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Anatomy and
Physiology I
BIOL 2401
Chapter 5
Integumentary System
Integumentary system:
• Skin
• Accessory
structures
– glands, hair,
nails, sensory
receptors
Functions of the Skin
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Protection
– Stratified epidermis…protects from abrasions
– Sweat and sebum…protects from bacterial infections
– Keratin…water proofing
– Melanin…protects from UV
– WBC in dermis…immunity
Temperature regulation
– Sweat…evaporates to cause cooling
– Blood vessels…vasoconstriction/vasodilation to regulate heat loss from warm
blood in the skin
– Arrector pili…goose bumps
Sensation
– Nerves to sense touch, temperature and injury (pain)
Excretion
– Sweat…salts, lactic acid, urea
Synthesis of vitamin D
– For absorption of calcium
Skin
Two parts/layers:
• Epidermis
• Dermis
*Subcutaneous layer attaches the skin to underlying muscles
Skin - Epidermis
Stratified squamous epithelium
Composed of 4-5 layers:
• Stratum corneum
• Stratum lucidum
• Stratum granulosum
• Stratum spinosum
• Stratum basale
Four Principle Cells of the Epidermis
• keratinocytes produce the protein
keratin, which helps protect the skin
and underlying tissue from heat,
microbes, and chemicals, and
releases a waterproof sealant
• Melanocytes produce the pigment
melanin which contributes to skin color
and absorbs damaging ultraviolet (UV)
light
• Langerhans cells- derived from bone
marrow
– participate in immune response
• Merkel cells contact a sensory
structure called a tactile
(Merkel) disc and function in the
sensation of touch
Skin Epidermis
Stratum corneum:
• Top layer with flat, dead cells
• Packed with keratin
• Continuously shed as dander
Stratum lucidum:
• Dead keratinocytes
• Present only in thick skin (palm, sole)
Stratum granulosum:
• Keratinocytes making keratin
• Degenerating nucleus…dying cells
Stratum spinosum:
• Live, non-dividing keratinocytes
• Phagocytize melanin from melanocytes
present in S basale
Stratum basale:
• Deepest layer
• Actively dividing cuboidal cells
• Produce new cells that are pushed
upwards to become keratinocytes of S
spinosum
• Have melanocytes (make melanin) and
Merkel cells (touch sensation)
Skin - Dermis
Connective tissue layer
• collagen & elastic fibers
• fibroblasts, macrophages
& fat cells
Contains
• hair follicles
• glands
• nerves
• blood vessels
Two major regions
• papillary region
• reticular region
Skin - Dermis
Papillary region:
• Areolar (loose) connective
tissue
• Upper region of dermis
• Has finger like projections dermal papillae
• Contains capillaries that
feed epidermis
• Contains Meissner’s
corpuscles (touch) & free
nerve endings for
sensations of heat, cold,
pain, tickle, and itch
• Dermal papillae reflect on
the surface as epidermal
ridges and fingerprints –
increase friction for grasping
objects
Skin - Dermis
Reticular region:
• Dense connective tissue
• Lower region of dermis
• Has glands, hair follicles
and fat tissue
• Specific arrangement of
collagen fibers reflect on the
surface as cleavage lines
and wrinkle lines
• Provides strength and
ealsticity to the skin
Skin - Hypodermis
Also referred to as:
Subcutaneous layer
Superficial fascia
Made of adipose tissue (loose
connective tissue)
Attaches skin to the underlying
muscle layers
Skin Color
Three main factors affecting skin color:
1. Melanin:
Brown pigment
Gives brown color to the skin
Made by melanocytes in S basale layer
Pigment phagocytized by keratinocytes of
upper layers of epidermis
Amount of pigment is controlled by:
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Genetics
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UV exposure
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Hormone
2. Carotene:
–
Yellow pigment (also found in yellow
fruits and vegetables)
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Used to make vitamin A
–
Gives yellow hue to the skin
3. (Hemoglobin) Blood capillaries:
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Network of capillaries varies in dermis
