Biology 141
Integumentary System
Chapter 5
The Integument
Integument: Skin – largest body organ
 Integumentary System:

– Skin
– Hair
– Nails

Function:
– Protection
– Maintain body temperature
– Provide sensory input
Dermatology: medical specialty dealing with the
integumentary system
Structure of the Skin
 Cutaneous
membrane: skin
– Epidermis – superficial layer
– Dermis – deep layer
 Subcutaneous
membrane
– Hypodermis – fat layer; not technically
a part of the skin.
Structure of the Skin
 The
2 layers of
skin;
– epidermis
 Multilayered
epithelial tissue
 thinner
– Dermis
 Connective
 thicker
tissue
Epidermis

Cell types found in the epidermis:
– Keratinocytes:
multilayered
 Produce keratin protein (tough, water repellant)

– Melanocytes
 Produces
pigment melanin to protect nuclear DNA in
keratinocytes
– Langerhans cell
 Immune
response
– Merkel cells
 Contact
Merkle discs to detect sensations
Epidermis
Tissue Layers
 Composed
of different strata (layers)
– outermost - dead cells
– Innermost - Cells divide
 Cells
 Layers
die as they are pushed upward
originate from the deepest
cell layer of columnar cells called the
stratum germinativum.
Sublayers of the Stratum
germinativum

Stratum basale ("base layer")
– Cells of stratum basale are closest to the blood supply in
the dermis and are thus the healthiest
– Only these cells can reproduce

Stratum spinosum ("spiny layer")
– Cells are pushed from below and become "squished" and
look "spiny" on cross sectional view
– Because the cells are farther away from the dermal
blood supply, they are less healthy and thus don't
reproduce
Basal Cell Carcinoma




Low magnification (left) of skin cross-section of shows
different layers (epidermis, dermis and subcutaneous
tissue), and
areas of tumor invasion.
Higher magnification (right): tumor cells resemble those in
the normal basal cell layer of the epidermis.
Tumor cells appear to bud off from the epidermis and grow
downward as islands and cords of basophilic cells with
hyperchromatic nuclei.
Epidermis Tissue Layers
(deep to superficial)

Stratum germinativum ("growth layer")
– stratum basal – germination basement layer
– Stratum spinosum – “thorn-like”

Stratum granulosum "grainy layer"

Stratum lucidum "clear layer"

Stratum corneum “horny layer” (top layer)
Epidermis: Tissue Layers
 stratum
basal:
– Single row of cuboidal or columnar
keratinocytes.
– Some are stem cells
– Contains
 Melanocytes
 Langerhans
cells
 Merkle cells and discs
Epidermis: Tissue Layers
 stratum
basal –
– Damage to this layer damages stem
cells
 Unable
to regenerate skin
 Require skin grafts
 Grafts can be autologous (same individual)
or transplanted from a donor.
– Skin sheets can also be grown in the lab
Epidermis: Tissue Layers
 stratum
spinosum
– multilayered keratinocytes
– Few Langerhans cells and Melanocytes
Epidermis: Tissue Layers
 stratum
granulosum
– Multilayered, flattened keratinocytes
– Cells undergoing apoptosis
– Secretes water repellant
– cells loose nuclei, appear grainy
– Keratohyalin (a precursor to keratin)
forms in granules here
Epidermis: Tissue Layers

stratum lucidum:
– Multilayered, dead
keratinocytes

with large amount of
keratin
– Translucent and flattened
– Found only in thick skin
(hairless)



