Integumentary System
Skin, Hair, Nails & Glands
By the numbers…
• Accounts for 3% of total body tissue & 16%
of total body mass
Overview
• 2 major components
– Cutaneous membrane (epidermis & dermis)
– Accessory structures (hair, nails & exocrine
glands)
• Does not function in isolation
– Extensive network of blood vessels & sensory
receptors in dermis
– Deep to the dermis, the subcutaneous
(hypodermis) layer is the interwoven CT that
connects the skin to muscle & bone
Organ/ Component
Cutaneous Membrane
-Epidermis
-Dermis
Primary Function
Covers surface; Protects deeper tissues
Nourishes epidermis; Provides strength; Contains
glands
Hair Follicles
Produce hair; Innervation provides sensation
Hairs
Provides protection for head
Sebaceous glands
Secretes lipid coating that lubricates hair shaft &
epidermis
Sweat Glands
Produces perspiration for evaporative cooling
Nails
Protects & stiffens distal tips of digits
Sensory Receptors
Provides sensation of touch, temperature,
pressure & pain
Subcutaneous Layer
Stores lipids; Attaches skin to deeper structures
Functions
• PROTECTION of underlying tissues & organs
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•
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against impact, fluid loss & chemical/biological
attack
EXCRETION of salts, H2O & organic wastes
MAINTANENCE of body temp by insulation or
evaporation
SYNTHESIS of vitamin D, which is necessary
for calcium absorption
STORAGE of lipids for energy & insulation
DETECTION of touch, pressure, pain & temp
Epidermis
• Stratified squamous tissue
• Avascular
• Dominated by KERATINOCYTES (contain
protein keratin…hardener)
• Thin skin (most of body surface) 4 layers
& as thick as a plastic sandwich bag
• Thick skin (palms & soles)  5 layers & as
thick as a standard paper towel
Layers of Epidermis
• 2 names
– Stratum (pl. strata) means layers
– 2nd name refers to the function or appearance
• In order, from superficial to deep:
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Stratum corneum
Stratum lucidum
Stratum granulosum
Stratum spinosum
Stratum basale (germinitivum)
• “Come, Let’s Get Sun Burned”
Stratum Basale
• Location of mitosis (stem cells) where new cells
are produced & pushed to the surface to replace
dead ones
• Contain Merkel cells which are sensitive to touch
• Contain Melanocytes which produce brown tones
& is responsible for skin tones
• Epidermal ridges & dermal projections (papillae)
– The contours of the skin follow these ridge patterns
(loops & whorls seen on palms & soles…fingerprints)
– Unique to every individual & do not ever change
Stratum Spinosum
• Cells are far enough away from dermal blood
vessels that they begin to compact & die
• Consist of 8-10 layers of keratinized cells
attached by desmosomes (cell glue)
• Appear “spiny”
• Contains Langerhans cells, which assist in
immune response by stimulating a defense
against
– Microorganisms that manage to penetrate the
superficial layers
– Superficial cancer cells
Stratum Granulosum
• Most have stopped dividing at this layer &
begins to produce large amounts of keratin
& the cells die
• Has a “grainy” appearance
Stratum Lucidum
• Only found in thick skin (palms & soles)
• Means “clear layer”
• Thickened skin due to additional wear &
tear
• Flattened, densely packed & filled with
keratin
Stratum Corneum
• Dead cells are filled with keratin & are so
compact, they form sheets
• Cells are tough & offer protection
• Cornification means keratinized
• Replace cells worn away by wear & tear
• It takes 15-30 days for cells to move from
S. basale to S. corneum
S. Corneum (cont’d)
• Layer is water resistant, but not water
proof
– Insensible perspiration: unable to feel water
loss
– Sensible perspiration: very aware (sweating)
S. Corneum (cont’d)
• Freshwater exposure
– Water is HYPOTONIC (less dissolved minerals
than body fluids) so H2O moves into the cells,
causing them to swell (pruney fingers & toes
when in the tub or pool for a long time)
• Saltwater exposure
– Water is HYPERTONIC (more dissolved minerals
than body fluids) so H2O moves out of the cells,
causing them to shrink (prolonged exposure to
saltwater can lead to dehydration)
• Hypotonic (freshwater)
• Hypertonic (saltwater)
Concept Check
 Dandruff is caused by excessive shedding
of cells from the outer layer of skin on the
scalp. Thus dandruff is composed of cells
from which epidermal layer?
Stratum corneum
Concept Check
 Why do paper cuts hurt so bad but do not
bleed?
Because the epidermis is avascular (no blood
vessels) but innervated (sensory receptors)
Concept Check
 A splinter that penetrates to the 3rd layer
of the epidermis of the palm is lodged in
which layer?
Stratum granulosum
Concept Check
 Why does swimming in fresh water for an
extended period cause epidermal
swelling?
