THE INTEGUMENTARY SYSTEM

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THE INTEGUMENTARY SYSTEM

• Complex set of organs that includes the skin and
  its derivatives (sweat and oil glands, hairs, and
  nails)
• Includes
• Nerves
• Blood vessels
• Muscles
• Major function protection

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THE SKIN

• Also called the integument, which simply means
  covering
• Epidermis
• The epidermis is a keratinized stratified
  squamous epithelium (epiupon)
• Outer most protective shield of the body
• Dermis
• Underlying epidermis
• Makes up bulk of skin
• Composed of
• Fibrous connective tissue
• Blood vessels
• Nutrients reach the epidermis by diffusion

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SKIN
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THE SKIN

• Hypodermis also called superficial fascia
• Subcutaneous tissue
• Deep to the skin
• Not really part of the skin but it shares some of
  the skins protective functions
• Superficial to the tough connective tissue
  wrapping (fascia) of the skeletal muscles
• Consists mostly of adipose tissue
• Stores fat
• Shock absorber
• insulation
• Anchors the skin to the underlying structures
  (muscles)
• Thickens as one gains weight
• Thighs
• Breast
• Beer belly

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SKIN
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Epidermis

• A keratinized stratified squamous epithelium
  consisting of four distinct cell types and four
  or five distinct layers
• Stratum Corneum
• Stratum Lucidum (thick skin)
• Stratum Granulosum
• Stratum Spinosum
• Stratum Basale

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Cells of the Epidermis

• Include
• Keratinocytes
• Melanocytes
• Merkel cells
• Langerhans cells

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EPIDERMIS
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Cells of the EpidermisKeratinocytes

• Produce keratin
• Fibrous protein that helps give the epidermis its
  protective properties
• Tightly connected to one another by desmosomes
  (cell junction composed of thickened plasma
  membranes joined by filaments)
• Arise in the deepest part of the epidermis from a
  layer of cells (stratum basale) that undergo
  almost continuous mitosis
• Cells pushed upward by the production of new
  cells beneath them
• By the time they reach the free surface of the
  skin, they are dead, scalelike structures that
  are little more than keratin-filled plasma
  membranes
• Millions rub off everyday giving us a totally new
  epidermis every 25 to 45 days
• Friction rubs them off (hands, etc)
• Persistent friction causes a thickening of the
  epidermis called a callus

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EPIDERMIS
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Cells of the EpidermisMelanocytes

• Spider shaped cells
• Found in the deepest layer of the epidermis
• Synthesize the pigment melanin (melanblack)
• Made and accumulated in membrane-bound granules
  (small. grainlike mass) called melanosomes
• Moved along actin filaments by motor proteins to
  the ends of the melanocytes processes (spider
  arms)
• From here they are taken up by the keratinocytes
• Accumulate on the superficial (sunny side) of the
  keratinocyte nucleus, forming a pigment shield
  that protects the nucleus from the damaging
  effects of ultraviolet (UV) radiation in sunlight

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EPIDERMIS
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Cells of the EpidermisLangerhans Cells

• Star-shaped
• Arise from bone marrow and migrate to the
  epidermis
• Also called epidermal dendritic cells
• Are macrophages (WBC) that help activate our
  immune system
• Their slender processes extend among the
  surrounding keratinocytes, forming a more or less
  continuous network

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EPIDERMIS
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Cells of the EpidermisMerkel Cells

• Present at the epidermal-dermal junction
• Saped like a spiky hemisphere
• Intimately associated with a disclike sensory
  nerve ending
• This combination is called a Merkel disc
• Functions as a sensory receptor for touch

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EPIDERMIS
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Layers of the Epidermis

• Variation in epidermal thickness determines if
  skin is thick or thin
• Thick skin covers palms, fingertips, and soles
  of the feet
• Five layers strata (bed sheets)
• Deep to superficial
• Stratum basale
• Stratum spinosum
• Stratum granulosum
• Stratum lucidum
• Stratum corneum
• Thin skin covers the rest of the body
• Stratum lucidum is absent and the other layers
  are thinner

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EPIDERMIS
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Layers of the EpidermisStratum Basale

• Deepest epidermal layer
• Attached to the underlying dermis along a wavy
  borderline
• Consists (mostly) of a single row of cells
  representing the youngest keratinocytes
• Many mitotic nuclei
• Reflects rapid cell division
• Alternate name stratum germinativum

