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Chapter 5
Integumentary System
Your Skin Is Your Friend!
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Hypodermis
Loose connective tissue beneath skin – also referred to as
subcutaneous tissue or superficial fascia - it is superficial to the
muscle which is deep (remember: superficial/deep are directional
terms)
Much of the body’s fat (50%) may be stored in the hypodermis
Measuring fat in this tissue at specific sites can provide an
estimate of total body fat.
Subcutaneous injections are designed to reach this area.
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Yes, that’s why those sharp things are called ‘hypodermic’ needles
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Layers of the Skin
Dermis – inner layer - largely dense irregular connective tissue,
the dermis is the ‘leather’ of the skin
Epidermis – outer layer primarily stratified squamous epithelium
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Dermis
Two layers of dermis include:
¾Reticular Layer (deep)
¾Papillary Layer (shallow)
Reticular layer – (deeper layer) of dense irregular connective
tissue. This layer sits on the hypodermis. Fibers within this layer
are arranged to form cleavage lines.
Cuts along cleavage lines are more likely to heal without scar
formation.
Overstretched skin may rupture these cleavage lines forming
stretch marks
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Dermal Layers continued
Papillary Layer – finger-like projections or bumps protrude
toward the surface of the skin. Fibers less dense than in the
reticular layer. Many blood vessels located here
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Epidermis
Stratified Squamous Epithelium… like all other epithelia these
cells are supported on a basement membrane. This membrane
separates epidermis from dermis.
No blood vessels enter the epidermis. All nourishment comes
from diffusion from capillaries in the dermis.
Keratinocytes – most of the epidermal cells produce a protein
complex called keratin. These cells provide strength & a
physical barrier to prevent bodily fluids from leaking out as well
as keeping infectious agents out of the body.
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Additional Cells of the Epidermis
Melanocytes – pigment producing cells found in deep layers of
epidermis make the skin pigment Melanin
Langerhans’ Cells – immune system cells help fight local
infections
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Langerhans’ Cells – immune system cells
Cell Production in the Epidermis
Cells in the lower layers divide by mitosis
Newly made cells push up older cells closer to the surface. As
cells rise to higher layers they change chemically & change
shape. Cells flatten out and die as the cytoplasm is replaced with
the protein complex called keratin (keratinization)
This outer layer of keratinized cells resist abrasion and fluid loss
Outer layers of cells are sloughed off in a process called
desquamation (cell life averages 40-55 days)
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Layers of the Epidermis
(from bottom to top)
Stratum Basale – single layer of cuboidal cells attached to
basement membrane & each other by desmosomes – these divide
by mitosis to make two new cells.
¾One cell stays in this layer
¾Other becomes a keratinocyte and is pushed toward the surface.
Stratum Spinosum – 8-10 layers of multi-sided cells.
Occasionally some cell division takes place in these cells
Since these two layers are the source of all new cells they are
sometimes together referred to as the Stratum Germinativum
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Layers of Epidermis continuing upward
Stratum Granulosum – 2-5 cells thick these are beginning to
flatten into diamond shaped cells. The cells contain protein
granules of keratohyalin (hence the name ‘granulosum’). Cells in
this layer begin to die and in upper layers are dead.
Stratum lucidum – thin layer present in some body areas, not in
others. Contain keratin but not keratohyalin. Appears clear
compared to surrounding layers hence the name lucidum “clear”
Stratum corneum – a few to 25 cells thick. These are thin, flat
dead cells containing keratin & surrounded by lipid. These
‘cornified’ cells flake away when the desmosomes holding them
together break down
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Thick vs. Thin Skin
Epidermis varies in thickness in different regions of the body
Thick Skin has all five layers as previously described and can be
found in areas which experience high friction or pressure.
Dermal Papillae of thick skin arranged in ridge-like patterns that
produce ‘fingerprints’
¾Soles of feet
¾Palms of hands
¾Fingertips
Thin Skin – most of the rest of body surfaces. Stratum lucidum
often absent in these areas. Fewer cells in each layer than
previously described (thickness varies). Hair is found only in
thin skin (no hair in thick skin)
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Thick Skin – note lack of hair follicles, presence of stratum lucidum and general thickening
of layers as compared to thin skin
Damage to Skin - Burning
1st-degree burns: epidermis only – painful, may cause redness &
swelling. Heal within days, no scar.
2nd-degree burns: damage to epidermis and dermis (not fully
penetrating dermis). Painful!
¾minor dermal damage – heal in 1-2 weeks, no scar
¾deeper dermal damage – heal in several months, may scar
3rd degree burns: full thickness of dermis destroyed. Usually
little pain since pain receptors are destroyed. long healing time
required, scars occur, may require skin grafts to heal.
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“First Degree” Burn - No penetration into dermis
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Superficial “Second Degree” Burn
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Deep “Second Degree” Burn
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“Third Degree” or Full Thickness Burn
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Skin Color
Melanin – a group of chemical pigments produced by specialized skin
cells called melanocytes. Melanocytes are usually found just above the
Stratum Basale. Melanin probably protects against UV radiation.
Humans of all races have approximately the same number of
melanocytes. Skin color is determined by amount & type of melanin
produced.
Melanin pigments produced range from brown & black through yellow
& red. All originate with the amino acid tyrosine. Melanin packaged
in vesicles called melanosomes.
Melanosomes are taken in by cells surrounding the melanocytes
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So, just what effect can
sunlight have on aging skin?
