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Chapter 05
Lecture Outline
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5.1 Structure of the Skin
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A. Introduction
1.
2.
3.
4.
5.
6.
7.
Also called the cutaneous membrane or
the integument
Covers the entire surface of the body
Largest organ in the body; 1.8 m2
Comprised of all 4 tissue types
The integumentary system is made up of
the skin and several accessory organs
Two regions – epidermis and dermis
Hypodermis or subcutaneous tissue
attaches the skin to underlying tissue
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Skin Anatomy
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B. Epidermis
1.
General characteristics
a. Outer, thinner region
b. Made of stratified squamous epithelium
c. Five layers (strata) – deep to superficial
1) Stratum basale
2) Stratum spinosum
3) Stratum granulosum
4) Stratum lucidum
5) Stratum corneum
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2. Stratum basale
a.
b.
Just superficial to dermis
Constantly dividing; new cells are pushed to the
surface, then die and are sloughed off
c.
Cells
1) Keratinocytes – most numerous; produce
keratin, a water-proofing protein
2) Langerhans cells – macrophages
3) Melanocytes – produce melanin; skin color and
protection from UV radiation
d.
Sensory nerves
1) Free nerve endings – pain and temperature
sensations
2) Tactile cells (Merkel cells) – touch sensations
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3. Stratum spinosum
a.
b.
4.
Cells can still divide
Spiny appearance due to keratin fibers
Stratum granulosum
a. Flattened cells
b. Contain a lot of keratin and dark-staining
pigment granules
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5. Stratum lucidum
a.
b.
c.
6.
Just deep to stratum corneum
Found only in thick skin
Provides protection from constant friction
Stratum Corneum
a. Tough, uppermost layer of epidermis
b. Cells are keratinized (hardened) and
dead
c. Keratin prevents water loss and water
gain
d. Serves as a mechanical barrier against
microbes
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C. Dermis
1.
2.
3.
4.
Thicker than epidermis
Made of dense, irregular connective tissue
Dermal papillae
Collagenous fibers prevent skin from being
torn
5. Elastic fibers stretch to allow movement of
muscles and joints
6. Vascularization of dermis supplies oxygen
and nutrients to cells of dermis and
epidermis and causes temporary changes
to skin color
7. Numerous sensory nerve fibers
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D. Hypodermis
1.
2.
3.
Subcutaneous layer located below the
dermis
Composed of loose connective tissue
Adipose tissue provides energy storage,
insulation, and protective padding
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5.2 Accessory Structures of the Skin
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A. Hair
1.
2.
3.
On all body parts except the palms, soles,
lips, nipples, and portions of the external
reproductive organs
After puberty there is noticeable hair in the
axillary and pelvic regions
Hair in different parts of the body has
different growing and resting time periods
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Hair, cont
4.
Hirsutism – characterized by excessive
body and facial hair in women due to
increased production of male sex hormone
5. Alopecia – hair loss
a. Androgenic alopecia – male pattern
baldness
b. Alopecia areata – sudden onset of patchy
hair loss
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Hair, cont
6. Hair follicles
a. Formed from epidermal cells
b. Located in dermis
c. Cells become keratinized as they are
pushed out
d. Hair root – portion of hair within
follicle
e. Hair shaft – portion of hair that
continues beyond the skin
7. Sebaceous (oil) glands
8. Arrector pili muscle – smooth muscle
attached to hair follicle
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Hair follicle and hair shaft
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B. Nails
1.
2.
3.
4.
5.
Formed from specialized epithelial cells
Nail root – base of the nail
Nail body – visible portion of the nail
Cuticles – fold of skin that hides the root
Lunula (moon) – area of rapidly dividing
cells
6. Epithelial cells become keratinized as they
move away from the root
7. Pink color due to vascular dermis under the
nail body (nail itself has no color)
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Sagittal section of a nail
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C. Skin glands
1. Glands – groups of specialized cells that
produce and secrete substances into ducts
a. Sweat glands
b. Sebaceous glands
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Types of skin glands
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2. Sweat (sudoriferous) glands
a. Present in all regions of the skin; some become
more active under stress
b. Apocrine glands
1) Open into hair follicles in anal region, groin,
and armpits
2) Begin to secrete at puberty
3) Mammary glands are modified apocrine glands
c. Eccrine sweat glands
1) Open onto surface of skin
2) Active when body heats up; helps lower body
temperature
3) Sweat (perspiration) is mostly water, but also
excretes wastes
d. Ceruminous glands – modified sweat glands that
produce cerumen (earwax)
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3. Sebaceous glands
a. Most are associated with a hair follicle
b. Secrete an oily substance called sebum
1) Lubricates and waterproofs hair and skin
2) Weakens or kills bacteria on skin surface
c. If sebum collects, whiteheads or blackheads
form
d. Acne vulgaris – inflammation of the
sebaceous glands
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5.3 Disorders of the Skin
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A. General Disorders
1.
2.
3.
4.
5.
6.
Athlete’s foot – fungal infection often
involving skin of the toes and soles
Impetigo – bacterial infection common in
young children
Candidiasis – yeast infection mainly in
moist areas
Eczema – inflammation of the skin
Dandruff – caused by a dry scalp
producing flaking and itching
Urticaria (hives) – allergic reaction causing
reddish, elevated, and often itchy patches
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B. Skin cancer
1.
