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List and briefly describe the 4
types of cells commonly found in
the epidermis.

What type of tissue is the
Melanin – pigment of skin color
     Produced by melanocytes (usu. in stratum basale)
     Color is yellow to brown to black
     Amount depends upon genetics and exposure to sunlight
     Accumulates over nuclei of keratinocytes to prevent mutations

                                           Carotene and
                                            Hemoglobin can also
                                            contribute to skin color
    Skin Color can indicate Homeostatic Imbalance
                                  Addison’s disease –
 Cyanosis (blue) – poorly         hyposectretion of cortex
  oxygenated blood                 hormones
 Redness – embarrassment,            Bronze skin tone, weak
  fever, hypertension, allergy         muscles, burnout from
 Pallor – hypotension, fear,          stress, susceptibility to
  anger                                infection

 Jaundice – yellow cast =
  possible liver disorder
 Bruises - clot beneath skin
Dermis – deep to epidermis: 2 layers
 Papillary layer (upper dermal
  region, areolar CT)
     Projections called
      dermal papillae                  Epidermal Pegs
         Capillary loops,
          pressure and pain
 Reticular layer (deepest skin
  layer, dense irregular CT)
     Blood vessels
     Sweat and oil glands
     Deep pressure receptors
    Nerve Structure of Skin (exteroceptors)
 Papillary layer:
         Light touch - Meissner’s corpuscles, Merkel discs
         Pain receptors, too!

Reticular layer:
Pacinian Corpuscles
– deep pressure

Nerve endings around
hair follicles detect
wind, insects - eek

                                                             Figure 4.4
Dermis = our ‘hide’ (leather)
Collagen fibers = toughness        from age/smoking
Elastic fibers = elasticity
                                      = wrinkles
Temperature control: Blood
  vessels fill to cool; empty to
  retain heat
Hypodermis (subcutaneous layer) = adipose tissue

 Not officially part
  of the skin
 Lots of blood
  vessels – good
  spot for injections
 Primary storage
  site for fat/weight
Skin Appendages
 Cutaneous glands = exocrine glands
    Sebaceous glands – secrete oil (holocrine)
    Sweat glands – sweat (merocrine)
Sebaceous Glands – usu. empty into hair follicles
   Produce oil – activated at puberty
      Lubricant for skin                 Acne = plugged oil
                                            glands due to
      Prevents brittle hair
                                          bacterial infection
      Kills bacteria! – we’re toxic!

                            Plugged sebaceous gland
                                 = PIMPLE!
 Sweat Glands – 4 types              Ceruminous glands – modified
                                      apocrine glands in ear canal that
                                      secrete cerumen (wax)
 Eccrine                            Mammary glands – specialized
    Open onto skin surface,          sweat glands that secrete milk
     most common (2.5 million
     per person)
 Apocrine
    Empty into hair follicles,
     activated at puberty
    Axillary and Genital regions
    Includes extra protein &
     lipids that nourish bacteria
     and cause odors, i.e. B.O.
Sweat and Its Function
 Composition
    Mostly water (99%)
    Salts, vitamin C, dermicidin
    Some metabolic waste
    pH 4-6 usually
 Function
    Dissipate excess heat
    Excretes waste
    Inhibits bacteria

Describe 2 ways the skin helps to moderate body temperature.
Hair – an appendage of the skin

 Produced by hair
 Consists of keratinized
  epithelial cells
 Melanocytes provide
 Hair and Hair Follicles
 Hair bulb – deep end of follicle,
  wrapped by sensory nerve (hair
  follicle receptor)
 Hair root – hair below skin,
  gradually hardens to form shaft
 Hair shaft – mature hair above
  skin, dead keratinized cells with
  outer cuticle