Albinism & Other Color Changes
A mutation which affects the ability of melanocytes to produce
tyrosinase, the enzyme required to convert tyrosine into pigment
molecules.
Thus albinos of all races are caused by the same mutation
Hormone fluctuations (especially in pregnant women) can cause
increased production of melanin.
Excess carotene (a plant pigment) in the diet can cause temporary
yellowing of the skin.
MOVIE BREAK
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Skin Accessory Structures
¾Hair
¾Muscles
¾Sweat glands
¾Oil glands
¾Nails
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Body Hair
Found in all body skin except palms, soles, lips, nipples, distal
phalanges and some parts of external genitalia
Fetus at 5-6 months develops a ‘pelt’ of hair called lanugo. This
is lost perinatally (near time of birth).
Vellus = short, fine hairs replace lanugo and remain the
predominant body hair until puberty.
Terminal hairs replace vellus at puberty, especially in pubic
region & axilla (armpits), chest & face of males (& some
females)
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Hair Structure
Shaft of hair protrudes above the skin
Root of hair is below the skin. The base of each hair expands into
the hair bulb
The hair consists of three layers (inner to outer)
medulla, cortex & cuticle
The hair follicle which supports & nourishes the hair also has
three layers (inner to outer)
internal epithelial sheath, external epithelial sheath, dermal root
sheath
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Hair Structure
Melanocytes in the root impart color to the hair
The outer cuticle of hair contains hard keratin which contains
relatively large amounts of sulfur
Sulfur accounts for the unpleasant smell of burnt hair.
Sulfur to sulfur bonds (disulfide bonds) attach proteins in the hair
shaft to each other. These bonds are temporarily broken then
reformed during a ‘permanent’ hair treatment.
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A microscopic view shows cuticle scales that resemble scales on
a fish
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Muscles
Arrector Pili – muscle associated with individual hair follicles
A.P. muscles contract when you are cold or frightened forming
‘goose bumps’ causing hairs to become erect
evolutionary holdover – benefits to furry animals in cold or fright
situations but no significant benefit to humans
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Sebaceous Glands
Oil producing glands mostly associated with hair follicles.
These glands produce sebum – an oily lipid based secretion to
lubricate the hair
¾shape – alveolar (‘grape clusters’)
¾branching – may be simple or compound
¾production method – holocrine
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Merocrine Sweat Glands
“Cooling Sweat” & “Nervous Sweat”
Two regions
¾deep coiled section (in dermis) produces isotonic fluid: water with salt
(NaCl), ammonia, urea, uric acid & lactic acid
¾duct – passes through epidermis - recovers much of the NaCl
Produce hyposmotic solution which we call sweat
reminder: hyposmotic = less salty than body fluids
Shape – coiled simple tube
Branching – simple, unbranched
Production Method - merocrine
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Apocrine Sweat Glands
“Stinky Sweat”
These glands are located at axillae, genitalia, & anus
Opening often into hair follicle above sebaceous gland
Bacterial breakdown of organic compounds in apocrine sweat is
responsible for body odor
Shape – coiled tube
Branching - compound
Production Method – merocrine (once thought to be apocrine,
name still retained)
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Other Skin Glands
Cerumen or Ear Wax Glands – located in external auditory
meatus (ear canal) genetic variability seen: two versions
¾gray, flaky (recessive)
¾yellow, sticky (dominant)
Mammary Glands – milk producing glands that are
anatomically similar to apocrine sweat glands (discussed in more
detail during reproductive chapter)
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Nails
Used by humans for grasping & scratching
Several layers of keratinized epithelium
Features/Structures include:
Nail Root – proximal & under skin
Nail Body (distal) - primary, visible portion of nail
Lunula – region of nail matrix near base, obscures blood vessels
in nail bed beneath so it appears white
Nail Bed – the area beneath the nail (produces a portion of nail)
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Nails continued
Nail Matrix – the proximal region of the nail bed - majority of
nail made here
Nail Groove – indentation in skin on edges of nail
Nail Fold – skin on lateral edges of nail. Edges of n.f. grows
onto nail as…
Eponychium (cuticle) – stratum corneum growing onto edge of
nail (except at free edge at distal end)
Hyponychium – thickened stratum corneum under distal end of
nail
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Functions of Integument
Provide a physical barrier preventing entry of foreign materials
& loss of body fluids. Protects from abrasion.
Vitamin D Production – begins in skin as UV radiation converts
7-dehydrocholesterol into vitamin D precursor cholecalciferol
which travels into blood where it travels to the liver and is
activated as vitamin D.
Temperature Regulation –when overheated blood vessels in
skin dilate to permit more blood flow into skin. Sweating allows
skin to be cooled by evaporation which cools this increased blood
volume.
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Functions of Integument continued
Excretion – removal of wastes in sweat : urea, uric acid,
ammonia
Sensory Input from environment – many nerve receptors detect
various modalities (types of sensation)
¾pain
¾heat
¾cold
¾pressure (light, deep, vibration)
¾hair movement (nerves innervating follicles)
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Aging Skin
Diminished blood flow results in thinner skin.
Elastin fibers decrease
loss of hypodermis results in sagging & wrinkles
melanocytes decrease through much of skin but remain or
increase in some areas such as hands & face resulting in age
spots
Decreased melanin produciton also results in gray/white hair
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Read Clinical Focus (pp 158-161)
possible source for bonus questions…
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