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EPIDERMIS
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Layers of the EpidermisStratum Spinosum

• Spinosum (prickly)
• Several cell layers thick
• Cells contain a weblike system of intermediate
  filaments, which span their cytosol to attach to
  desmosomes
• These intermediate filaments consist mainly of
  tension-resisting bundles of prekeratin filaments
• Keratinocytes appear irregular (spiny) in shape,
  causing them to be called prickle cells
• Spines do not exist in the living cells
• They arise during tissue preparation when these
  cells shrink but their numerous desmosomes hold
  tight
• Scattered among the keratinocytes are
• Melanin granules
• Langerhans cells (highest concentration)

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EPIDERMIS
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Layers of the EpidermisStratum Granulosum

• Consist of 3-5 layers in which keratinocyte
  appearance changes drastically
• Cells flatten
• Nuclei and organelles begin to disintegrate
• They accumulate
• Keratohyaline granules
• Help to form keratin in the upper layers
• Lamellated granules
• Contain a waterproofing glycolipid that is spewed
  into the extracellular space and is a major
  factor in slowing water loss across the epidermis
• Cell membranes thicken
• Lipids coat the external membrane
• Above this layer the epidermal cells are too far
  from the dermal capillaries, so they die

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EPIDERMIS
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Layers of the EpidermisStratum Lucidum

• Thin translucent band
• Few rows of clear, flat, dead keratinocytes with
  indistinct boundaries
• Gummy substance of the keratohyaline granules
  clings to the keratin filaments in the cells,
  causing them to aggregate in parallel arrays
  (regular arrangement)
• Visible ONLY in THICK SKIN

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EPIDERMIS
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Layers of the EpidermisStratum Corneum

• Horny (hard, callous) layer
• 23-30 cell layers thick (3/4 of epidermis)
• Keratin and the thickened plasma membranes of
  cells protect the skin against abrasion and
  penetration
• Glycolipid between cells waterproofs this layer
• The stratum corneum (horny layer) is the
  outermost protective layer of the epidermis
  composed of a thick layer of dead keratinocytes

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EPIDERMIS
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SKIN
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EPIDERMIS
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Dermis

• Composed of strong, flexible connective tissue
• Its cells are typical of those found in any
  connective tissue proper
• Fibroblasts cells that form the fibers of
  connective tissue
• Macrophages protective cell capable of
  phagocytosis
• Mast cells immune cell that initiates
  inflammation
• White blood cells protection
• Its semifluid matrix is heavily embedded with
• Collagen strong, fibrous (threadlike) insoluble
  protein
• Elastin extracellular connective tissue protein
• Reticular fibers supporting framework tissue
• The dermis binds the entire body together like a
  body stocking
• It is your hide and corresponds exactly to animal
  hides used to make leather products
• Richly supplied with nerve fibers, blood vessels,
  and lymphatic vessels
• Major portions of hair follicles, as well as oil
  and sweat glands, are derived from epidermal
  tissue but reside in the dermis

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DermisTwo Layers

• 1.The thin, superficial papillary layer is highly
  vascularized areolar connective tissue containing
  a woven mat of collagen and elastin fibers
• Its superior surface is thrown into peglike
  projections called dermal papillae
  (papillnipple) that indent the overlaying
  epidermis
• Many contain
• Capillary loops
• Meissners corpuscles touch receptors
• Pain receptors

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SKIN
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DermisTwo Layers

• On the palms of the hands and soles of the feet,
  these papillae lie atop larger mounds called
  dermal ridges
• Which in turn cause the overlying epidermis to
  form epidermal ridges that increase friction and
  enhance the gripping ability of the fingers and
  feet
• Epidermal ridge patterns are genetically
  determined and unique to each of us
• Because sweat pores open along their crest, our
  fingerprints leave identifying films of sweat
  called fingerprints on almost anything they touch

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SKIN
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DermisTwo Layers

• Three types of skin markings
• Finger prints
• Cleavage lines
• Flexure lines

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DermisTwo Layers

• 2.The reticular layer
• Deeper
• Account for 80 of the thickness of the dermis
• Extracellular matrix contains thick bundles of
  interlacing fibers that run in various planes
• Most run parallel to the skin surface
• Less dense regions, between these bundles form
  cleavage, or tension lines
• Important to a surgeon
• Incision made parallel to these lines, the skin
  gapes less and heals more readily than when the
  incision is made across cleavage lines
• Collagen fibers give skin strength and resiliency
• Binds water, helping keep the skin hydrated
• Elastin fibers provide the stretch-recoil
  properties of skin

