The Integumentary System

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The Integumentary System

• Guaranteed to Last a Lifetime
• Chapter 5

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Integumentary System

• Integument (skin) and Accessory Organs
• Cutaneous Membrane (Skin) largest organ
• - epidermis
• - dermis
• Accessory Organs derive from epithelial cells
  of the epidermis but all extend into the dermis
• - sweat glands and sebaceous (oil) glands
• - hair follicles
• - nails
• Hypodermis has similar functions as skin
• - fatty layer deep to the skin
• - connects skin to underlying organs

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Skin Structure
Figure 5.1
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Skin and Underlying Tissues

• 7 of total body weight
• 1.5 4 mm thick
• 2 distinct regions
• - epidermis, superficial thick epithelial
  tissue
• - dermis, fibrous CT deep to the epidermis
• Deep to the skin is the hypodermis
• - composed of loose areolar CT and adipose
  tissue

Figure 5.2
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Functions of The Skin

• Helps the body to maintain homeostasis
• Protection against environmental hazards
• Thermoregulation
• Synthesis and storage of lipid reserves
• Synthesis of vitamin D
• Excretion (urea, salts, water)
• Sensory information
• Coordination of immune response

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LE 4-1
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Epidermis

• Consists of keratinized stratified squamous
  epithelium
• 4 distinct cell types
• keratinocytes, melanocytes, Merkel cells, and
  Langerhans cells
• Layers of the Epidermis (from superficial to
  deep)
• - Stratum corneum
• - Stratum lucidum (only in thick skin)
• - Stratum granulosum
• - Stratum spinosum
• - Stratum basale

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Layers of the Epidermis
Figure 5.3
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Thick vs Thin Skin 5 layers vs 4 layers or
strata (bed sheets)
Fig 5.4
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Epidermal Cells

• Keratinocytes produce keratin, a tough fibrous
  protein
• - provides physical and mechanical protection
• - produces antibiotics and enzymes that detoxify
  harmful chemicals
• - undergoes almost continuous mitosis
• Melanocytes produce the skin pigment melanin
  (black)
• - made in granules and transferred to nearby
  keratinocytes
• - cluster on the superficial side of
  keratinocytes (between incoming radiation and
  cell nuclei) shielding the cells DNA from UV
  rays
• - digested by lysosomes in light-skinned people
• - secretes signaling moleules in response to UV
  radiation that act to modulate the skins immune
  and inflammatory responses
• Merkel cells hemisphere-shaped cells sensitive
  to touch
• - when compressed release chemicals that
  stimulate disclike sensory nerve endings (touch
  receptor)
• Langerhans cells star-shaped dendritic type
  cells
• - take up pathogens by receptor-mediated
  endocytosis
• - travel to a nearby lymph node to initiate an
  antigenic immune response

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Stratum Basale (Basal Layer)

• Aka the stratum germinativum (germinating
  layer) - the deepest
• epidermal layer firmly attached to the underlying
  dermis
• Consists of a single row of cells mostly young
  keratinocytes (stem cells)
• - as these cells are pushed up by production of
  new cells beneath them they make the keratin that
  eventually fills their cytoplasm
• - when they reach the skin surface they are
  dead, flat sacs of keratin
• Merkel cells are distributed sparsely among the
  keratinocytes - associate with disclike sensory
  nerve ending
• 10-25 of the cells are spider-shaped melanocytes
  (melanin cells)

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Stratum Spinosum (Spiny Layer)

• Name is derived from spinelike extensions of its
  keratinocytes
• (artifact created during tissue preparation)
• Several cell layers thick
• Lower rate of mitosis than in the basal layer
• Contain thick bundles of intermediate filaments
• - tonofilaments (tension filaments) that
  contain pre-keratin (tension-resisting protein)
• Langerhans cells - scattered among the
  keratinocytes
• - initiate an immune response to all foreign
  cells that carry a foreign antigen (lymphocyte
  activation)

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Stratum Granulosum (Granular Layer)

