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Chapter 5
Integumentary System
I. Introduction
A. Organs are composed of two or
more kinds of tissues
B. Largest organ of the body is the
skin (“Integumentary System”
includes skin, hair, nails & glands)
II. Functions of the Integumentary System
A. Protection = skin protects against abrasion, UV
light, microorganisms, dehydration
B. Sensation = sensory receptors detect heat, cold,
touch, pressure, & pain
C. Vitamin D production = skin produces a
molecule that can be transformed into vitamin D
when exposed to UV light
D. Regulates body temperature = body
temperature controlled by blood flow through
skin and sweat gland activity
E. Excretion = small amounts of waste lost through
skin/gland secretions
III. Layers of the Integument
A. Hypodermis (“under + skin”) or
Subcutaneous (“below + skin”)
1.
2.
3.
4.
Attaches skin to underlying bone and muscle
Supplies skin with blood vessels & nerves
Not part of the skin
Composed of loose connective & adipose
tissue
a. Padding & insulation
b. Sex differences
c. Total body fat estimates made from
pinching hypodermis
5. Site of subcutaneous injections
B. Skin = Dermis + epidermis
•
•
Dermis = layer of dense connective tissue
Epidermis = (upon the dermis) layer of
epithelial tissue resting on dermis
a. Hypodermis = foundation of house
b. Dermis = house
c. Epidermis = roof
1. Dermis
a. Connects epidermis to underlying connective
tissue
b. Composed of collagen, elastic fibers, fibroblasts,
fat cells, & macrophages (fewer fat cells & blood
vessels than hypodermis)
i. Collagen fiber orientation can either resists or
be susceptible to stretching (cleavage/tension
lines) – Figure 5.2
c. Nerve endings, hair follicles, smooth muscle,
glands, lymphatic vessels extend into dermis
(Figure 5.1)
d. Dermal papillae = projections into upper
dermis extending toward epidermis; contain
many blood vessels (Fig. 5.3a)
i. Supply epidermis with nutrients
ii. Remove waste
iii. Regulate body temperature
iv. Found in hands & feet – fingerprints/ridges
for friction and grip
• Dermis is part of animal hide used in
making leather
• Site of injections like TB test
2. Epidermis (“upon + skin”)
a. Prevents water loss, injury, entrance of harmful
chemicals
b. Composed of stratified squamous epithelium
i. Mitosis in deepest layers, pushing older cells
to surface where they slough off
ii. Outermost cells protect those underneath
iii. Deeper replicating cells replace cells lost from
the surface
c. During migration from “deep” to “superficial”
cells change in shape and chemical composition
i. Keratinization = cells fill with keratin
• Cells die and form protective layer resisting
abrasion & forming permeability layer
d. Epidermis is stratified (strata = layer) (Fig. 5b)
i. Stratum basale = base layer
• Cuboidal or columnar cells – mitosis every 19
days
ii. Intermediate strata
iii. Stratum corneum = horny layer
• Mos superficial
• Dead, squamous cells filled with keratin
• Coated/surrounded by lipids, prevent fluid loss
• 25+ layers of dead cells joined by desmosomes
• Calluses (hard skin) = increase in number of
layers in stratum corneum due to friction
• Corn = similar reaction as callus, just over a
bony prominence
3. Skin color (Pigments in the Epidermis)
a. Determined by pigments in skin, blood
circulating in skin, thickness of stratum corneum
b. Melanin (black) = group of pigments
determining color of skin, hair, and eyes
i. Usually brown to black, sometimes yellowish
or reddish
ii. Melanocytes (black cell)
• Golgi bodies in melanocytes package
melanin into melanosomes, then
phagocytized by epithelial cells (Fig. 5.4)
•
•
•
•
•
Large amounts of melanin in freckles, moles,
genitalia, nipples, areolas
Less melanin in lips, palms, soles
Racial variations – due to amount, kind, and
distribution of melanin
All races have ~same number of melanocytes
Melanin production determined by genetic
factors, light exposure, hormones
1.
Albinism = recessive gene for deficiency/absence of
melanin
2. UV exposure stimulates melanin production = suntan
3. Pregnancy – darker nipples and areolas, genitalia,
cheekbones, forehead, chest, midline
c.
Cyanosis (dark blue color) = decrease in blood
oxygen
d. Birthmarks = congenital disorders of capillaries
in the dermis
e. Carotene = yellow pigment in carrots and
squash, lipid soluble – Vitamin A
1. Accumulates in lipids of stratum corneum & fat in
dermis and hypodermis = yellow tinted skin
IV. Accessory Skin Structures
A. Hair
1. Characteristic of all mammals
a. Thick hair = fur
2. Hair anatomy:
a. Hair shaft = portion of hair above skin surface
b. Hair root = portion of hair below skin surface
c. Hair bulb = base of hair root
d. Medulla= center of hair
e. Cortex (bark) = surrounds the medulla
f. Cuticle (skin) = single layer of overlapping cells
holding hair follicle
g. Hair follicle = extension of epidermis deep into
dermis
i. Plays role in tissue repair
3.