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SKIN
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DermisTwo Layers

• Flexure lines
• Dermal folds that occur at or near joints, where
  the dermis is tightly secured to deeper
  structures (notice the deep creases on your
  palms)
• Since the skin cannot slide easily to accommodate
  joint movement in such regions, the dermis folds
  and deep skin creases form
• Visible on wrists, fingers, soles, and toes

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HOMEOSTATIC IMBALANCE

• Dermal tearing
• Stretching of the skin during pregnancy
• Stretch marks
• Blister
• Separation of the epidermal and dermal layers by
  a fluid-filled pocket

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Skin Color

• Determined by three pigments
• Melanin
• Hemoglobin
• Carotene

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Melanin

• Only pigment made in the skin
• Polymer of tyrosine amino acid
• Ranges in color from yellow to reddish-brown to
  black
• Synthesis depends on an enzyme in melaocytes
  called tyrosinase
• Passes from melanocytes to the basal keratinocytes

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Melanin

• All humans have the same relative number of
  melanocytes
• Individual and racial differences in skin
  coloring reflect the relative kind and amount of
  melanin made and retained
• Melanocytes of black and brown skinned people
  produce many and darker melanosomes than those of
  fair-skinned individuals, and their keratinocytes
  retain it longer
• Freckles and pigmented moles are local
  accumulations of melanin

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Melanin

• Melanocytes are stimulated by sunlight
• Causes substantial melanin buildup, which helps
  protect the DNA of viable skin cells from UV
  radiation by absorbing the light and dissipating
  the energy as heat

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HOMEOSTATIC IMBALANCE

• Excessive sunlight damages the skin
• Clumping of elastin fibers results in leathery
  skin
• Depresses the immune system
• Alters DNA

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Carotene

• Yellow to orange pigment found in certain plant
  products such as carrots
• Tends to accumulate in the stratum corneum and in
  the tissue of the hypodermis
• Color most obvious in the palms and soles, where
  the stratum corneum is thickest (example the
  skin of the heel)
• Most intense when large amounts of carotene-rich
  foods are eaten

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Hemoglobin

• Pinkish hue of fair skin people

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Skin Color Variations

• Redness erythema
• Embarrassment
• Fever
• Hypertension
• Inflammation
• Allergy
• Pallor blanching
• Fear
• Anger
• Emotional stress
• Anemia
• Low blood pressure

• Jaundice yellow cast
• Liver disorder (yellow bile pigment accumulates
  in the blood and deposited in body tissues)
• Bile normally secreted in the bile pigments
  (bilirubin) as part of bile
• Bronzing
• Metallic appearance of skin
• Addisons disease
• Hyperfunction of adrenal cortex
• Black and blue bruises
• Blood escaping from the blood vessels and
  clotting under the skin

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APPENDAGES OF THE SKIN

• Derivatives of the epidermis
• Sweat Glands
• Sebaceous Glands
• Nails
• Hair
• Hair Follicles

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Sweat (Sudoriferous) Glands

• Distributed over the entire skin surface except
  the nipples and parts of the external genitalia
• Two types of sweat glands
• Eccrine
• Apocrine

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Sweat (Sudoriferous) GlandsEccrine Sweat Glands

• (b)Eccrine sweat glands, or merocrine sweat
  glands, produce true sweat, are the most numerous
  of the sweat glands, and are particularly
  abundant on the palms of the hands, soles of the
  feet, and forehead

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CUTANEOUS GLANDS
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CUTANEOUS GLANDS
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Sweat (Sudoriferous) GlandsEccrine Sweat Glands

• Also called merocrine sweat glands
• Abundant on the palms, soles of feet, and
  forehead
• Simple, coiled, tubular gland Secretory part lies
  coiled in the dermis
• The duct extends to open in a funnel-shaped pore
  at the skin surface
• Secretion commonly called sweat is a
• Hypotonic filtrate (lower osmotic pressure than a
  reference) of the blood that passes through the
  secretary cells of the sweat glands and is
  released by exocytosis
• 99 water, with some salts (mostly sodium
  chloride)
• Vitamin C
• Antibodies
• Dermicidin microbe-killing peptide
• Traces of metabolic waste ( urea, uric acid,
  ammonia)
• Lactic acid chemical that attracts mosquitoes
• pH between 4-6

