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Integumentary System
Facts about your Skin
• Inegument = means covering
• Integumentary System- skin, nails, hair,
membranes, sweat, & oil glands
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Surface Area = 1.2 to 2.2 square meters
Weight = 4 to 5 kg
Thickness 1.5 - 4.0 mm
7% of average body weight for an adult
Functions of Skin
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Protection
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Cushions and insulates and is waterproof
Protects from chemicals, heat, cold
 Not helpful against organic solvents, heavy metals or plant
oils from poison oak
Screens UV
Acid Mantel keeps down bacteria ~pH 5
Macrophages gobble up invaders
Synthesizes vitamin D with UV
Functions of the Skin
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Regulates body heat
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Prevents unnecessary water loss
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Sweat 500ml a day if about 31-32 C
vessel dilate & constrict
But Lipid soluble – Vitamins and steroids in
Sensory reception (nerve endings)
Thermoreceptors
Pacinian receptors
• Bumps and deep pressure
Meissner’s corpuscles & Merkel disks
• Aware of caress of clothing
Layers of the Skin
1) Epidermis
2) Dermis
3) Hypodermis
1) Epidermis
• Epi = Upon
• Keratinized stratified squamous epithelium
• nutrients reach by diffusion/ avascular
• Outer layer of dead skin cells called cuticle with living
level underneath
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“Ashiness” is caused by this layer of dead skin cells being
very rough and raggedy
• DUST you see around is made up of dead skin cells!
Epithelium: layers (on left) and cell types (on right)
Remember…
• Four basic types of tissue
– Epithelium – epidermis just discussed
– Connective tissue - dermis
– Muscle tissue
– Nervous tissue
2) DERMIS
Thick,
tough, leathery, flexible layer
Made of connective tissue
Vascularized – contains blood vessels
Anchors the epidermis
Critical in Temperature regulation – contract and expand
In the dermis:
• Oil glands
• Sweat glands
• Hair follicles
• Fat tissue
• Nerves
• Connective tissue
• Blood vessels
Two layers
Papillary – areolar connective tissue; includes dermal
papillae
Reticular – “rticulum” (network) of collagen and
reticular fibers
Fingerprints, palmprints, footprints
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Dermal papillae lie atop dermal ridges
Elevate the overlying epidermis into epidermal ridges
Are “sweat films” because of sweat pores
Genetically determined
Flexion creases
• Deep dermis
from continual folding
Finger Print
3) HYPODERMIS
• Subcutaneous Tissue /Hypodermis / superficial
fascia
– not really part of skin, but helps with protective
functions
– superficial to connective tissue around bones
– loose enough for free movement
– Adipose tissue – different patters of accumulation for
men and women (grows when we gain weight)
– shock absorber & insulator
– Deep pressure receptors
Cells of the Epidermis
• Keratinized stratified
squamous epithelium
• Four distinct cell
types
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Keratinocytes
Melanocytes
Merkel Cells
Langerhans’/
Epidermal Dendrite
Cells
Keratinocytes
o Most epidermal / superficial cells
o Produce keratin – “kera”= horn . Fibrous protein
that gives stretch
o Constantly in mitosis & pushed upwards
o By the time they are on the surface they are dead
o New epidermis every 25-45 days
o Friction= keratin formation is accelerated
therefore callus- a thickening of the epidermis
Melanocytes
o Spider shaped
epithelial cells that
make Melanin
o Deepest layers of the
epidermis
o Melanin made &
collects in granules
called melanosomes
o Actin filaments move
them along till they
are taken up by
Keratinocytes
o Granules accumulate
on the superficial
“sunny side” of the
Keratinocytes nuclei &
protect nucleus from
harmful UV rays
Merkel Cells
o Shaped like a spiky hemisphere
o Help with sensory of touch
Langerhans’ Cells /
Epidermal Dendrite Cells
Macrophages (pac mans) that help activate
our immune system
Layers of the Epidermis
• Thick skin= covers
palms, fingertips, and
soles of the feet
– FIVE layers/ strata
• Thin Skin= rest of the
body
– FOUR layers (no
stratum lucidum)
Deep to Superficial:
stratum basal
stratum spinosum
strata granulosum
strata lucidum
strata corneum
Epidermis and dermis of (a) thick skin and (b) thin skin
(which one makes the difference?)
Stratum basale/ stratum germinativum/
Basal Layer
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Deepest epidermal layer
Single row of cells
Attached to dermis w/ a wavy boarder line
10-25% of cells are melanocytes & their
branches
– undergoing mitosis
stratum spinosum/
Prickly Layer
• several cell layers thick
• keratinocyte in this layer are spiny
strata granulosum/
Granular Layer
• 3-5 cell layer
• keratinocyets flatten & start to die
– not enough oxygen and nutrients b/c pushed
away from blood source
strata lucidum/
Clear Layer
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o
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thin translucent band
only in thick skin
start making distinct layer
strata corneum/
Horny Layer
• 20-30 cells thick
• ¾ of epidermal thickness
• thickened plasma membrane of cells protects
from abrasion & penetration
• glycolipid acts as a “water proof”
• protects body from heat and water loss
• “dandruff” 18kg= 40 lbs in a lifetime
Skin Color
1. Melanin
• same # of melanocytes
• kind + amount of melanin made & retained
– Darker = more darker melanosomes & retain longer
• Freckles & pigment moles are accumulation of
melanin
• Sunlight causes melanin buildup
– to protect from UV
Skin Color
2. Carotene
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Yellow-orange pigment
Accumulate in the stratum corneum
Palms of hands, soles of feet
Eat lots of rich carotene foods- becomes more obvious
3. Hemoglobin
– Pinkish hue of light skin b/c can be seen through light
skin
Skin Appendages
• Derived from
epidermis but extend
into dermis
• Include
– Hair and hair follicles
– Sebaceous (oil) glands
– Sweat (sudoiferous)
glands
– Nails
HAIR
• Hair growth: averages 2 mm/week
– Active & Resting phase then Shed
– At the base of the follicle, hair papilla
• Contains blood vessels and nerves
Bulb
• Contains matrix – epithelial cells responsible for
growth
– Contains melanocytes
• Functions of hair
– Warmth
– Sense light touch of the skin
– Protection – scalp
• Hair color
– Amount of melanin for black or brown; distinct
form of melanin for red
– White: decreased melanin and air bubbles in the
medulla
– Genetically determined though influenced by
hormones and environment
Hair and hair follicles: complex
Derived from epidermis and dermis
Everywhere but palms, soles, nipples, parts of genitalia
*
Hair papilla
is connective
tissue________________
*“arrector pili” is smooth muscle
Hair bulb: epithelial
cells surrounding
papilla
Nails
• hard keratin
• Corresponds to hooves and claws
• Grows from nail matrix
Sebaceous (oil) glands
• Entire body except palms and soles
• Oils and lubricates
Sweat Glands
• Entire skin surface
– except nipples and
part of external
genitalia
• Prevent overheating
• 500 ml to 12 L /day!
• Humans most
efficient (only
mammals have)
• Produced in response
to stress as well as
heat