• Thin layer with many granules
• Composed of 1 to 5 layers of flattened
  keratinocytes
• Contain abundant tonofilaments
• Contain granules - keratohyalin and lamellated
  (plated)
• - keratohyalin granules help form keratin in the
  more superficial layers
• - lamellated granules contain a waterproof
  glycolipid that is secreted into the
  extracellular space (slows water loss across the
  epidermis)
• PM of the cells thicken to become more resistant
• Epidermal cells in the layers above the stratum
  granulosum,
• are too far from the dermal (underlying CT)
  capillaries to
• receive nourishment

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Stratum Lucidum (Clear Layer)

• Aka the transition zone
• Occurs only in thick skin
• In light microscopy appears as a thin translucent
  band
• Consists of a few rows of flat, dead
  keratinocytes
• - electron microscopy reveals these cells are
  identical to the next layer

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Stratum Corneum (Horny Layer)

• Most external (superficial) layer of the
  epidermis
• Many cells thick and much thicker than in thin
  skin
• Dead keratinocytes are completely filled with
  keratin
• - upon death their nuclei and organelles
  disintegrated
• Keratin consists of tonofilaments embedded in a
  glue from the keratohyalin granules
• - both the keratin and the cells thickened PMs
  protect skin against abrasion and penetration
• Waterproof layer due to the glycolipid between
  the cells
• Cells are referred to as cornified or horny
  (cornu horn)
• - they are the dandruff shed from the scalp and
  flakes from dry skin
• - an average person sheds 18 kg (40 lbs) in a
  lifetime

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The Dermis

• The 2nd major layer of the skin is a strong
  flexible CT that binds
• the entire body together
• Consists of 2 layers the papillary and
  reticular layers
• Cell types fibroblast, macrophages, mast cells,
  and scattered WBCs
• Fiber types collagen, elastic, and reticular
• Richly supplied with nerve fibers and BVs

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Dermal BVs

• 2 vascular plexuses -network of converging
  diverging vessels
• Deeper cutaneous plexus (between hypodermis and
  dermis)
• - nourishes the hypodermis and the structures
  within the deeper portions of the dermis
• More superficial subpapillary plexus (below
  dermal papillae)
• - supplies more superficial dermal structures,
  the dermal papillae and the epidermis
• Dermal BVs play a critical role in
  thermoregulation
• - BVs are extensive and can hold 5 of all blood
  in the body
• - if internal organs need more blood or heat,
  nerves stimulate dermal vessels to constrict
  shunting more blood into the general circulation
• - on hot days dermal vessels engorge with warm
  blood, cooling the body by radiating heat away
  from it

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Papillary Dermal Layer

• Papillary layer superficial 20 of the dermis
• Composed of areolar CT with thin collagen
  elastic fibers
• Papillae (nipples), fingerlike projections that
  extend into the overlying epidermis
• - increases surface area for exchange of gases,
  nutrients, and waste products between the dermal
  layers
• - avascular epidermis depends on the diffusion
  of these materials
• - interdigitation strengthens the
  dermal-epidermal junction reducing blister
  formation
• Contains dermal ridges papillae lie atop of
  these mounds
• - elevates overlying epidermis into epidermal
  ridges (friction ridges) create fingerprints,
  palmprints, and footprints
• - increases friction, enhances gripping ability
  of the hands and feet
• - patterns are unique and genetically determined
• - sweat pores, open along crests of epidermal
  ridges leave distinct fingerprints

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Reticular Dermal Layer

• Deeper reticulum (network) layer accounts for
  80 of the
• dermis thickness
• Consists of dense irregular CT
• ECM has thick bundles of interlaced collagen
  elastic fibers
• - named for its networks of collagen fibers
• Lines of cleavage or tension lines
• - separation formed by less dense regions
  between collagen bundles
• - invisible lines occur over the entire body
  important that surgeons make incisions parallel
  to these lines
• Collagen fibers give skin its strenth and
  resilience
• Elastic fibers provide stretch-recoil properties
• - extreme stretching results in striae
  (streaks)
• Flexure lines, markings from the deep part of the
  dermis

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Flexure lines form as a result of a continual
folding of the skin, often over joints, where the
dermis attaches tightly to underlying structures
(palm, wrist, soles, fingers, and toes)
Figure 5.5
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Hypodermis (below the skin)