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Sweat (Sudoriferous) GlandsEccrine Sweat Glands

• Sweating is regulated by the sympathetic nervous
  system
• Major role is to prevent overheating of the body
• Heat-induced sweating begins on the forehead and
  then spreads inferiorly over the remainder of the
  body
• Emotionally induced sweatingso-called cold
  sweat brought on by fright, embarrassment, or
  nervousnessbegins on the palms, soles, and
  axillae (armpits) and then spreads to other body
  areas

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Sweat (Sudoriferous) GlandsApocrine Sweat Glands

• Largely confined to the axillary and anogenital
  areas
• Larger than eccrine glands
• Ducts empty into hair follicles
• Secretion contains the same basic components as
  true sweat, plus fatty substances and proteins
• Quite viscous and milky or yellowish color
• Odorless
• BUT, when its organic molecules are decomposed by
  bacteria on the skin, it takes on a musky and
  generally unpleasant odor (BODY ODOR)

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Sweat (Sudoriferous) GlandsApocrine Sweat Glands

• Little role in thermoregulation
• Role not completely understood
• BUT, they are activated by sympathetic nerve
  fibers during pain and stress
• Because their activity is increased by sexual
  foreplay, and they enlarge and recede with the
  phases of a womens menstrual cycle, they may be
  analogous to the sexual scent glands of other
  animals

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Sweat (Sudoriferous) GlandsCeruminous Glands

• Modified apocrine glands found in the lining of
  the external ear canal
• Secrete a sticky, bitter substance called
  cerumen, or earwax
• Thought to deter insects and block entry of
  foreign material

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Sweat (Sudoriferous) GlandsMammary Glands

• Variety of modified sweat glands in the breasts
  that secrete milk

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Sebaceous (Oil) Glands

• Sebaceous glands are simple alveolar glands (c)
  found all over the body except the palms of the
  hands and soles of the feet

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EXOCRINE GLANDS
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Sebaceous (Oil) Glands

• Secrete sebum, an oily secretion
• The central cells of the alveoli accumulate oily
  lipids until they become so engorged that they
  burst, so functionally these glands are holocrine
  glands
• The entire secretory cell ruptures, releasing
  secretions and dead cell fragments
• Secreting their product into a hair follicle or
  to a pore on the surface of the skin
• Sebum softens and lubricates the hair and skin,
  prevents hair from becoming brittle, and slows
  water loss from the skin when the external
  humidity is low
• Bactericidal action (bacterium-killing)

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Holocrine Gland
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Sebaceous (Oil) Glands (a)

• Secretion is stimulated by hormones, especially
  androgens

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CUTANEOUS GLANDS
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Sebaceous (Oil) Gland
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HOMEOSTATIC IMBALANCE

• If a sebaceous gland duct is blocked by
  accumulated sebum, a whitehead appears on the
  skin surface
• If the material oxidizes and dries, it darkens to
  form a blackhead
• Acne is an active inflammation of the sebaceous
  glands accompanied by pimples (pustules or
  cysts) on the skin
• Usually caused by bacterial infection,
  particularly by staphylococcus
• Seborrhea cradle cap in infants
• Caused by overactive sebaceous glands
• Raised lesions that gradually become yellow to
  brown and begin to slough off oily scales

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Nails

• A nail is a scalelike modification of the
  epidermis that forms a clear, protective covering
  on the dorsal surface of the distal part of a
  finger or toe
• Nails are made up of hard keratin
• Each nail has a free edge, a body (visible
  attached portion), and a proximal root (embedded
  in the skin)
• The deeper layers of the epidermis extend beneath
  the nail as the nail bed
• Corresponds to the superficial keratinized layers
• The thicker proximal portion of the nail bed,
  called the nail matrix, is responsible for nail
  growth

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NAIL
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Nails

• Nails normally appear pink because of the rich
  bed of capillaries in the underlying dermis
• Region that lies over the thick nail matrix
  appears as a white crescent called the lunula
  (little moon)
• Proximal and lateral borders of the nail are
  overlapped by skin folds, called nail folds
• Proximal nail fold projects onto the nail body as
  the cuticle (eponychiumon the nail)
• Region beneath the free edge of the nail where
  dirt and debris tend to accumulate is the
  hyponychium (below nail), informally called the
  quick

