermis
:
– connective tissue
• loose and dense
Cutaneous Membrane
Epidermis
Dermis
• Protects dermis from
trauma, chemicals
• Controls skin permeability,
prevents water loss
• Prevents entry of
pathogens
• Synthesizes vitamin D3
• Sensory receptors detect
touch, pressure, pain, and
temperature
• Coordinates immune
response to pathogens
and skin cancers
Papillary Layer
Reticular Layer
• Nourishes and
supports
epidermis
• Restricts spread of
pathogens
penetrating epidermis
• Stores lipid reserves
• Attaches skin to deeper
tissues
• Sensory receptors
detect touch, pressure,
pain, vibration, and
temperature
• Blood vessels assist in
thermoregulation
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Components of Skin
• Outer Epidermis
:
– epithelial tissue
• stratified squamous keratinized
• Inner Dermis
:
– connective tissue
• loose and dense
Accessory Structures
Hair Follicles
Exocrine Glands
Nails
• Produce hairs that
protect skull
• Produce hairs that
provide delicate
touch sensations
on general body
surface
• Assist in
thermoregulation
• Protect and
support tips
of fingers and
toes
• Excrete wastes
• Lubricate
epidermis
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Layers of Skin
Epidermis
(five layers)
Surface
Characteristics
Stratum
corneum
• Multiple layers of flattened, dead, interlocking
keratinocytes
• Typically relatively dry
• Water resistant but not waterproof
• Permits slow water loss by insensible perspiration
Stratum
lucidum
• Appears as a glassy layer in thick
skin only
Stratum
• Keratinocytes produce keratohyalin and keratin
granulosum • Keratin fibers develop as cells become thinner
and flatter
• Gradually the cell membranes thicken, the
organelles disintegrate, and the cells die
Basal lamina
Epidermis of thick skin
Stratum
spinosum
• Keratinocytes are bound together by maculae
adherens attached to tonofibrils of the cytoskeleton
• Some keratinocytes divide in this layer
• Langerhans cells and melanocytes are often present
Stratum
basale
• Deepest, basal layer
• Attachment to basal lamina
• Contains epidermal stem cells, melanocytes,
and Merkel cells
Dermis
LM × 225
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Capillary loop of
subpapillary
plexus
Cutaneous
Membrane
Epidermis
Dermis
Papillary layer
Reticular layer
Subcutaneous layer
(hypodermis)
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Dermal Papilla & Epidermal Ridge
Epidermis
Epidermal
ridge
Dermal
papilla
Dermis
Types of Epidermis
• Thin skin :
–Covers most of the body
– This skin is also hairy skin for the
most part
–Has only a few layers of dead surface
cells
• Thick skin :
– Covers the palms
of the feet
of the hands and soles
–Has many layersof dead surface cells
Figure 4.5
The Epidermal Ridges of Thick Skin
Pores of sweat
gland ducts
Epidermal
ridge
SEM × 25
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Stratum Basale & Melanocytes
Melanocytes
in stratum
basale
Melanin
pigment
Basal lamina
Thin skin
LM  600
This micrograph indicates the
location and orientation of
melanocytes in the stratum
basale of a dark-skinned person.
Melanosome
Keratinocyte
Melanin
pigment
Melanocyte
Basal
lamina
Melanocytes produce and store melanin.
Melanocytes & UV radiation
Stratum spinosum
This slide used a special stain so you can see the
Langerhan’s cells.
Stratum granulosum
-
Thin skin vs thick skin
Types of Epidermis
• Thin skin :
–Covers most of the body
– This skin is also hairy skin for the
most part
–Has only a few layers of dead surface
cells
• Thick skin :
– Covers the palms
of the feet
of the hands and soles
–Has many layersof dead surface cells
Major Cell Types of the Epidermis
• Keratinocytes –:the most abundant cells
in the epidermis
– synthesize and secrete keratin(a waxy hydrophobic
protein that creates a water barrier)
– responsible for the “keratinized”epithelium
fibrous structural proteins. Keratin is the key structural material making up the outer layer of
human skin. It is also the key structural component of hair and nails.