Fingertips
Palms
soles
Epidermis: Tissue Layers

stratum corneum:
–
–
–
–
–
Multilayered
Flat, dead keratinocytes
primarily keratin protein
"horny layer" - cells have processes
Flattened cells filled with keratin form
"keratinized layer" and make this "keratinized
stratified squamous epithelium"
– Constant friction results in callus formation
Dermis
 Dermis:
– Connective tissue
– Contains
 Blood
vessels
 Nerves
 Glands
 Hair follicles
Dermis
2 main regions:
 Papillary:
upper layer
 Reticular:
deep layer
Dermis
 Papillary:
upper layer
 lies
next to the epidermis
 contains the derma papillae (projections into
the upper epidermis)
– epidermal ridges creat fingerprints, palm prints
and footprints.
– Contain capillaries
– Contain Meisssner corpuscles (tactile receptors)
– Contain free nerve endings
 Senses temperature, pain, itch, tickle
Dermis
 Reticular:
deep layer
 Attaches
to the subcutaneous layer
 Dense irregular connective tissue
 contains more collagen fibers
– increasing the strength of the skin.
 Contains:
– Few adipose cells
– Hair follicles
– Nerves and Pacinian corpuscles (deep pressure)
– Sebaceous glands (oil)
– Sudoriforous glands (sweat)
Accessory Structures
 Receptors:
Meissner’s corpuscles
and Pacinian corpuscles
 Meissner’s: located in the papillary
layer of dermis
– project into the papillae.
– touch receptors
 Pacinian:
spherical, onion-like
– Lie deep in the reticular layer
– pressure
Sensory receptors in the Dermis
Meissner’s
Corpuscle detects
light touch
 Papillary layer

Pacinian Corpuscle
detects deep touch
(pressure)
 Reticular layer

Dermis
 Tears
in the reticular region of the
dermis result in stretch marks.
 Incisions
against the grain of the
collagen fibers = wide scar
 Incisions
with the grain = thin scar
Structural Basis of Skin Color

Skin color pigments:
– Melanin
– Hemoglobin
– Carotene

Melanin – number of melanocytes the
same in all people
– Amount of melanin produced varies
– Accumulation results in
 Age
spots
 Freckles
 moles
Melanin
 Function:
– Absorbs UV radiation
– Prevents damage to DNA in epidermal
cells
– Neutralizes free radicals
Hemoglobin


Found in RBCs
Skin color depends
on amount of
oxygen in the
blood
– Blue – cyanotic: low
oxygen
– Yellow - jaundice:
high bilirubin
 Liver
damage
– Red – erythema:
engorgement of
capillaries
 Injury
 Heat
 Infection
 Inflammation
 Allergic
reaction
– White – pallor: low
number of RBC
 Shock
 anemia
Carotene
 Yellow-orange
pigment found in egg
yolks and orange vegetables
– Precursor to vitamin A
– Excessive dietary intake results in
accumulation in the subcutaneous layer
Albinism / Vitiligo
 Albinism:
Inherited inability to
synthesize melanin
– Melanin is not produced in skin, hair,
and eyes.
 Vitiligo:
partial or complete loss of
melanocytes in patches of skin
– Immune system attacks and destroys
melanocytes.
Accessory Structures
Hair: pili
 Columns of dead, keratinized cells compactly cemented together.
 hair shaft – portion of the hair that
projects above the surface.
 root – portion below the surface
extending into the dermis.
Hair
 Hair
shaft and root consist of 3
concentric layers of cells:
– Medulla
– Cortex
– Cuticle
Human Hair

Cuticle showing scales


No medulla, brown
pigment granules in cortex
Light medulla
Hair

Hair follicle:
composed of the
root sheath –
encasement with 2
layers:
– Internal root sheath

produced by matrix,
surrounds root
– External root
sheath
 extension
epidermis
of
The Dermal root
sheath is part of
the dermis
Hair
 bulb
- enlarged
region of the root
containing the
follicular papilla
(involution of
loose connective
tissue).
Hair
 arrector
pili
muscle –
smooth muscle
that upon
contraction
forces the skin
into goose
bumps.
Accessory Structures
Glands: sebaceous and sweat glands
Sebaceous glands:
 Usually connected to hair follicles
 secretes sebum (oil)
 Moisturizes hair and skin

– keeps hair pliable.
– Keeps skin soft
– Inhibits bacteria
Acne:
Inflammation of a sebaceous gland.

