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					Integumentary System
• Skin – the body’s largest organ
• Accounts for 15% of the body weight
• Consists of two layers – epidermis and dermis
• Mostly 1 – 2 mm thick but ranges with
• Difference mainly related to the thickness of
  the dermis
• Classified as thick or thin based on the relative
  thickness of the epidermis alone
• Thick skin – covers palms, soles, and
  corresponding surfaces of the fingers and toes
• Epidermis – about 0.5 mm thick because of a
  very thick surface of dead cells called the stratum
• Has sweat glands but no hair follicles or
  sebaceous glands
• Thin skin – covers the rest of the body
• Epidermis – about 0.1 mm thick with a thin
  stratum corneum
• Has hair follicles, sebaceous glands, and sweat
• Functions of the skin

•   Resistance to trauma and infection
•   Other barrier functions
•   Vitamin D synthesis
•   Sensation
•   Thermoregulation
•   Social functions
• Epidermis

• Keratinized stratified squamous epithelium
• Surface with dead cells packed with protein
  called keratin
• Lacks blood vessels and depends on diffusion
  of nutrients from underlying dermis
• Sparse nerve endings
• Most sensations in the skin due to nerve
  endings in the dermis
• Cells of the Epidermis – five types

• Stem cells – undifferentiated cells that undergo
  mitosis – give rise to keratinocytes – found in the
  deepest layer of epidermis which is the stratum
• Keratinocytes – great majority of epidermal cells
  – almost all cells seen on a slide are keratinocytes
• Melanocytes – Occur in the stratum basale –
  synthesize black or brown melanin – branching
  processes that shed melanin fragments from
  their tips
• Tactile (Merkel) cells – found in the basal layer
  of the epidermis – few in number – receptors
  for the sense of touch – associated with an
  underlying dermal nerve – the cell and the
  nerve called a tactile (Merkel) disc
• Dendritic (Langerhans) cells – found in the
  stratum spinosum and the stratum
  granulosum – macrophages that originate in
  the bone marrow – migrate to the epidermis,
  oral cavity, vagina and esophagus – protect
  against toxins and microbes
• Layers of the epidermis – from youngest to

• Stratum basale – mainly a single layer of
  cuboidal or low columnar stem cells and
  keratinocytes resting on the basement
  membrane – melanocytes and tactile cells
  scattered among these – stem cells give rise to
  keratinocytes that migrate toward the surface
  and replace lost surface cells
• Stratum spinosum – several layers of
  keratinocytes – thickest layer in thin skin but
  stratum corneum thickest layer in thick skin -
  deepest layer still capable of mitosis – lose
  this ability as they move further upward –
  become flatter the higher up they go -
  keratinocytes with desmosomes and tight
• Stratum granulosum – three to four layers of
  flat keratinocytes – more in thick skin than in
  thin skin – cells contain keratohyalin
• Stratum lucidum – thin translucent zone
  superficial to the stratum granulosum – seen
  only in thick skin – keratinocytes densely
  packed with eleidin, which is important in the
  synthesis of keratin – cells have no nuclei or
  other organelles – indistinct cell borders
• Stratum corneum – up to thirty layers of dead
  keratinized cells – resistant to abrasion,
  penetration, and water loss
• Life history of a keratinocyte

• Keratinocytes are shoved upward by the
  dividing cells below.
• Cells grow flatter and they produce lipid filled
  membrane coating vesicles.
• In the stratum granulosum the keratinocytes
  undergo apoptosis.
• The keratohyalin granules release a substance
  that binds to the cytoskeleton and converts
  them to keratin.
• The membrane coating vesicles release a lipid
  mixture that spreads out over the cell surface
  and waterproofs it.
• An epidermal water barrier forms between
  the stratum granulosum and the stratum
• It consists of lipids secreted by the
  keratinocytes and tight junctions between the
• The epidermal water barrier is crucial to
  retaining water and preventing dehydration.
• Cells above the barrier die
• Therefore the stratum cornea consists of
  compact layers of dead keratinocytes.
• Dermis – ranges from 0.2 mm thick in the eyelids
  to 4 mm thick in the palms and soles – composed
  of collagen, elastic and reticular fibers – contains
  fibroblasts and all the cells usually found in fibrous
  connective tissue – contains blood vessels, sweat
  glands, sebaceous glands, nerve endings, hair
  follicles, and nail roots
• Smooth muscle (piloerector muscles) – associated
  with hair follicles – contract in response to cold,
  fear, and touch
• Skeletal muscle – attached to the dermis in the
  face and produces facial expressions
• Dermal papillae