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Gives reddish color to the skin
Skin color clues:
• Jaundice - yellowish color to skin and whites of eyes
due to the buildup of yellow bilirubin in blood from
liver/blood disease
• Cyanosis - bluish color in the nails and skin due to
oxygen circulation deficiencies
• Erythema: redness of skin due to dilation of blood
capillaries in the dermis, caused by inflammation,
infection, allergy or burns
Albinism: melanocytes are present but melanin gene is
mutated  little or no melanin made  no color in the
skin, hair and eyes
Vitiligo: partial or complete loss of melanocytes  patchy
skin
Accessory Structures of the Skin
Formed by the epidermis
Hair - Hair follicle
• Glands
– Sudoriferous gland
– Sebaceous gland
• Nails
Accessory Structures of the Skin - Hair
Hair parts:
• Shaft
• Root
Made of:
• medulla, cortex & cuticle
Hair follicle:
• Jacket that surrounds hair root
• Made by pushing in of the S basale and S spinosum of the epidermis
• Base of the follicle
– Bulb
• Surrounded by touch sensitive nerves – hair root plexus
• blood vessels
• germinal cells in papilla for hair growth
Arrector pili:
• Smooth muscle band - attaches follicle to epidermis
• Contracts  goose bumps
Accessory Structures of the Skin - Hair
Hair Color, Growth and Function
Hair color depends upon amount and type of melanin:
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Dark hair – a lot of melanin
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Red and blonde hair – different type of melanin
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Gray hair – decrease in melanin production (decreasing tyrosinase)
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White hair – absence of melanin and presence of air bubbles in hair medulla
Hair growth cycle:
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Growth stage
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lasts for 2 to 6 years
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matrix cells at papilla of hair root producing cells
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Resting stage
– lasts for 3 months
– cells accumulate keratin & follicle atrophies
Old hair falls out and growth stage begins again
Normal hair loss is 70 to 100 hairs per day
Growth and replacement cycle affected by illness, diet, high fever, surgery, blood loss,
severe emotional stress, and gender (hormones).
Chemotherapeutic agents affect the rapidly dividing matrix hair cells resulting in hair
loss.
Function: protects from sun, prevents heat loss, and provides touch sensitivity
Glands of the Skin
Exocrine glands:
• Sebaceous (oil) glands
• Sudiferous (sweat) glands
• Ceruminous (wax) glands
• Mammary (milk) glands
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Glands of the Skin
- Sebaceous Gland
Usually connected to hair follicles
Absent in the palms and soles
Located in the dermis
Exocrine gland
– produce sebum
• contains cholesterol, proteins, fats & salts
– secretions are stimulated by hormones at puberty
• Function:
• moistens hairs
• waterproofs and softens the skin
• inhibits growth of bacteria & fungi (ringworm)
Acne
– bacterial inflammation of glands
Glands of the Skin - Sudoriferous Gland
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Located in the dermis
Duct opens on to the surface of the skin
Function:
– regulates body temperature through evaporation (perspiration)
– help eliminate wastes such as urea
Sweat: water, salts, urea, lactic acid, ammonia….
Eccrine sweat glands
Apocrine sweat glands
1. Located all over the body, more
in the palm and soles
limited in distribution to the skin of
the axilla, pubis, and areolae
2. Secretory portion is in dermis
with duct to surface
secretory portion in dermis
duct that opens onto hair follicle
3. Active right after birth
Active after puberty
4. Secretion is commonly referred
to as “sweat”
secretions are more viscous, and
have a distinct odor.
5. regulate body temperature
through evaporation
(perspiration)
help eliminate wastes such as
urea.