Normal sebaceous gland

Blocked sebaceous gland
Sudoriferous Glands
(Sweat glands)
2 main types of glands: eccrine and apocrine
 eccrine:
– empty directly out through the skin surface
– tubular with a coiled basal portion located deep in the
dermis
– Regulates body temperature

apocrine:
–
–
–
–
larger, empty directly into the hair follicle canal
secretory portion located in the subcutaneous layer
Excretory duct opens into hair follicle
stimuli: psychic factors; emotions, sexual excitement
Sudoriferous Glands
 Accessory
structures and location
Ceruminous Glands
 Modified
ear.
sweat glands in the external
– Produce ear wax (cerumen)
– Provides a sticky barrier
Nails


Tightly packed, hard, keratinized epithelial
cells.
Structure:
– Nail body: visible portion
 Pink
due to capillary bed
– Free edge: part that extends past the digit
 White
due to lack of capillaries
– Nail root: portion buried in a fold of skin
Nails
Types of Skin
2
types of skin based on structure:
– Thin (hairy) skin
– Thick (hairless skin)
Functions of the Skin

Thermoregulation:

– by sweat and blood flow

– Excrete salts, water, and
small amounts of CO2 and
urea
– Absorbs lipid molecules
(vitamins A,D,E and K,
drugs, lotions, poisons,
heavy metals, steroids)
Blood reservoir
– 8-10% of blood flow

Protection
– Against external assault

Cutaneous sensations
– Tactile, pressure, pain,
temperature, tickle
Excretion and absorption

Synthesis of vitamin D
– UV light activates
precursor molecules that
can be modified by the
liver. Vit. D produces
calcitrol which aids in the
absorption of calcium in
the GI tract.
Maintaining Homeostasis: Skin
Wound Healing
 Wound
routes:
healing can occur via 2
– Epidermal Wound Healing – affects only
the epidermis.
– Deep Wound Healing – wound extends
to dermis and subcutaneous layers
Epidermal Wound Healing
 Injury
response:
– Basal cells detach from the basement
membrane.
– Hormone (epidermal growth factor)
stimulates basal stem cells to divide to
replace migrating cells.
– Migrating cells move across wound
– Cells stop migrating upon touching
other cells (contact inhibition)
Deep Wound Healing

4 phases:
– Inflammatory:
 clot
formation closes the wound, WBC kill invaders
– Migratory:
 scab
formation, epithelial cells migrate, fibroblasts
produce fibrin for scar tissue
– Proliferative:
 Extensive
growth of epithelial cells, depositing
collagen fibers
– Maturation:
 Scab
sloughs off, collagen fibers organize
Development of the Integumentary
System
 Epidermis
is derived from the
ectoderm
 Dermis is derived from the
mesoderm
Aging and the Integumentary
System
 Most
changes occur in the dermis
– Collagen fibers decrease in number
– Elastic fibers loose elasticity
– Fibroblast (produce collagen and
elastin) decrease in number
– Decrease number of melanocytes – gray
hair
– Subcutaneous adipose tissue is lost
– Healing is longer
Sun Damage

UV A rays:
– Not absorbed by the ozone layer
– Penetrate deep into skin and absorbed by
melanocytes
– Depress the immune system
– Darken the skin

UV B rays:
– Some absorbed by ozone
– Penetration of skin not as deep
– Cause sunburn
Sun Damage
 Sunscreen
– Absorb UV B, but allow UV A rays to
reach the skin
 Sunblock
– Block both UV A and UV B rays
Skin Cancer

Basal cell carcinoma
– 78% of all skin cancers
– Tumors arise from the stratum basale
– Rarely metastasize

Squamous cell carcinoma
– 20% of all skin cancers
– Arise from squamous cell of epidermis
– metastasize

Malignant melanoma
– 2% of all skin cancers
– Arise from melanocytes
– Metastasize rapidly (can kill within months)
Skin Cancer

Basal cell
carcinoma

squamous
cell
carcinoma

melanoma
Burns
 Burns
are graded by severity:
– First degree: only epidermis, red
– Second degree: all epidermis and part
of dermis, blisters
– Third degree: all epidermis, dermis and
subcutaneous layers, black
– Fourth degree: muscle layers are
burned
Burns
 Half
of all patients with over 70% of
the body burned, dies.
 Estimating
surface area for burns
uses the rule of nines.
Burns

Head and neck (front and back)
– 9%

Each upper limb (front and back)
– 9%

Trunk (front and back)
– 4 x 9% (or 36%)

Each lower limb
– 9% front
– 9% back

Perineum (anal and urogenital region)
– 1%
Pressure Ulcers
 Decubitus
ulcers caused by constant
deficiency of blood flow from
prolonged pressure against an
object.
 Occur
most often in bedridden
patients.