Integumentary System
Honors Biology
Power point for copying
Essential question
• What are the ways skin protects the
body?
Integumentary system
• functions:
1. protecting the body
2. helping to regulate body temperature
3. allows you to sense stimuli in your
environment
4. stores blood
5. synthesis of vit. D
6. excretion & absorption of materials
Structure of the skin
• skin = cutaneous membrane
• largest organ of body
– in adults: covers ~ 2 m² & weighs ~ 4.5 – 5 kg (10
– 11 lb)
• 2 parts:
1. epidermis
2. dermis
3. sub Q below dermis & not technically part of
skin: contains fat (insulation), & blood
vessels, nerves that supply the skin
Epidermis
• keratinzed stratified squamous
epithelium
• 4 main cell types:
1. keratinocytes
2. melanocytes
3. Langerhans cells
4. Merkel cells
keratinocytes
• ~ 90% of all epidermal cells
• produce fibrous protein: keratin:
– protects skin & underlying tissue from
• heat
• microbes
• chemicals
• also release a water-repellant sealant
from lamellar granules
– decreases water entry/loss
– inhibits entry of foreign materials
melanocytes
• ~8% of epidermal cells
• produce melanin  keratinocytes
– pigment (yellow-red to brown-black) that
contributes to skin color
– * absorbs UV radiation
– “covers” nucleus in keratinocyte
Merkel Cells
• least numerous of epidermal cells (>1%)
• deep in epidermis
• in contact with Merkel disc (tactile
disc)
• together detect different aspects of
touch
Thin Skin
• covers most of body
• 4 layers:
1. stratum basale
2. stratum spinosum
3. stratum granulosum
4. stratum corneum
Thick Skin
• found in areas where exposure to
friction is the greatest
• “thick” because has 1 extra layer:
– stratum lucidum (between stratgum
granulosa & a thicker stratum corneum)
psoriasis
• common & chronic skin disorder in which
keratinocytes divide & move more quickly
than normal from stratum basale 
stratum corneum
– make abnl keratin  flaky, silvery scales @
skin surface
– most often over knees, elbows, or scalp
Dermis
• 2nd, deeper layer of skin
• composed mostly of CT
• 2 regions:
1. papillary region
2. reticular region
Papillary region of dermis
• ~ 1/5th of total dermis
• surface area greatly increased by
finger-like structures: dermal papillae
that project into epidermis
– contain:
• capillary loops
• tactile receptors: Meissner corpuscles
• free nerve endings (temp, pain, tickle, itch)
Epidermal ridges
• develop during 3rd month of fetal
development
• pattern is genetically determined &
unique to individuals (x identical twins)
• on finger tips ridges deeper  finger
prints
– allow you to grasp things by increasing
surface area
Reticular region of dermis
• attached to subcutaneous layer beneath
• contains:
– dense irregular CT
– hair follicles
– sebaceous glands
– sudoriferous (sweat) glands
– collagen & elastic fibers (gives skin its
elasticity, strength): extreme stretching 
striae (stretch marks)
Basis of skin color
• 3 pigments contribute:
1. Melanin
2. Hemoglobin (hgb)
3. Carotene
melanin
• made from a.a. tyrosine using enzyme
tyrosinase then stored in organelle
called a melanosome
• exposure to UV light increases
enzymatic activity & more (& darker)
melanin produced
• melanin absorbs UV radiation preventing
it from damaging DNA which  skin
cancer
hemoglobin
• in RBCs  rosy color to lighter skinned
individuals
• blushing: due to increased blood flow
(autonomic nervous system at work)
Carotene
• yellow-orange pigment
• precursor of vit. A
albinism
• inherited inability to produce melanin
• most due to cell’s inability to produce
tyrosinase
vitiligo
• partial or complete lack of melanocytes
from patches of skin produces irregular
white spots
• ? Immune system malfunction?