• Fatty hypodermis deep to the skin aka the
  superficial
• fascia subcutaneous (below the skin) layer
• Consists of both areolar and adipose CT
• Stores fat
• Anchors skin to underlying structures (mostly
  muscle)
• - but allows skin to slide relatively freely
• Insulator fat a poor conductor of heat prevents
  heat loss from the body
• Thickens with weight gain
• - accumulates 1st in the thighs and breasts of
  ?s
• - in ?s accumulates in the anterior abdomen
  (beer belly)

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Skin Color

• 3 pigments melanin, carotene, hemoglobin
• Melanin, most important - tyrosine (tyrosinase)
• - ranges from yellow to reddish to brown to
  black
• Carotene, yellow-orange pigment - vegetables
• - accumulates in the epidermis stratum corneum
  and in the fat of the hypodermis
• Pink hue - oxygenated hemoglobin
• - from capillaries of the dermis
• - Caucasian skin contains little melanin allows
  color of blood to show
• - bruising reflects sites where blood escaped
  from the circulation and clotted below the skin
• Hematoma (blood swelling), clotted mass of
  escaped blood

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Abnormal Skin Colors

• Cyanosis bluish color
• Erythremia abnormal redness
• Jaundice yellowish color
• Pallor pale or ashen color
• Albinism pale skin, white hair, pink eyes
• Hematoma black blue bruise

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Nails

• Superficial keratinized layers of the epidermis
• Has a distal free edge, a body, and a root rests
  on a epidermal nail bed
• Pink color due to rich network of capillaries in
  the underlying dermis

Figure 5.6
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Hair

• Distributed all over the skin surface, except on
  palms, soles,
• nipples, and parts of external genitalia
• Main function - to sense touch
• Thermoregulation
• - scalp hair protects the head against direct
  sunlight on hot days and heat loss on cold days
• Consists of a flexible strand of dead,
  keratinized cells
• - hard keratin predominates in hair and nails
• 1) tougher and more durable 2) cells do not
  flake off
• Chief parts the root (embedded in the skin) and
  the shaft (projects above the skin surface)

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Hair Structure

• A hair shaft consists of 3 concentric layers
• Medulla (middle) central core of large cells
  and air sacs
• Cortex consists of several layers of flattened
  cells
• Cuticle a single layer of overlapping cells
• - most heavily keratinized provides strength and
  binding

Figure 5.7
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Hair Follicles

• Extend from the epidermal surface into the dermis
• Hair bulb expanded end of the follicle
• Hair follicle receptor or root hair plexus knot
  of sensory nerve endings
• CT papilla (hair papilla) dermal bit that
  protudes into the hair bulb contains a knot of
  capillaries
• Hair matrix epithelial cells in the hair bulb
• - proliferating cells that form the hair shaft
• Wall of a hair follicle is composed of
• - an outer CT root sheath (derived from the
  dermis)
• - inner epithelial root sheath (derived from the
  epidermis)
• Glassy membrane basement membrane of the
  follicle epithelium

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Arrector pili (raiser of the hair) muscle

• Bundle of smooth muscle cells associated with
  each follicle

Figure 5.7
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Scanning electron micrograph of a hair shaft
emerging from a follicle at the epidermal surface
Figure 5.8
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Types and Growth of Hair

• Vellus (vellwool,fleece) body hair, fine and
  short
• Terminal longer coarser scalp hair and hair
  that appears at puberty
• Androgens (testosterone) male sex hormone that
  influences terminal hair (face, chest, arms, and
  legs)

• Active follicle
• Resting follicle

Figure 5.9
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Sebaceous (greasy) Glands

• The skins oil glands
• Occur over entire body except palms and soles
• Simple alveolar glands with several alveoli
  openings into a single duct
• - alveoli filled with cells (no lumen) that
  produce sebum (animal fat)
• Holocrine secretion (holos whole)
• - central cells fill with oily lipids until they
  burst
• - empty sebum into the upper 1/3 of hair
  follicles
• - spread superficially to cover the skin
• - secretion stimulated by hormones, especially
  androgens
• Makes skin and hair oily and in addition
• - collects dirt, softens and lubricates hair and
  skin, prevents hair from becoming brittle, keeps
  epidermis from cracking
• - helps to slow water loss across the skin and
  kills bacteria

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Sebaceous Glands
Figure 5.10
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Sweat (sudoriferous) Glands