Freshwater is hypotonic so water moves into the
cells, causing swelling
Concept Check
 Some criminals sand or cut skin off the
tips of their fingers so as not to leave
recognizable fingerprints. Would this
practice permanently remove
fingerprints? Why or why not?
No, because cells are replaced every 15-30 days
& the patterns that cause fingerprints are
genetic & never change
Epidermal Pigmentation
(Skin Color)
• Epidermis contains 3 pigments: Carotene,
Melanin & Hemoglobin
• Carotene is an orange-yellow pigment
– Most apparent in light-skinned humans
– Accumulates in fatty tissues in deep dermis &
hypodermis
Melanin
• Brown, yellow-brown, or black pigment produced in
melanocytes
– More dominant in dark-skinned humans
– Highest concentration found in cheeks, forehead, nipples &
genitals
– Freckles are small pigmented areas
– Melanocytes are stimulated by UV light & increase melanin
production
• Melanin in kerotinocytes protects skin from harmful
effects of the sun (UV radiation)
• Some sunlight is beneficial because it stimulates the
production of a vitamin D required for calcium
absorption
Hemoglobin
• Red blood cells contain hemoglobin, which
binds & transports O2 in the bloodstream
– When bound to O2 = Bright red color
• In light-skinned people…
– Flushed or red when blood supply is increased
(embarrassed, over heated, etc)
– Pale or white when blood supply is reduced
(scared or nervous)
– Cyanotic or blue when reduced blood supply is
prolonged (extreme cold, cardiovascular or
respiratory disorders, etc)
Skin Conditions
Jaundice
– Liver is unable to excrete bile so a yellowish
pigment accumulates in body fluids
– Skin & whites of the eyes become yellow
Vitiligo
– Individuals lose their melanocytes
– 1% of population, and often found in people
with thyroid disorders or when immune
system malfunctions & attacks melanoctyes
– Cosmetic, especially for people with dark skin
Tumors of the Skin
• Benign, e.g. warts
• Cancer – associated with UV exposure (also
skin aging)
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Aktinic keratosis - premalignant
Basal cell - cells of stratum basale
Squamous cell - keratinocytes
Melanoma – melanocytes: most dangerous;
recognition:
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A - Asymmetry
B - Border irregularity
C - Colors
D - Diameter larger than 6 mm
Melanoma
Non-cancerous Skin Abnormalities
Concept Check
 Why does exposure to sunlight or
sunlamps darken skin?
Because UV rays stimulate melanocytes &
increase production of melanin, resulting in a
darker skin tone
Concept Check
 Why does the skin of a fair skinned person
appear red during exercise in hot weather?
Because oxygenated blood is increased to
the surface to allow for heat loss
Concept Check
 In some cultures, women must be covered
completely except for their eyes, when they
go outside. Explain why these women exhibit
a high incidence of problems with their
bones?
Without sun exposure on the skin, the
individual cannot produce the compound
necessary to absorb calcium, which is
needed for strong bones
Next… the DERMIS
Dermis
• Strong, flexible connective tissue:
– Your “hide”
• Cells:
– Fibroblasts, macrophages, mast cells, WBCs
• Fiber types:
– Collagen, elastic, reticular
• Rich supply of nerves and vessels
• Critical role in temperature regulation (the vessels)
• Two layers
– Papillary – Areolar CT (loose), capillaries, lymphatics,
& sensory neurons
– Reticular – “reticulum” (network) of collagen & elastic
fibers
*Dermis layers
*Dermal papillae
*
*
• Presence of Collagen & Elastic fibers permit
stretching & recoil (skin turgor = elasticity)
– Very strong
– Resist stretching
– Easily bent or twisted
• Water content helps maintain flexibility &
resilience
– Dehydration
• Extensive distortion (pregnancy or extreme
weight gain) can result in stretch marks
• With age & environmental conditions, skin loses
elasticity wrinkles result
– Retin-A (derivative of Vitamin A) can be applied as
a cream or a gel to increase blood supply &
stimulate dermis repair (reduces wrinkles)
Concept Check
Where are the capillaries & sensory
neurons that supply the epidermis
located?
Papillary layer of the dermis
Concept Check
What accounts for the ability of the dermis
to undergo repeated stretching?