Skin color as diagnostic clue
• cyanotic: when blood not adequately
oxygenated mucous membranes, nail beds
& skin appears bluish
Skin color as diagnostic clue
• jaundice: due to build up of bilirubin
(yellow pigment) in skin, sclera; usually
indicates liver disease
Skin color as diagnostic clue
• erythema: redness of skin caused by
engorgement of capillaries due to:
injury, infection, inflammation, allergic
reaction
Skin color as diagnostic clue
• pallor: paleness of the skin, seen in
shock & anemia
Accessory structures of the
skin
• all develop from embryonic epidermis
• include:
– Hair
– Nails
– Glands
Hair (pili)
• present on most skin surfaces x palmar
surfaces of hands, soles & plantar
surfaces of feet
• genetic & hormonal influences
determine the thickness & pattern of
distribution of hair
hair
• functions:
• protection
– scalp, eyebrows, eyelashes: from getting
foreign objects in eyes
– nose, ear canals: trap foreign objects
• sensitive to light touch
– touch receptors in hair root plexus
Hair
• composed of columns of dead,
keratinized cells bonded together by
extracellular proteins
Anatomy of a hair
• shaft: portion of hair that projects
from scalp
• root: portion below scalp
• follicle: surrounds root of hair
• arector pili: smooth muscle extends
from side of hair follicle  superficial
dermis
Types of hair
• lanuga: grows on fetus @ ~ 5 months
fetal age; sheds b/4 birth
• vellus hair: short, fine hair that grows
over baby @~ 2-3 months after birth
• terminal hair: coarse hair that develops
after puberty
Hair color
• mostly due to amt & type of melanin in
keratinzed cells
• dark hair has eumelanin
• blondes & redheads have pheomelanin
• gray: loss of melanin
• white: loss of melanin + air bubbles in
shaft of hair
Skin glands
• exocrine glands ass’c with the skin:
1. sebaceous glands
2. sudoriferous glands
– eccrine sweat glands
– apocrine sweat glands
Sebaceous glands
• “oil” glands
• most connected to hair follicles
– rest secrete directly onto surface of skin
(lips, eyelids, genitals)
• secrete oily substance called sebum
onto hair
• keeps hair from getting brittle
acne
• inflammation of sebaceous glands
colonized with bacteria
• infection  cyst which destroys
epidermal cells (cystic acne)
• acne is not caused by eating chocolate
or fried foods
Sudoriferous glands
• sweat glands
•  sweat onto skin surface or hair
follicles
Ceruminous glands
• modified sweat glands in external ear
canal skin (subQ layer)
• secrete cerumen (ear wax
– provides a sticky barrier that impedes
entrance of foreign bodies
nails
• plates of tightly packed, hard, dead,
keratinized epidermal cells that form a
clear, solid covering over the dorsal
surfaces of the distal portions of the
20 digits
• average growth ~ 0.04 in/wk
– fingernails grow slightly faster than toe
nails
Functions of a nail
• help us grasp & manipulate small objects
• protect ends of digits
• allows scratching
Parts of exterior of a nail
Parts of a nail
• body: visible part
• root: part buried
• matrix: where cells divide to produce
growth
Functions of the skin (#7)
1. Thermoregulation
– the homeostatic regulation of body
temperature
– skin achieves this in 2 ways:
1. sweating
•
evaporation of sweat requires nrg (body heat) so
body cools down as sweat evaporates
2. adjusting flow of blood in dermis
•
•
vessels dilate when body too warm
vessels constrict when body too cold
Functions of the skin
2. Blood Reservoir
• skin carries ~ 8 – 10% of total blood
flow in resting adult
Functions of the skin
3. Protection
• keratin protects underlying tissues
•
lipids released retard evaporation of water from skin
surface
• sebum moistens skin & has antibacterial properties
• acidic pH of sweat bacteriostatic
• melanin protects DNA in skin cells from UV damage
• Langerhans cells alert immune system if microbes does
attack / macrophages ingest microbes
Functions of the skin
4. Cutaneous Sensations
• skin contains variety of nerve endings &
receptors
– touch
– pressure
– vibration
– tickle
– pain
– temperature
Functions of the skin
5. Excretion
• elimination of wastes from the body
• only small amt substances excreted from
skin
– ~400 mL water/day
– ~200 mL sweat (sedentary adult)
– small amts salts, CO2, NH3, & urea
Functions of the skin
6. Absorption
• passage of materials from external environment
 body cells
• absorption of water-soluble materials negligible
• lipid-soluble materials do absorb:
–
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fat-soluble vitamins (A, D, E, K)
certain drugs (can be administered transdermally)
gases: O2 & CO2
toxins: acetone, CCl4, salts of Hg, Pb, Ar, substances
in poison ivy & poison oak
Functions of the skin
7. Synthesis of Vitamin D
• requires activation of a precursor molecule in
the skin by UV rays in sunlight  modified by
enzymes in liver & kidneys  producing