• Epidermal ridges

• Friction ridges

• Dermis in sensitive areas
• Dermis –two layers

• Papillary layer – thin zone of areolar tissue in
  the dermal papillae – loosely organized tissue
  allows for mobility of leucocytes and other

• Reticular layer – deeper and much thicker –
  dense irregular connective tissue – thick
  bundles of collagen with less room for ground
  substance – striae or stretch marks caused by
  stretching of the skin tearing the collagen
• Hypodermis - also called subcutaneous tissue or
  superficial fascia
• Has areolar and fat tissue
• Binds the skin to the underlying tissue
• Medications are frequently injected into this area
  because of vascularity
• Subcutaneous fat – hypodermis composed mostly
  of adipose tissue – not uniformly distributed –
  absent in scalp but copious in breast, abdomen,
  hips and thighs – 8% thicker in women than in
  men – infants and the elderly have less fat and
  therefore cold intolerance
• Skin Color

• Melanin – most significant factor in skin color –
  produced by melanocytes – accumulates in the
  keratinocytes of the stratum basale and stratum
• Two forms of melanin – a brownish black
  eumelanin – a reddish yellow sulfur containing
  pigment known as pheomelanin
• Hemoglobin – skin redder in places where blood
  capillaries come close to surface such as the lips
• Carotene – yellow pigment acquired from egg
  yolks and yellow and orange vegetables –
  concentrated in stratum corneum, subcutaneous
  fat, and skin of the heel
• Abnormal skin colors

• Cyanosis – blueness in the skin from a
  deficiency of oxygen in the circulating blood
• Erythema – abnormal redness of the skin –
  occurs with exercise, hot weather, sunburn,
  anger and embarrassment – caused by
  increased blood flow in dilated cutaneous
  blood vessels or from pooling of red cells that
  have escaped from the capillaries
• Pallor – a pale color that occurs when there is
  so little blood flowing through the skin that
  white collagen shows through – seen in
  emotional stress, low blood pressure,
  circulatory shock, cold temperatures, severe
• Albinism – a genetic lack of melanin that
  results in white hair, pale skin and pink eyes –
  lack of tyrosinase which is needed to make
  melanin from tyrosine – autosomal recessive
• Jaundice – Yellowing of the skin and whites of
  the eyes secondary to high levels of bilirubin
  in the skin
• Bronzing – a golden brown skin color – seen in
  Addison disease which is adrenal insufficiency
• Hematoma – a mass of clotted blood seen
  through the skin – bruise – usually due to
  trauma – can be seen in clotting disorders
• Skin markings
• Friction ridges – from dermal papillae in the
  fingertips – fingerprints – formed during fetal
  life and remained unchanged for life – unique
  pattern for everyone – not even identical
  twins have the same fingerprints
• Flexion lines – lines on the flexor surfaces of
  the digits, palms, wrists, and elbows – mark
  sites where the skin folds during flexion of the
• Freckles – flat melanized patches that vary
  with heredity and sun exposure
• Moles – elevated patch of melanized skin -
• Hemangiomas – birthmarks – patches of
  discolored skin caused by benign tumors of
  the dermal capillaries – Capillary
  hemangiomas are bright red to purple, slightly
  swollen and usually disappear in childhood –
  Cavernous hemangiomas (port wine stain) are
  flat and last for life
• Hair and nails – accessory organs – composed
  of hard keratin – more compact than the soft
  keratin seen in the stratum corneum of the
• Pilus – hair is known as a pilus or plural pili –
  slender filament of keratinized cells that grows
  from an oblique tube in the skin called a hair
• Three types of hair
• Lanugo hair – fine unpigmented hair that
  appears on the fetus in the last 3 months –
  most of it replaced by vellus hair by the time
  of birth
• Vellus hair – fine unpigmented hair –
  constitutes two – thirds of the hair of women
  and one – tenth of the hair of men –
  constitutes all of the hair of children except
  the eyebrows, eyelashes, and hair of the scalp
• Terminal hair – longer, coarser, and pigmented
  – forms the eyebrows, eyelashes, and the
  scalp – after puberty it forms the axillary hair,
  pubic hair, male facial hair, and hair on the
  trunk and limbs
• Structure of the Hair and Follicles