Keratin monomers assemble into bundles to form intermediate filaments, which are tough and
insoluble and form strong unmineralized tissues
Melanocytes : – secrete the pigment melanin
• protects the keratinocytefrom the sun
Langerhans and dendritic cells
– antigen-presenting cells
response (a type of macrophage)
– decrease in # with a sun tan!
for the immune
:
Layers of the Epidermis and the Life Cycle
of the Keratinocyteas it moves towards the
surface:
Layers:
cornified
lucid
granular
spiny
basal
Layer of Epithelium
Epidermis (epithilial tissue)
1. stratum corneum
2. stratum lucidum – only palms and
soles – “clear”
3. stratum granulosum
4. stratum spinosom
5. stratum basale
The Basal Layer meets the underlying
Dermis
• Epidermal ridges
(e.g.,fingerprints)
• Dermal papillae (tiny
mounds):
–strengthen
attachment between
epidermis and dermis
Basal Layer
• Contains the stem cells
for keratinocytes
– 1 layer thick
– also contains melanocytes
– This is where mitosis
occurs (about every 15-30 days)
• (psoriasis = ↑mitotic activity
(turnover every 7 days)
– Cells are attached
to
thebasement
membrane (by adherens
junctions)
• hence the name of this layer
Melanocytes
Basal layer
1.
Stratum Basale- Also called germinativum because it’s the “germ” layer.
Germ= reproduction
New cells- active mitosis 15-30 days to go from bottom to top
Melanocytes: produce melanin (several forms: yellow, red, brown & black)
a) Function of melanin: block UVB radiation, protects cells from DNA damage & UV
radiation can break down folic acid (B vitamin) so melanin also prevents breakdown of
folic acid.
B) Exposure to radiation stimulates melanocytes to produce more melanin= tanning.
c) Albinism – no production of melanin
d) Other factors involved in skin color:
carotene – yellow
blood – red
blue skin – cyanotic – lack of oxygen in the blood (cold or dead)
Merkel cells – sensory cells detect pressure
Skin Color
• Skin color depends on:
– the pigments carotene
:
• Orange-yellow pigment
• Found in orange vegetables
• Accumulates in epidermal cells and fatty tissuesof the dermis
• Can be converted to vitamin A
– and
melanin
:
• Yellow-brown or black pigment
• Produced by melanocytes in the basal layer
• Transferred to keratinocytes
• Protects DNA in nuclei of keratinocytes from sun (UV) damage
– and blood
circulation (red blood cells)
• Oxygenated red blood contributes to skin color:
– blood vessels dilate from heat, skin reddens
– blood flow decreases, skin pales
More facts about skin color
• With a tan
–pre-existing melanin darkens
–the rate of new melanin synthesis increases
Illness and Skin Color
• Jaundice :
– buildup of bileproduced by liver
– yellow color
• Cyanosis :
– Bluish skin tint
– Caused by severe reduction in blood flow or
oxygenation
• Vitiligo :
– loss of melanocytes
– loss of color
Stratum spinosum
Spiny Layer
• Contains 2–10 layers of
keratinocytes attached to each
other by many
adherens junctions
• As the cells move away
from the basal layer, they
– begin to shrink
• further from source of nutrition
– are still connected to
adjacent cells by adhering
junctions
– these connections look like
spines
• hence the name of this
layer
Stratum Spinosum
Thickest layer
Contains Langerhan’s cells
Stratum granulosum
Granular Layer
• Contains 2-5 layers of
keratinocytes
• By this point in their life
cycle, keratinocytes are
producing significant
amounts of keratin
– which accumulates in and
around the cells
– they now take on a
granular appearance
• hence the name of this
layer
• The cells are now far
enough away from the source of
nutrition that they are
dehydrating and flatteningas well
Stratum lucidum
Lucid Layer
• The clear (or “lucid”,
hence the name of this layer)
layer
• Contains 1-5 layers of
dying keratinocytes
• The cells are now very
flat so it is difficult to see
individual cells
• The cytoplasm appears