Glands of the Skin – Other Glands
Ceruminous (wax) glands:
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Present in the skin lining the external canal of the ear
Modified sudoriferous gland
Secretes a waxy liquid (cerumen)
Function: Protection against moisture and insect entry into the ear
canal
Mammary (milk) glands:
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Located between the pectoralis major muscle and the skin
Modified sudoriferous gland
Secretes milk
Function: Nutrition for the newborn
Nails
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Made of thick, keratinized epidermis
Divided into:
• Nail body - visible part
• Nail root – embedded into the skin
Lunula: white region of the nail
body…thickened stratum basale
Eponychium (cuticle): stratum
corneum layer that projects over the
nail body
Nail growth: in the nail matrix
surrounding the nail root
Thick vs. Thin Skin
Mostly refers to differences in epidermis of the skin
Thin Skin
• Skin is thin and smooth
• Most regions of the body
• Epidermis has four layers:
– S corneum
– S granulosum
– S spinosum
– S basale
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S corneum is thinner
Sebaceous glands are present
Fewer sudoriferous glands
Fewer sensory receptors
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Thick Skin
Skin is thicker and rougher
Specific regions – palm and sole
Epidermis has five layers:
– S corneum
– S lucidum
– S granulosum
– S spinosum
– S basale
S corneum is thicker
Seceous glands are absent
More sudoriferous glands
More sensory receptors
Skin Wound Healing
Two types of injuries:
• Superficial wounds
– Such as abrasions and superficial burns
– Healing may take 24 – 72 hours
• Deep wounds
– Such as deep lacerations or surgical
incisions
– May take days to months
Skin Wound Healing – Superficial Wound Healing
Stratum basale cells from the periphery of the wound
 migrate towards the center
 divide to make new epidermal cells
 replace the lost tissue
 cells become keratinized and pick up melanin
 skin becomes normal
Skin Wound Healing – Deep Wound Healing
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Inflammatory phase – Bleeding is
stopped by a clot; WBC migrate to
clean up
Migratory phase – Clot dries to
form scab; S basale cells of
epidermis migrate under the scab;
Fibroblasts of the dermis migrate
to form new fibers
Proliferative phase – Extensive
activity of epidermal cells to make
new epidermis; Continued addition
of fibers to form new dermis; New
blood vessels grow in
Maturation phase – The scab
comes off; New skin appears from
underneath; Scar tissue is lighter
and may lack accessory structures
Skin Burns:
Clinical Applications
Caused by: Fire, electricity, radiations, and chemicals
Effects on the body: Dehydration, lowered body temperature,
decreased blood pressure, decreased or no urine production
(kidneys shut down), infections
• First degree burn – epidermis is damaged  erythema, pain, flaking
and peeling
• Second degree burn – epidermis and part of the dermis is damaged
 erythema, blister formation, pain, partial loss of skin functions
and some scarring
• Third degree burn – epidermis, dermis and accessories lost 
marble white area surrounded by redness, major scarring
Skin Graft:
• Autograft – skin from one area to another area of the same
individual
• Isograft – skin from an identical twin…matching MHC antigens
• Homograft – temporary graft skin from another person (donor,
cadaver, foreskin)
• Heterograft – temporary grafts from another animal
• Synthetic skin – artificial skin, temporary use only.
Skin Cancer
• 1 million cases diagnosed per year
• 3 common forms of skin cancer
– basal cell carcinoma (rarely metastasize) more than 70%
cases
– squamous cell carcinoma (may metastasize) approx 25%
cases
– malignant melanomas (metastasize rapidly) approx 5%
cases
• most common cancer in young women
• arise from melanocytes ----life threatening
• key to treatment is early detection watch for changes in
symmetry, border, color and size
• risks factors include-- skin color, sun exposure, family
history, age and immunological status
Clinical Applications
Psoriasis: more rapid division of the stratum basale  thicker S
corneum  dry scales and flakes on the surface
Callus and Corns: frequent friction on skin over a bone 
thicker S corneum  painful thickening
Stretch marks: due to sudden stretching of the reticular region
of the dermis
Tattoos: special pigments used to permanently color the dermis
Aging and Integumentary System
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Number of fibroblasts and fibers decrease
– Skin looses it’s elasticity and attachment to underlying layers
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WBC (macrophages) does not protect
– Infections
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Loss of subcutaneous fat
– Skin becomes thinner
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Decrease in activity of sebaceous and sudoriferous glands
– Skin dries, cracks and gets infected
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Decrease in melanocyte number and activity
– Skin color becomes patchy