                                      Figure 4.7c
Arrector pili – smooth muscle attached to follicle
and papillary layer cause ‘goosebumps’
 Root sheath – infolding of
  epidermal and dermal layers     Hair Follicle
  surrounding root
     Glassy membrane =
      basement membrane of
      follicle (ET to CT)
 Hair matrix – single layer of
  ET that actively divides to
  produce the hair (homologue
  to stratum basale)
     Stratum basale
 Hair papilla – vascularized
  nipple of dermal CT provides
  nourishment for matrix
     Dermal papilla

                                        Figure 5.5c
Hair Growth depends mostly on nutrition and hormones
 2 hair types = vellus (thin, lack medulla,
  body hair of children, adult females) and
  terminal (coarse, longer hair of scalp,
  eyebrows, etc.)
 Hormonal control by androgens (male sex
 Growth averages 2.5mm/week and length
  determined by active growth phases
    Scalp active for 6-10 years
    Eyebrows 3-4 months                        Alopecia – gradual
 Resting phase = 1-3 months, hair lost or     decline in hair growth
  pushed out by new active phase                  rates with age

                                                              Figure 5.5a
Nails – heavily keratinized modifications of
   Stratum basale in nail matrix responsible for
    growth, nail itself is mostly dead cells of hard
    keratin (like hair)

a. Ultimately, all epidermal cells
including hair and nail cells come
from the __________ layer of the

b. What layer of the skin delivers
nutrients to the above mentioned
epidermal layer?

  a. Stratum basale

  b. dermis or papillary layer
Functions of the Integumentary System
 Protection – chemical, physical, and mechanical barrier
     Chemical – acid mantle, antibiotics, melanin
     Physical/mechanical – keratin, glycolipids (lipid soluble
      compounds, salts of heavy metals can get through)
 Body temperature regulation is accomplished by:
     Dilation (cooling) and constriction (warming) of dermal vessels
     Increasing sweat gland secretions to cool the body
 Cutaneous sensation – exoreceptors sense touch and pain
Functions of the Integumentary System
  Metabolic functions – synthesis of vitamin D in dermal blood
  Blood reservoir – skin blood vessels store up to 5% of the
   body’s blood volume
  Excretion – limited amounts of nitrogenous wastes are
   eliminated from the body in sweat
   Burns – damage from heat, electricity, UV, chemicals

 Severe Burns = catastrophic
  fluid loss (dehydration,
  electrolyte imbalance), possible
  shock (infections after 24 hrs)
 Rule of 9’s: estimate of burn
Severity of Burns
 First-degree burns
     Epidermis only
     Red and swollen (typical sunburn)
 Second-degree burns
     Epidermis and upper dermis damaged
     Red with blisters
 Third-degree burns
     Entire skin layer destroyed
     Burn is gray-white or black
  Critical Burns
 >25% of body = 2° burns
 >10% of body = 3° burns
 3° burns to face, hands, or
While attempting to leap over a
campfire to impress his friends,
crazy Uncle Bob trips and
manages to receive 2nd degree
burns to the anterior sides of both
legs. What percentage of his body
is burned?
 9% anterior + 9% posterior = 18%

Would uncle Bob’s burns be
considered critical?

       Less than 25% 2° =
      nope, but jumping fires
      still not recommended
  Skin Cancer – uncontrolled cell division in skin
              Skin cancer = #1 cancer
 Basal cell carcinoma – least malignant, most common,
  (stratum basale)
 Squamous cell carcinoma – easy cure early, but does
  metastasize to lymph nodes, (stratum spinosum)
 Malignant melanoma – most deadly, rapid metastasis to
  lymph and blood, (melanocytes)
ABCD Rule: detecting malignant melanoma
 A = Asymmetry – opposite sides don’t match
 B = Border irregularity – borders not smooth
 C = Color – one mole, several colors
 D = Diameter - >6mm (pencil eraser)
Skin Infections (loss of homeostasis)
    Cold sores – virus
    Impetigo – bacteria
    Psoriasis – unknown (trauma, infection, stress =
More infections and 1 allergy!
    Contact dermatitis - allergy
    Athlete’s foot (tinea pedis) - fungus
    Boils and carbuncles - bacteria

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