homogeneous all the major
organelles have died and
degenerated
Stratum corneum
Cornified Layer
• Contains 10 -100’s of
layers of dead cells
– depending on whether
thick or thin skin
• Basically composed
of flat sheets (scales) of
keratin
• Layers slough off
• (desquamate) here
Dermis
• Source of blood and
nutrients for the
epidermis
• Composed of 2 layers:
– “papillary”layer:
• loose connective tissue
– “reticular”layer:
• dense irregular connective
tissue
• Directs the characteristics
of the epidermis
Dermis
A. Overall Features
1. thick in some areas, thinner in others
2. contains blood supply, nerves, glands, hair follicles
B. Papillary Layer (Region) – upper 20%
1. loose areolar connective tissue - much "elastin"
2. dermal papillae cause ridges in the epidermis superficially
3. Meissner's corpuscles - sense organ for deep touch
4. small capillaries supply O + nutrients (papillary plexus)
C. Reticular Layer (Region)
1. dense, irregular connective tissue "collagen"
2. collagen fibers interlace in net-like fashion
3. contains: adipose, hair follicle, nerves, glands
4. subcutaneous layer attaches skin to tissue below
a. Paccinian corpuscles - sense pressure change
DERMIS
Figure 4.7a The Structure of the
Dermis and the Subcutaneous Layer
Capillary loop of
subpapillary plexus
Dermal papillae
Epidermal
ridges
*
Fi
*
Papillary layer
Papillary layer of dermis
Reticular layer
Subpapillary
plexus
SEM × 649
a The papillary layer of the dermis consists
of loose connective tissue that contains
numerous blood vessels (not visible), fibers
(Fi), and macrophages (not visible). Open
spaces, such as those marked by asterisks,
would be filled with fluid ground substance.
Cutaneous plexus
Lymphatic vessel
Adipocytes
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Capillary loop of
subpapillary plexus
Dermal papillae
Epidermal
ridges
Papillary layer
Reticular layer
Subpapillary
plexus
Cutaneous plexus
Lymphatic vessel
Adipocytes
Reticular layer of dermis
SEM × 1340
b The reticular layer of the dermis contains
dense, irregular connective tissue.
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Capillary loop of
subpapillary plexus
Dermal papillae
Epidermal
ridges
Papillary layer
Reticular layer
Subpapillary
plexus
Cutaneous plexus
Lymphatic vessel
Adipocytes
Subcutaneous layer
c
SEM × 268
The subcutaneous layer contains large
numbers of adipocytes in a framework of
loose connective tissue fibers.
© 2015 Pearson Education, Inc.
The Hypodermis
• AKA subcutaneous tissue
or superficial fascia:
– NOT a part of the “skin”
– Deep to the dermis
– Composed of loose
connective tissue (primarily
fat)
– Location of hypodermic
injections
Accessory Structures
• Originate in the
dermis
• Extend through
the epidermis to
skin surface:
–hair
–nails
–exocrine glands
• sweat
• sebaceous
The sensory receptors in the skin are:
cutaneous mechanoreceptors
Ruffini's end organ (sustained pressure)
Meissner's corpuscle (changes in texture, slow vibrations)
Pacinian corpuscle (deep pressure, fast vibrations)
Merkel's disc (sustained touch and pressure)
Free nerve endings (light touch)
Thermoreceptor (temperature)
Nociceptor (noxious sensations)
Chemoreceptor (sensitivity to chemicals)
• Functions:
– protects and
insulates
– associated with
touch receptors
Hair
• Composed of dead cells
that are heavily
keratinized
• Hair color is produced by
melanocytes at the hair
papilla
• Associated with:
– Arrector pili:
• smooth muscle
• causes hairs to stand up
producing “goose bumps”
– Sebaceous glands
https://youtu.be/aLY4EzDXwSM
Exposed shaft
of hair
Hair shaft
Sebaceous
gland
Boundary
between hair
shaft and
hair root
Arrector
pili muscle
Hair
root
Connective
tissue
sheath
Hair bulb
Hair papilla
a A diagrammatic view of
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Pearson
Education,
Inc.
single
hair
follicle.