• Three zones along its length
• Bulb – a swelling at the base where the hair
  originates in the dermis
• Root – the remainder of hair within the follicle
• Shaft – portion above the skin surface
• Dermal papilla – provides the hair with its sole
  source of nutrition
• Hair matrix – above the papilla – region of
  mitotically active cells – hair’s growth center – all
  cells higher up are dead
• Cross section of the hair

• Medulla – loosely arranged cells and air
  spaces found in thick hairs but absent in thin
• Cortex – a layer of keratinized cuboidal cells
• Cuticle – a surface layer of scaley cells
• Hair follicle – a diagonal tube that dips deep into
  the dermis
• Epithelial root sheath – extension of the
• Connective tissue root sheath – derived from the
• Hair receptors – nerve fibers associated with the
• Pilorector muscle – bundle of smooth muscle
  fibers that extend from dermal collagen fibers to
  the connective tissue root sheath – responds to
  cold, fear and other stimuli – controlled by
  sympathetic nervous system – make hair stand on
• Hair texture and growth
• Texture related to differences in cross–sectional
  shape – straight hair is round – wavy hair is oval
  – curly hair is flat
• Hair color – due to pigment granules in the cells
  of the cortex – brown and black hair have
  eumelanin – red hair has some eumelanin but a
  high concentration of pheomelanin – blond hair
  has a moderate amount of pheomelanin and
  only a small amount of eumelanin – gray and
  white hair have no melanin in the cortex and air
  in the medulla
• Hair Growth and Loss

•   Hair cycle – three phases
•   Anagen
•   Catagen
•   Telogen
•   Alopecia
•   Pattern baldness
•   Hirsutism
• Functions of Hair

• Mostly vestigial
• Scalp hair – helps to retain heat – protects
  from sunburn
• Guard hairs or vibrissae hairs - prevent
  foreign particles from entering the nose or
• Eyelashes – shield the eyes from windblown
• Eyebrows – keep sweat from getting into the
• Nails – clear hard derivatives of the stratum
  corneum – composed of very thin, dead,
  scaley cells densely packed together and filled
  with parallel fibers and hard keratin –
  distinguishing characteristic of primates –
• Growth – fingernails 1 mm per week and
  toenails slower – new cells added to nail plate
  by mitosis in the nail matrix at its proximal
• Cutaneous Glands
• Sweat glands or sudoiferous glands – two
• Merocrine or eccrine – most numerous -
  myoepithelial cells – insensible perspiration –
• Apocrine – occur in the groin, anal region,
  areola, and the beard area
• Sebaceous glands – produce sebum –
  holocrine glands with ducts that open into the
  hair follicle
• Ceruminous glands – found only in the
  external ear – forms earwax or cerumen –
  simple coiled tubular glands – ducts lead to
  skin surface – waterproofs auditory canal and
  has a bactericidal function
• Mammary glands – milk producing glands that
  develop within the female breast – prominent
  in pregnancy and lactation – modified
  apocrine sweat glands – produce a richer
  secretion and channel it through ducts to a
• Skin Cancer – induced by ultra violet rays of the
  sun – most often on the head and neck – most
  common in fair-skinned people and the elderly –
  very common cancer but easy to treat
• Basal cell carcinoma – most common type of skin
  cancer – least dangerous because it seldom
  metastasizes – arises from cells in the stratum
  basale and eventually invades the dermis
• Squamous cell carcinoma – arises from
  keratinocytes in the stratum spinosum – usually
  found on the scalp, ears, lower lip, or dorsum of
  the hand – chance of recovery is good with early
  detection and surgical removal – if neglected it
  can metastasize to lymph nodes and can be lethal
• Malignant melanoma – most deadly skin
  cancer – accounts for 5% of skin cancers –
  often arises from the melanocytes of a
  preexisting mole – metastasizes quickly and
  can be lethal – risk is greatest for people who
  experienced sunburn as children especially
  redheads – men have higher incidence of
  malignant melanoma than women – 70% of
  cases on malignant melanoma are associated
  with an oncogene BRAF - uncertain if the BRAF
  oncogene alone can cause malignant
• ABCD rule for recognizing malignant
• A for symmetry (one side of the lesion looks
  different than the other)
• B for border irregularity – scalloped
• C for color (often a mixture of brown and
  black sometimes red or blue)
• D for diameter (greater than 6mm)