Hair growth:
a.
Cyclic: growth stage + resting stage
i. Hair bulb produces hair; nourished by blood vessels
ii. Epithelial cells undergo keratinization in hair bulb;
cells are added to base of hair – hair “growth”
iii. Growth stops during resting stage
iv. Next growth stage causes hair to fall out
Hair Type
Growth Stage
Resting Stage
Eyelash
30 days
105 days
Scalp
3 years
1-2 years
i.
4.
Pattern baldness – permanent loss of hair
Hair color determined by varying amounts & types
of melanin
a.
Melanin production decreases with age = gray/white
B. Muscles
1. Arrector pili (that which
raises, hair) = contraction
of these muscles cause
hair to “stand on end”…
goosebumps 
a. Composed of smooth
muscle
b. Evolutionary advantage in
mammals – traps air (heat)
for insulation, also look
larger - intimidation
C. Glands
1. Sebaceous glands
a. Simple, branched acinar/alveolar
b. Produce sebum – oily substance lubricating hair & skin
surface, preventing drying out & bacterial infection
C. Glands, continued…
2.
Sweat glands (two types):
a.
Merocrine sweat glands
i. Simple, coiled tubular w/ ducts opening
to skin surface
ii. Every part of skin, most abundant in
palms/soles
iii. Produce sweat: slightly salty water-based
secretion
• Evaporative cooling
• Emotional stress produces sweat in
palms, soles, axillae (used in lie
detector tests!)
b. Apocrine sweat glands
i. Simple, coiled tubular with ducts opening
into hair follicles of axillae & genitalia
• Become active at puberty due to sex
hormone influence
ii. Secretes thick organic substances
• Broken down by bacteria = body odor
D. Nails
1. distal ends of digits of primates
2. Nail = thin, horny plate at end of fingers and toes,
consisting of several layers of dead epithelial
cells (stratum corneum) containing a hard keratin
3. Nail anatomy:
a. Nail body = visible part of nail
b. Nail root = part of nail covered by skin
c. Eponychium or cuticle (upon + nail) =
stratum corneum extending onto nail body
d. Nail bed = nail root and nail body attach to
this
e. Nail matrix = proximal portion of nail bed
w/o nail root attached
i. Produces cells that result in nail growth
ii. Nails grow continuously
f. Lunula = whitish, crescent-shape at base of
nail
V. Physiology of the Integumentary System
A. Protection
1. Prevents water loss (lipids)
2. Prevents entry of microorganisms/foreign substances
(secretions & skin)
3. Protects against abrasion (stratified squamous epithelium)
4. Protects against UV light damage (melanin)
5. Hair: insulation (head), keeps foreign
objects/microorganisms/sweat out (eyelashes, eyebrows,
nose & ear hairs)
6. Damage protection/defense (nails)
V. Physiology of the Integumentary System, cont.
B. Sensation
1. Nervous receptors in dermis & epidermis (pain, heat, cold,
pressure)
C. Vitamin D Production
1. Vitamin D precursor made in skin, modified by liver, sent
to kidney were becomes vitamin D
2. Required for calcium & phosphate absorption in intestines
D. Temperature Regulation
1. Necessary for enzyme function
2. Blood vessels (arterioles) in dermis dilate to lose heat,
constrict to keep it in
E. Excretion
1. Removal of waste products from the body – small role
2. Sweat: water, salts, urea, uric acid, ammonia
VI. Integumentary System as a Diagnostic Aid



Cyanosis = skin appears bluish, low oxygen in blood (indicates
impaired circulatory or respiratory function)
Jaundice = skin appears yellowish, liver damage causes bile
pigment buildup
Rashes, lesions, vitamin deficiencies, iron deficiencies
A.
Burns
1.
Partial-thickness burns – part of stratum basale viable
a. First-degree burns – involves epidermis, red, painful, edema
i. Sunburn, quick exposure to hot/cold
ii. No scarring, heal quickly
b. Second-degree burns – destruction of epidermis an dermis, recovery
happens from edge of burn
c. Full-thickness or third-degree burns
i. Painless b/c nervous tissue destroyed
ii. Whit, tan, brown, black, or deep cherry red
iii. Scarring with disfiguration, extended healing time
iv. Skin grafts (self, cadavers, pigs, lab-grown?)
B.
Skin Cancer
1.
Most common type of cancer (UV
radiation, chemicals, radiation)
2. Basal cell carcinoma – stratum basale
to dermis forming an open ulcer
a. Treatment: surgery or radiation
3. Squamous cell carcinoma – cells
immediately superficial to stratum
basale
a. Produce tumors – continue
dividing, can be fatal
4. Malignant melanoma – arise from
melanocytes (moles)
a. Can be fatal (will metastasize)
VII. Effects of Aging on Integumentary System
a)
b)
Diminishing skin function due to compositional and
functional changes in its layers
Age spot = increase in number of melanocytes in some
areas vs. freckles = increase in melanin production