Hair follicle,
cross section
Arrector pili
muscle
Epidermis
Sebaceous
gland
Dermis
Hair
Subcutaneous
adipose tissue
Cortex
Hair bulb
Medulla
Hair papilla
Scalp, sectional view
LM × 66
b A light micrograph showing the
sectional appearance of the skin of
the scalp. Note the abundance of hair
follicles and the way they extend into
the dermis and hypodermis.
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Figure 4.10a Hair Follicles
Hair
Hair Structure
The medulla, or core,
of the hair contains a
flexible soft keratin.
The cortex contains thick layers
of hard keratin, which give the
hair its stiffness.
Sebaceous
gland
Arrector
pili muscle
Connective
tissue sheath
Root hair
plexus
a A longitudinal section and a cross section through a hair follicle
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The cuticle, although
thin, is very tough, and
it contains hard keratin.
Hair follicle structures
Direction
of growth
Free edge
Lateral
nail fold
Nail
Lunula
Eponychium
Proximal
nail fold
a View from the surface
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A Hair Shaft
External layer
Internal layer
Interesting hair facts
• Hairs grow discontinuously
–There are periods of growth and periods of
rest
•Scalp:
– growth periods may last many years
– rest periods average 3 months
• Hair in different regions of the body grows
at different rates
Nails and Nail Production
•Nails protect fingers
and toes :
– composed of dead
cells packed with keratin
– metabolic disorders
can change nail structure
• Nail production
occurs in a deep
epidermal fold near
the bone called the
nail root
Hair
• Medulla – soft keratin – flexible
• Cortex – hard keratin – rigid
• Cuticle – thin, tough outer layer of hard
keratin
Interesting nail facts
• Transparency of the
nail provides a useful
window re amount of
oxygen in the blood!
–Indicator used during
surgery
• No nail polish!
Glands of the Skin
• Sebaceous – secrete oil directly into hair shaft – hairy
areas
• Sweat glands – two types: merocrine and apocrine.
Both are myoepithelial
– Merocrine also called eccrine
• Most numerous in palms and soles
• Common sweat gland
• Used for thermoregulation and excretion of toxins
– Apocrine
• Release their secretions into hair follicles in the armpits, around
the nipples and groin areas
• Others: mammary and ceruminous (ear wax)
Exocrine Glands
consist of
• Assist in thermoregulation
• Excrete wastes
• Lubricate epidermis
Sweat Glands
Sebaceous Glands
• Produce watery solution by
merocrine secretion
• Flush epidermal surface
• Perform other special functions
• Secrete oily lipid (sebum) that
coats hair shaft and epidermis
• Provide lubrication and
antibacterial action
Sebaceous Glands
Sebaceous Follicles
Secrete into hair follicles
Secrete onto skin surface
Apocrine Sweat Glands
• Limited distribution
(axillae, groin, nipples)
• Produce a viscous
secretion of complex
composition
• Possible function in
communication
• Strongly influenced by
hormones
• Merocrine secretion
mechanism
• Widespread
• Produce thin secretions,
mostly water
• Controlled primarily by
nervous system
• Important in thermoregulation
and excretion
• Some antibacterial action
special apocrine glands
Ceruminous Glands
Mammary Glands
Secrete waxy cerumen
into external ear canal
Apocrine glands
specialized for milk
production
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Merocrine Sweat Glands
Sebaceous Glands and Follicles (2 of 2)
Lumen (hair
removed)
Wall of
hair follicle
Basal lamina
Discharge of
sebum
Lumen
Breakdown of
cell membranes
Mitosis and
growth
Sebaceous
gland
Germinative
cells
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LM × 150
Myoepithelial cell
Connective
tissue of dermis
Sweat pore
Duct
Apocrine
gland cells
Lumen
LM × 440
a
Duct of
apocrine
sweat gland
Sectional plane
through apocrine
sweat gland
Apocrine sweat glands
are found in the axillae
(armpits), groin, and
nipples. They produce a
thick, potentially
odorous fluid.