• Treated by wide surgical excision
• UVA, UVB, Sunscreens
• Both can initiate skin cancer
• No such thing as a healthy suntan
• As the use of sunscreen has increased so has
  the incidence of skin cancer
• People who use sunscreen have a higher
  incidence of basal cell carcinoma than people
  who do not
• Some chemicals in sunscreen damage DNA
• Still not known if sunscreens are helpful or
• Burns – a leading cause of accidental deaths –
  fluid loss, infection and the toxic effects of eschar
• First degree burns – involve only the dermis –
  redness, slight edema and pain – heal in a few
  days – rarely leave a scar – sunburn
• Second degree burns – involve the epidermis and
  part of the dermis – may be red or blistered and
  painful – may take several weeks to heal and may
  leave a scar – epidermis regenerates by division
  of epithelial cells in the hair follicles and sweat
  glands and around the edges of the burn – bad
  sunburns and scalds
• Third degree burns – epidermis and dermis
  completely destroyed – epidermis can only
  regenerate from edges of the wound – often
  requires skin grafts
•   Management of burns
•   Fluid replacement
•   Antibiotics
•   Nutrition
•   Debridement
•   Skin grafts
•   Skin grafts
•   Autograft
•   Split thickness graft
•   Isograft
•   Allograft
•   Heterograft
•   Artificial skin
•   Immunosuppressants
• Interactions Between the Integumentary
  System and Other Organ Systems

• Skeletal system – skin in vitamin D synthesis
  promotes calcium absorption needed for bone
  growth and health – bone supports skin at
  scalp and other places
• Muscular system – vitamin D synthesis
  promotes calcium absorption needed for
  muscle contraction – skin dissipates heat
  generated by muscle – active muscles
  generate heat and warm skin – muscles
  contract and produce facial expression
• Nervous system – sensory impulses from skin
  transmitted to nervous system – nervous
  system regulates diameter of cutaneous
  vessels – stimulates perspiration – stimulates
  piloerector muscle
• Endocrine – Sex hormones cause changes in
  skin at puberty and menopause
• Circulatory system – dermal vasoconstriction
  diverts blood to other organs – skin prevents
  loss of fluid form cardiovascular system –
  vasoconstriction can increase blood flow –
  circulatory system delivers oxygen, nutrients
  and hormones to skin a carries away wastes
• Lymphatic system – skin detects foreign
  substances – lymphatic system controls fluid
  balance and prevents edema – immune cells
  protect skin from infection and promotes
  tissue repair
• Respiratory system – nasal hairs filter particles
  – respiratory system provides oxygen and
  removes carbon dioxide
• Urinary system – skin complements urinary
  system by excreting salts and some nitrogen
  wastes in sweat – urinary system maintains
  electrolyte and ph balance
• Digestive system – vitamin D synthesis
  promotes intestinal absorption of calcium –
  digestive system provides nutrients for skin
  development and function
• Reproductive system – cutaneous receptors
  respond to erotic stimuli – mammary glands
  produce milk – gonadal sex hormones
  promote growth and maturation of skin

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