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Structure of a Hair

• Hairs, or pili, are flexible strands produced by
  hair follicles that consist largely of dead,
  keratinized cells
• The hard keratin that dominates hairs and nails
  has two advantages over the soft keratin found in
  typical epidermal cells
• 1. It is tougher and more durable
• 2. Its individual cells do not flake off

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Structure of a Hair

• The main regions of a hair are the shaft, which
  projects from the skin, and the root, the part
  embedded in the skin

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HAIR SHAFT
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HAIR
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Structure of a Hair

• If the shaft is flat and ribbonlike in cross
  section, the hair is kinky
• If the shaft is oval in cross section, the hair
  is silky and wavy
• If the shaft is perfectly round in cross section,
  the hair is straight and tends to be coarse

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Structure of a Hair

• A hair has three layers of keratinized cells
• Inner core (central core) is the medulla
• Consist of large cells and air spaces
• Absent in fine hair
• Middle layer is the cortex
• Bulky layer surrounding the medulla, consists of
  several layers of flattened cells
• Outer layer is the cuticle

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HAIR
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Structure of a HairCuticle

• Formed from a single layer of cells that overlap
  one another from below like shingles on a roof
• This arrangement helps to keep neighboring hairs
  apart so that the hair does not mat
• Hair conditioners smooth out the rough surface of
  the cuticle and make our hair look shiny
• The most heavily keratinized part of the hair,
  the cuticle, provides strength and helps keep the
  inner layers tightly compacted
• It is subjected to the most abrasion, the cuticle
  tends to wear away at the tip of the hair shaft,
  allowing the keratin fibrils in the cortex and
  medulla to frizz out, creating split ends

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HAIR SHAFT
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Structure of a Hair

• Hair pigments (melanin of different colors) are
  made by melanocytes at the base of the hair
  follicle and transferred to the cortical cells
• Various proportions of melanins of different
  colors (yellow, rust, brown, and black) combine
  to produce hair color from blond to pitch black
• Red hair is colored by the iron-containing
  pigment called trichosiderin
• Gray or white hair results from decreased melanin
  production (mediated by delayed-action genes) and
  from the replacement of melanin by air bubbles in
  the hair shaft (AIRHEAD-JOKE)

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Structure of a Hair Follicle

• Hair follicles fold down from the epidermis into
  the dermis and occasionally into the hypodermis
• The deep end of a hair follicle is expanded,
  forming a hair bulb, which is surrounded by a
  knot of sensory nerve endings called a hair
  follicle receptor, or root hair plexus, wraps
  around each hair bulb, and bending the hair
  stimulates these endings
• Consequently, our hairs act as sensitive touch
  receptors

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HAIR FOLLICLE
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SKIN
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Structure of a Hair Follicle

• Hair papilla, a nipplelike bit of dermal tissue,
  protrudes into the hair bulb
• Contains a knot of capillaries that supplies
  nutrients to the growing hair and signals it to
  grow
• The wall of a hair follicle is composed of
• Outer connective tissue root sheath, derived from
  the dermis,
• A thickened basement membrane called a glassy
  membrane,
• An inner epithelial root sheath, derived mainly
  from an invagination of the epidermis

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HAIR FOLLICLE
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SKIN
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Structure of a Hair Follicle

• Hair matrix actively dividing area of the hair
  bulb that produces the hair
• Associated with each hair follicle is a bundle of
  smooth muscle cells called an arrector pili
  muscle
• Most hair follicles approach the skin surface at
  a slight angle
• Arrector muscles are attached in such a way that
  their contraction pulls the hair follicle into an
  upright position and dimples the skin surface to
  produce goose bumps

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SKIN
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Types and Growth of Hair

• Hairs come in various sizes and shapes, but can
  be classified as
• Vellus vellwool, fleece
• Pale, fine body hair variety of children and
  adult females
• Terminal
• Darker
• Coarser, longer hair of eyebrows and scalp
• Axillary and pubic
• Face and chest of males
• Hair growth and density are influenced by many
  factors, such as nutrition and hormones

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Types and Growth of Hair

• The rate of hair growth varies from one body
  region to another and with sex and age
• Averages 2.5 mm per week
• Life span of hairs varies and appears to be under
  control of a slew of proteins
• Each follicle has a growth cycle where it is
  active and inactive for a period of time
• Inactive, hair matrix cells die and the follicle
  base and hair bulb shrivel
• Follicle then enters a resting stage for a period
  of time
• After the resting phase, the matrix proliferates
  again and forms a new hair to replace the old one
  that has fallen out or will be pushed out by the
  new hair
• Only a small percentage of the hair follicles are
  shed at any one time, we lose an average of 90
  scalp hairs daily
• Follicles of the eyebrow hairs remain active for
  only 3-4 months, which explains why your eyebrows
  are never as long as the hairs on your head