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Cross section
of merocrine
sweat gland
The Skin during the Aging Process
Fewer Active
Follicles
Fewer Active
Melanocytes
• Pale skin
• Reduced
tolerance for
sun exposure
Thinner, sparse
hairs
Reduced Skin
Repair
Skin repairs
proceed
more slowly.
Decreased
Immunity
The number of dendritic cells
decreases to about 50 percent
of levels seen at maturity
(roughly age 21).
Thin Epidermis
• Slow repairs
• Decreased vitamin
D production
• Reduced number
of Langerhans cells
Reduced Sweat
Gland Activity
Tendency to
overheat
Changes in Distribution
of Fat and Hair
Due to reductions in
sex hormone levels
Dry
Epidermis
Reduction in
sebaceous and
sweat gland
activity
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Reduced Blood Supply
Thin Dermis
• Slow healing
• Reduced ability to
lose heat
Sagging and
wrinkling
due to
fiber loss
Skin Cancer Facts
• 1/3 of all tumors are of the skin
• Rarely lethal (deadly) if diagnosed early:
–Basal cell carcinoma: easily curable
• derived from cells in the basal layer
–Squamouscell carcinoma:
• derived from cells in the spiny layer
• Most serious and invasive tumors:
–(Malignant) melanoma:
• derived from melanocytes
Any condition resulting in hair loss is called alopecia
• Actinic Keratosis: Precursor to Squamous
Cell Carcinoma
• Rough, red or pink scaly patches on sunexposed areas of the skin,usually <0.5cm in
diameter
• Precurser lesion for squamous cell carcinoma
(Squamous Cell Carcinoma)
• Up to 1% of these lesions can develop into a
Squamous Cell Carcinoma
Ref:http://www.dermatology.ucsf.edu/skincancer/professionals/types.aspx
• Basal Cell Carcinoma :
• Raised, pink, waxy bumps that may bleed
following minor injury
• May have superficial blood vessels and a
central depression
• Locally invasive
• Rarely metastasizes
• Organ transplant recipients have a 10-fold
higher risk for Basal Cell Carcinoma
compared to the general population(2)
http://www.dermatology.ucsf.edu/skincancer/professionals/types.aspx
•
•
•
•
•
Melanoma:
Neoplasm of pigment (melanin) producing cells
Brown or black skin lesion with irregularities in symmetry, border
and coloration
Prognosis dependent on depth of invasion
~100,000 new cases of melanoma are diagnosed in the United
States each year
– Only 4% of diagnosed skin cancer, but 77% of skin cancer related
deaths
•
Organ transplant recipients have a 3 to 4-fold higher risk for
melanoma compared to general population(12)
– Melanoma accounts for ~6% of post transplant skin cancers in adult
transplant recipients(13)
– Melanoma accounts for 12-15% of post transplant skin cancers in
pediatric organ transplant recipients(13)
– Transplant recipients with a pre-transplant history of melanoma
have a high risk of recurrence (~20%)(14)
Common Conditions
• Jaundice – buildup of bile produced by the liver
– Yellow color
• Cyanosis
– Bluish skin tint
– Caused by severe reduction in blood flow or
oxygenation
• Vitiligo
– Loss of melanocytes
– Loss of skin color – think Michael Jackson 
Quick Facts:
• The most readily cured type of cancer is
basal cell carcinoma
• A condition involving absence or loss of
hair is called alopecia
• Loss of skin color is called vitiligo
• A single celled layer of squamous
epithelium is found lining blood vessels
and alveoli and are called “endothelial”
cells
Diabetes
• Exposure to high blood sugar levels
damages the basement membrane
of endothelial cells (sometimes
called basal lamina). This may
cause kidney disease and blindness