calcitriol the most active form of vit. D
• calcitriol: aids in absorption of calcium in GI
tract
Skin wound healing
• skin damage sets in motion a sequence
of events that repairs the skin to as
normal as it can in both structure &
function
• depending on depth of wound 1 of 2
processes occur
– epidemal wound healing
– deep wound healing
Epidermal wound healing
• abrasion: portion of skin has been
scraped away
• in response to injury: basal cells of nearby
uninjured skin break contact with bm, enlarge,
& migrate across the wound
– migration continues across wound until meet cells
advancing from other side of wound
– contact inhibition: cells stop migrating when touch
another cell
Deep wound healing
• when injury extends deeper than
epidermis repair process more complex
& scars form
• healing occurs in 4 phases:
1. Inflammatory phase
2. Migratory phase
3. Proliferative phase
4. Scar formation
Inflammatory phase
• blood clot forms
– loosely unites edges of wound
• inflammation develops
– vascular response
• vasodilation & increased permeability of vessels
– cellular response
• phagocytic WBCs (neutrophils), macrophages
• fibroblasts
Migratory phase
• clot  scab
• epithelial cells migrate beneath scab to
bridge wound
• fibroblasts begin secreting collagen &
glycoproteins  scar
• *tissue filling wound called granulation
tissue
Proliferative phase
• extensive growth of epithelial cells
beneath scab & deposition of collagen in
random patterns (fibroblasts)
• growth of blood vessels
Scar formation
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aka maturation phase
scab falls off
epidermis restored
collagen fibers become more organized
fibroblasts disappear
blood vessels restored to normal
scar tissue less elastic, fewer blood
vessels, +/- accessory structures of skin
Scar formation
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aka maturation phase
scab falls off
epidermis restored
collagen fibers become more organized
fibroblasts disappear
blood vessels restored to normal
scar tissue less elastic, fewer blood
vessels, +/- accessory structures of skin
burns
• tissue damage caused by excessive heat,
electricity, radioactivity, or corrosive
chemicals that denature proteins in skin
cells
• destroy skin’s ability to maintain
homeostasis
• graded by their severity: 1st & 2nd degree
= partial thickness burns; 3rd degree = full
thickness
1st degree burns
• only epidermis is damaged
• example: sunburn
• symptoms:
– localized redness, swelling, & pain
• tx: immediate flushing with cool water
(lessens pain)
• healing: 3 – 6 days +/- peeling of skin
• results: normal
2nd degree burn
• epidermis & upper dermis damaged, some
skin function lost, ass’c structures not
damaged
• symptoms:
– same as 1st degree + blisters (epidermis
separates from dermis due to accumulation of
tissue fluid)
• example: any burn with blisters
2nd degree burns
• tx: if 2° infection: antibiotics
• lasts: 3 – 4 wks with +/- scarring
• AVOID: WEAR SUNSCREEN!
3rd degree burns
• destroys epidermis, dermis, & subQ
• no initial edema or pain or sensations
(receptors destroyed)
• most skin functions lost
• as healing starts  marked edema
• regeneration: months, + scarring
• tx: +/- skin grafting
Systemic effects of a burn
• greater threat to life than burn itself
• include:
1. large loss of water, plasma, plasma
proteins
2.
3.
4.
5.
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 shock
bacterial infection
reduced circulation of blood
decreased urine production
diminshed immune response
Major burns
• used to estimate extent & severity of
burns
• major burn considered a 3° burn that
covers > 10% of body or a 2° burn that
covers > 25% of surface area of body or
any 3° burn on face, hands, feet, or
perineum
• if burn > 70% surface area  > ½ patients
die
Skin cancer
• 3 common forms:
1. Basal cell carcinoma
2. Squamous cell carcinoma
3. Malignant melanoma
• 1 & 2 50% more common in males
Basal cell carcinoma
• > 78% all skin cancers
• arises in cells from stratum basale
– Sun-exposed areas
• rarely metastasizes.
Squamous cell carcinoma
• ~20% of all skin cancers
• arise from squamous cells in epidermis
• variable tendency to metastasize
Malignant melanoma
• arise from melanocytes
• ~2% of all skin cancers
• deadliest form of skin cancer
– spreads rapidly, can die w/in months of dx
• ~1/50 Americans will develop in their
lifetimes (was 1/500 in 1930’s)
– increase partly due to hole in ozone layer
(more UV rads)
– main reason: more people spend more time in
sun &/or tanning beds
Malignant melanoma
key to successful tx is early detection
early warning signs: ABCD
A: asymetrical lesion
B: borders are irregular
C: color is uneven; may have multiple
coloration
• D:diameter: ordinary moles <0.25 in
(pencil eraser)
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Development of the
integumentary system