Introduction
a. Begins with mutation of the skin cell
DNA
b. Nonmelanoma cancers – less likely to
metastasize
1) Basal cell carcinoma
2) Squamous cell carcinoma
c. Melanoma cancers
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2. Basal cell carcinoma
a. Most common type of skin
cancer
b. Ultraviolet (UV) radiation
causes epidermal basal cells
to form a tumor
c. Signs are varied
1) Open sore that will not
heal
2) Recurring reddish patch
3) Smooth, circular growth
with a raised edge
4) Shiny bump
5) Pale mark
d. 95% of patients are easily
cured by removal
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3. Squamous cell carcinoma
1. Five times less common than
basal cell carcinoma
2. More likely to spread than
basal cell carcinoma
3. About 1% of cases result in
death
4. Triggered by excessive UV
exposure
5. Signs are the same as those
for basal cell carcinoma, but
may also resemble a wart or
scaly growth that bleeds and
scabs
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4. Melanoma
a. More likely to be malignant
b. Starts in the melanocytes
c. Has the appearance of an
unusual mole
d. Warning signs - ABCDE
1) Asymmetry
2) Borders irregular
3) Color uneven
4) Diameter greater than
6mm
5) Elevation – above the
surface; or Evolving –
changing color, size,
shape
e. Most common in fair-skinned
persons
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5. Prevention of skin cancer
a.
b.
c.
d.
e.
Use broad-spectrum sunscreens of at least
SPF15
Wear protective clothing to cover skin
Wear UV sunglasses
Stay out of the sun between 10 am and 3
pm
Avoid tanning machines
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6. Kaposi’s sarcoma
a.
Opportunistic skin cancer found in AIDS
patients
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C. Wound healing
1.
2.
Causes an inflammatory response
Steps in wound healing
a. A blood clot forms
b. White blood cells and fibroblasts move to
the injured area
c. Fibroblasts pull the margins of the
wound together and promote tissue
regeneration
d. The basal layer of the epidermis
produces new cells
e. Proliferating fibroblasts form a scar
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Process of wound healing
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D. Burns
1.
Usually caused by heat, but also
radioactive, chemical, and electrical agents
2. Burn severity affected by:
a. Extent of the burned area
1) “Rule of nines” is a technique used
to estimate the extent of a burn
2) Lund-Browder chart is used for
children
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Rule of Nines
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b. Depth of the burn
1)
First degree burn
a) Only epidermis affected
b) Redness and pain
c) No blisters or swelling occurs
2) Second degree burn
a) Extends through entire epidermis and
part of the dermis
b) Redness, pain, and blistering
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Depth of burn, cont
3)
Third degree burn
a) Destroys entire thickness of the skin
b) Surface of wound is leathery and may be
brown, tan, black, white, or red
c) Patient feels no initial pain
4) Fourth degree burn – involve tissues down
to the bone
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3. Burns are critical if:
a.
Second-degree burns cover 25% or more of the
patient’s body
b. Third-degree burns cover 10% or more of the
patient’s body
c. Any portion of the body has a fourth-degree
burn
d. Third-degree burns occur on the face, hands, or
feet
4.
Major concerns associated with severe burns:
a. Fluid loss
b. Heat loss
c. Bacterial infection
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5.4 Effects of Aging
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A. Aging effects
1.
2.
3.
4.
5.
6.
Rate of cell mitosis decreases
Dermis becomes thinner and the dermal papillae
flatten
Adipose tissue in the hypodermis decreases
Collagen decreases
Elastic fibers in upper layer of dermis are lost and
those in the lower layer become thicker, less
elastic, and disorganized
Wrinkles form because of:
a. Loose epidermis
b. Fewer fibers
c. Less padding in hypodermis
d. UV damage
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Effects of Aging, cont
7.
Limited homeostatic adjustment to heat
because of:
a. Less vasculature (fewer blood vessels)
b. Fewer sweat glands
8. Number of hair follicles decreases
9. Reduced number of sebaceous glands
10. Number of melanocytes decrease
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5.5 Homeostasis
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A. Functions of the skin
1.
Protection
a. Safeguards from physical trauma
b. Protection from UV radiation
c. Help prevent bacterial invasion
1) Sebum is acidic, which retards growth
of bacteria
2) Langerhans cells phagocytize
pathogens and alert the immune
system to the presence of pathogens
3) Outer layer is dead cells
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Functions, cont
2.
Regulation of water loss and gain
a. Keratinized cells prevent water from
entering or leaving the body
3. Assists the urinary system
a. Sensible and insensible perspiration
b. Minor role in waste removal
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Functions, cont
4.
Vitamin D production
a. Small amounts of UV radiation are
needed
b. Vitamin D leaves the skin and enters
the liver and kidneys where it is
converted to the hormone calcitriol
c. Calcitriol enhances calcium uptake
from the digestive tract
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Normal vs. Rickets
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Functions, cont
5.
Gathers sensory information
a. Sensory receptors in the epidermis and
dermis are specialized for touch,
pressure, pain, hot, and cold
b. Receptors supply the central nervous
system with information about the
external environment
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Functions, cont
6. Helps regulate body temperature
a. If body temperature rises, blood vessels
in the skin dilate and sweat glands
become active
b. If the outer temperature is cool, blood
vessels constrict
c. Arrector pili muscles contract, but
insulating effect is absent in humans
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Helps regulate body temperature, cont
d.
Hyperthermia - body temperature above normal
1) Heat exhaustion – high body temperature, low
blood pressure, profuse sweating, loss of salts
2) Heat stroke – elevated temperature, no
sweating
e.
Hypothermia – body temperature below normal
1) Uncontrollable shivering, incoherent speech,
lack of coordination
2) Leads to slow pulse, unconsciousness, shallow
breathing, and death
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