Presence of elastic fibers (skin turgor)
Hypodermis
• “Hypodermis” (Greek) = below the skin
• “Subcutaneous” (Latin) = below the skin
– Also called “superficial fascia”
“fascia” (Latin) =band; in anatomy: sheet of connective
tissue
• Fatty tissue which stores fat and anchors
skin (areolar tissue & adipose cells)
• Different patterns of accumulation
(male/female)
Clinical Note
• Accumulation of excessive amounts of
adipose tissue increases the risk of
diabetes, stroke & other serious conditions
• Liposuction is a “quick fix” but it can be
dangerous. Risks include
– Anesthesia
– Bleeding (adipose is highly vascular)
– Infection
– Fluid loss
Skin appendages
• Derived from epidermis but extend into
dermis
• Include
– Hair and hair follicles
– Sebaceous (oil) glands
– Sweat (sudoriferous) glands
– Nails
Hair
• Function
– Warmth – less in man than other mammals
– Sense light touch of the skin
– Protection - scalp
• Root hair plexus
– Sensory nerves surround the base of the hair
– Feel every movement around every hair (early warning)
• Arrector pili muscles
– Contracts & pulls on follicle, causing hair to stand erect
• Fear or rage
• In our ancestors & other mammals, this makes animal appear
bigger to a potential enemy
• Insulates us when cold (traps heat close to body)…Goosebumps
Hair Structure & Production
• Hair root
– Portion that anchors the hair to the skin
• Hair shaft
– Portion that extends from the body (exposed part)
• Hair bulb
– Mass of epithelial cells that form a cap (where hair growth
begins)
• Hair papilla
– Peg of connective tissue containing capillaries & nerves
surrounded by bulb
• Hair matrix
– Layer of basal “daughter” cells are produced & pushed to
the surface
Hair and hair follicles: complex
Derived from epidermis and dermis
Everywhere but palms, soles, nipples, parts of genitalia
*
*“arrector pili” is smooth muscle
Hair bulb:
epithelial cells
surrounding
papilla
Hair papilla
is connective
tissue______________
• Core  Medulla
– Closest to center of matrix
• Intermediate layer  Cortex
– Farther from the center
• Edge  Cuticle
– Surface of hair
• As cell division continues, the hair gets
longer & keratinized (cells are dead)
• Types of hair
– Vellus: fine, short hairs (“peach fuzz”)
• Present at armpits, pubic area & limbs until puberty
– Terminal: longer, deeply pigmented, courser hair
(eyebrows & eyelashes)
• Hair growth: averages 2 mm/week
– Active: growing
– Resting phase then shed
• Hair loss
– Thinning – age related
– Male pattern baldness
• 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
Concept Check
What happens when the arrector pili
muscles contract?
Goosebumps
Concept Check
Once a burn on the forearm that destroys
the epidermis and extensive areas of the
deep dermis heals, will new hair grow in
the affected area?
Hair is a derivative of epidermis but the
follicle is in the dermis. Once destroyed,
hair will not regrow
Sebaceous glands
• Oil glands (Holocrine glands)
that discharge an oily secretion
onto hair follicles
– Secreted product is called
SEBUM
• Prohibits the growth of
bacteria, lubricates & protects
the keratin of the hair shaft &
conditions the surrounding
skin
Sudoriferous (Sweat) Glands
• Apocrine glands
– Produce a sticky, cloudy & potentially smelly
(odorous) secretion on to hair follicles
– Armpits
– Enlarge & increase secretions during puberty
• Merocrine glands (or eccrine glands)
– More widely distributed
– Most on palms & soles
– Function in cooling surface of skin to reduce body
temperature, excreting H2O & electrolytes,
providing protection from environmental hazards
Sweat glands
• Entire skin surface
except nipples and
part of external
genitalia
• Prevent overheating
• Humans most
efficient (only
mammals have)
• Produced in
response to stress
as well as heat
Other Glands
• Mammary glands
– Breasts
– Development controlled by sex hormones &
pituitary gland
• Ceruminous glands
– Modified sweat glands
– Secretions combine with those of sebaceous
glands, forming a mixture called cerumen
– Together with tiny ear hairs along the ear canal,
trap foreign particles, preventing them from
reaching the eardrum
Concept Check
What are the functions of sebaceous
secretions?
Sebum lubricates & protects the hair shaft,
lubricates & conditions the surrounding skin, &
inhibits growth of bacteria
Concept Check
Deodorants are used to mask the effects of
secretions from which type of skin gland?
Apocrine sweat glands
Concept Check
Which type of skin gland is most affected
by the hormonal changes that occur during
puberty?
Apocrine sweat glands enlarge &
increase secretions
Nails
• Made of hard keratin
• Corresponds to hooves and claws
• Grows from nail matrix
Burns
• Burns
– Threat to life
• Catastrophic loss of body fluids
• Dehydration and fatal circulatory shock
• Infection
– Types
• First degree – epidermis: redness (e.g. sunburn)
• Second degree – epidermis and upper dermis: blister
• Third degree - full thickness
First-degree
(epidermis only; redness)
Second-degree
(epidermis and dermis,
with blistering)
Third-degree
(full thickness,
destroying epidermis,
dermis, often part of
hypodermis)
Burns
How a wound heals