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HOMEOSTATIC IMBALANCE

• In women, small amounts of androgens are normally
  produced by both the ovaries and the adrenal
  glands
• Excessive hairiness (hirsutism hirsuthairy)
• Signs of masculinization
• Large amounts of androgens can be secreted by
  ovarian tumors resulting in
• Beard and hairy chest
• Tumors can be surgically removed

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Hair Thinning and Baldness

• A follicle has only a limited number of cycles in
  it
• Ideal conditions, hair grows faster from the teen
  years to the 40s then its growth slows
• The fact that hairs are not replaced as fast as
  they are shed leads to hair thinning and some
  degree of baldness (alopecia), in both sexes
• Begins at the anterior hairline and progresses
  posteriorly
• Coarse terminal hairs are replaced by vellus
  hairs, and the hair becomes increasingly wispy
• Male pattern baldness, which is a type of true,
  or frank, balding, is a genetically determined,
  sex-influenced condition

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FUNCTIONS OF THEINTEGUMENTARY SYSTEM

• Protection
• 1.Chemical barriers include skin secretions and
  melanin
• Although the skins surface teems with bacteria,
  the low pH of skin secretions (acid mantle)
  retards their multiplication
• Many bacteria are killed by bactericidal
  substances in sebum
• Natural antibiotic (human defensin) kills
  bacteria
• Chemical pigment (melanin) prevents UV damage

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FUNCTIONS OF THEINTEGUMENTARY SYSTEM

• 2.Physical or mechanical barriers are provided by
  the continuity of the skin, and the hardness of
  the keratinized cells
• Waterproofing glycolipids block diffusion of
  water and water soluble substances between cells
  (preventing both loss and entry)
• Lipid soluble substances DO penetrate
• Oxygen, carbon dioxide
• Fat-soluble vitamins (A, D, E, K)
• Steriods
• Oleoresins (plants poison ivy and oak)
• Organic solvents (acetone, dry cleaning fluids,
  paint thinner)
• Causes kidney shut down and brain damage
• Salts of heavy metals (lead, mercury, nickel)
• Results in anemia and neurological defects
• Drug agents (penetration enhancers) that help
  ferry other drugs into the body

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FUNCTIONS OF THEINTEGUMENTARY SYSTEM

• 3.Biological barriers include
• Langerhans cells of the epidermis
• Active elements of the immune system
• Respond to antigens
• Macrophages of the dermis
• Dispose of viruses and bacteria that have managed
  to penetrate the epidermis
• DNA itself
• Absorb UV radiation and transfer it to the atomic
  nuclei, which heat up and vibrate vigorously
• Heat dissipates to surrounding water molecules
  instantaneously, the DNA converts potentially
  destructive radiation into harmless heat

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Body Temperature Regulation

• The skin plays an important role in body
  temperature regulation by
• Using the sweat glands of the skin to cool the
  body
• Evaporation of sweat from the skin surface
  dissipates body heat and efficiently cools the
  body, thus preventing overheating
• Constriction of dermal capillaries to prevent
  heat loss
• When the external environment is cold, dermal
  blood vessels constrict causing the warm blood to
  bypass the skin temporarily and allows the skin
  temperature to drop to that of the external
  environment
• Passive heat loss from the body is slowed, thus
  conserving body heat

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Cutaneous Sensation

• Made possible by the placement of cutaneous
  sensory receptors, which are part of the nervous
  system, in the layers of the skin
• Cutaneous receptors are classified as
  exteroceptors because they respond to stimuli
  arising outside the body
• Example
• Meissners corpuscles (in dermal papillae) and
  Merkel dics allow us to become aware of a caress
  or the feel of our clothing against our skin
• Pacinian receptors (in deepest dermis and
  hypodermis) alert us to bumps or contacts
  involving deep pressure
• Hair follicle receptors sense wind blowing
  through our hair and a playful tug on a pigtail
• Bare nerve endings that meander throughout the
  skin sense painful stimuli ( irritating chemical,
  extreme heat or cold, etc.)