• Only mammals have sweat glands
• humans have gt 2.5 million over entire skin
  surface
• - produce about 500 ml of sweat per day (up to
  12L)
• Sweat - 1 a blood filtrate released by
  exocytosis
• - 99 water some salts (NaCl) and traces of
  metabolic wastes (urea, ammonia, uric acid)
• - acidic property retards growth of bacteria
• 2 types of sweat glands eccrine (secreting)
  aprocrine
• - both secrete in response to heat or stress
• - eccrine glands are more numerous and produce
  true sweat
• - aprocrine glands are mainly confined to the
  axillary, anal, and genital areas and produce
  viscous and sometimes a milky or yellow color
  secretion

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Sweat Glands

• Eccrine glands - most abundant
• on palms, soles, and forehead
• - coiled, secretory base in the deep dermis and
  hypodermis
• - duct opens at skin surface (pore)
• Note facial pores are openings of hair
• follicles
• Apocrine glands - function at
• puberty due to androgens
• - ducts open into hair follicles
• - involved in sexual signaling (pheromones)

Figure 5.10b
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Burns

• Tissue damage inflicted by heat, electricity,
  radiation,
• extreme friction, or chemical
• Immediate threat from serious burns loss of
  body fluids
• - severe inflammatory edema
• - dehydration leads to circulatory shock
• Followed by infection loss of skin barrier
• Classified by severity (depth) partial and
  full-thickness
• - 1st degree only epidermis is damaged
  (sunburn)
• - 2nd degree epidermis and upper part of the
  dermis (blisters)
• - 3rd degree epidermis, dermis, hypodermis
• Rule of Nines - divides the body into 11 regions
• - Critical burns 1) over 10 of the body has
  3rd degree burns 2) 25 of the body has 2nd
  degree burns 3) 3rd degree burns on the face,
  hands, or feet

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Burns Rule of Nines
Figure 5.11
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Skin Cancer

• Most common type of cancer, million new cases in
  US / year
• Highest risk factor overexposure to UV rays in
  sunlight
• Increased risk with use of indoor tanning
• 3 types of skin cancer
• - Basal Cell Carcinoma
• - Squamous Cell Carcinoma
• - Melanoma

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Squamous Cell Carcinoma
Basal Cell Carcinoma

• Least malignant most common (gt30 of all
  Caucasians)
• Cells of stratum basale proliferate, invading the
  dermis hypodermis
• Most common lesions are dome-shaped, shiny
  nodules on the face
• Nodules develop an ulcer
• Grows slowly, metastasis is rare
• 99 full cure by removal

• Arises from the keratinocytes of the stratum
  spinosum
• Scaly, irregular, reddened papule that grows
  rapidly
• Metastasis - if not removed
• Overall cure rate 99
• Treatment - radiation, surgery, skin creams with
  anticancer drugs

Figure 5.12
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Most DangerousMelanomaCancer of Melanocytes

• Only 1 of every 20 skin cancers
• Increasing by 3-8 / yr in US
• Often arises from existing moles
• Melanoma cells metastasize
• - into surrounding circulatory vessels
• Key to survival early detection
• - low survival chance mole gt4mm thick
• Resistant to chemotherapy and immunotherapy
• ABCD(E) rule
• Asymmetry 2 halves dont match Border
  irregularity indents / notches Color pigment
  spot, several colors
• Diameter - gt6mm
• Elevation above the skin surface

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The Skin Throughout Life

• Epidermis develops from embryonic ectoderm
• Dermis and hypodermis develop from mesoderm
• Melanocytes develop from neural crest cells (3
  months)
• In 5th and 6th months fetus covered with lanugo
  (wool/down)
• Shed by the 7th month when vellus hairs appear
• Birth skin covered with vernix caseosa (varnish
  of cheese)
• Adolescence, acne may appear, subsides in early
  adulthood
• Optimal appearance in 20s 30s
• - after skin shows harmful effects of continued
  environmental assaults
• - dermatitis become more common
• Photoaging
• - pigment spots liver spots
• - large amounts of melanin protect skin from
  photoaging

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Clinical Terms

• Alopecia
• Athletes Foot
• Boils and Carbuncles
• Cold Sores (Fever Blisters)
• Impetigo (an attack)
• Psoriasis (an itching)
• Vitiligo (blemish)