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Metabolic Functions

• When sunlight bombards the skin, modified
  cholesterol molecules circulating through dermal
  blood vessels are converted to a vitamin D
  precursor, and transported via the blood to other
  body areas to play various roles in calcium
  metabolism
• Example calcium cannot be absorbed from the
  digestive tract without vitamin D
• Makes chemical conversions that supplement those
  of the liver
• Examples keratinocyte enzymes can
• 1. Disarm many cancer-causing chemicals that
  penetrate the epidermis
• 2. Convert some harmless chemicals into
  carcinogens
• 3. Activate some steroid hormones
• Transform cortisone applied to the skin into
  hydrocortisone, a potent anti-inflammatory drug
• Make several biologically important proteins,
  including collagenase, an enzyme that aids the
  natural turnover of collagen (deters wrinkles)

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Blood Reservoir

• Dermal vascular supply is extensive
• The skin may act as a blood reservoir by holding
  up to 5 of the bodys blood supply, which may be
  diverted to other areas of the body should the
  need arise
• When other body organs, such as vigorously
  working muscles, need a greater blood supply, the
  nervous system constricts the dermal blood
  vessels shunting more blood into the general
  circulation, making it available to the muscles
  and other body organs

100
Excretion

• Limited amounts of nitrogenous containing wastes
  (ammonia, urea, and uric acid) are eliminated
  from the body in sweat, although most nitrogenous
  wastes are excreted in urine
• Profuse sweating is an important avenue for water
  and salt (sodium chloride) loss

101
Skin Cancer

• Most tumors that arise in the skin are benign and
  do not spread (metastasize) to other body areas
• Example
• A wart a neoplasm (abnormal growth of tissue
  that serves no purpose but grows at the expense
  of healthy tissue) caused by a virus
• Some tumors are malignant, or cancerous, and
  invade other body areas
• A crucial risk factor for the nonmelanoma skin
  cancers is overexposure to the UV radiation in
  sunlight, which appears to disable a tumor
  suppressor gene
• However, frequent irritation of the skin by
  infections, chemicals, or physical trauma seems
  to be a predisposing factor

102
Skin Cancer

• Sunburned skin accelerates its production of Fas,
  a protein that causes genetically damaged skin
  cells to commit suicide, thus decreasing the risk
  of mutations that will cause sun-linked skin
  cancer
• It is the death of these gene-damaged cells that
  causes the skin to peel after a sunburn
• NEW lotions are being produced that will fix
  damaged DNA before the involved cells can develop
  into cancer cells
• These lotions contain tiny oily vesicles
  (liposomes) filled with enzymes that initiate
  repair of the DNA mutations most commonly caused
  by sunlight

103
Skin Cancer

• (a)Basal cell carcinoma is the least malignant
  and the most common skin cancer
• Stratum basale cells proliferate, invading the
  dermis and hypodermis
• Cancer lesions occur most often on sun-exposed
  areas of the face and appear as shiny,
  dome-shaped nodules that later develop a central
  ulcer with a pearly, beaded edge
• Relatively slow growing
• Metastasis seldom occurs before it is noticed
• Full cure by surgical excision is the rule in 99
  of cases

104
SKIN CANCER
105
Skin Cancer

• (b)Squamous cell carcinoma tends to grow rapidly
  and metastasize if not removed
• Arises from the keratinocytes of the stratum
  spinosum
• Lesion appears as a scaly reddened papule (small,
  rounded elevation) that arises most often on the
  head (scalp, ears, and lower lip), and hands
• If it is caught early and removed surgically or
  by radiation therapy, chance of complete cure is
  good

106
SKIN CANCER
107
Skin Cancer

• (c)Melanoma is the most dangerous of the skin
  cancers because it is highly metastatic and
  resistant to chemotherapy
• Cancer of the melanocytes
• Begin wherever there is pigment
• Most appear spontaneously
• About 1/3 develop from preexisting moles
• Usually appears as a spreading brown to black
  patch that metastasizes rapidly to surrounding
  lymph and blood vessels
• Key to surviving is early detection
• Chance of survival is poor if the lesion is over
  4mm thick
• Therapy is wide surgical excision accompanied by
  immunotherapy

108
SKIN CANCER
109
Skin Cancer

• American Cancer Society suggests you regularly
  examine your skin for new moles or pigmented
  spots and apply the ABCDE rule for recognizing
  melanoma
• A. Asymmetry
• The two sides of the pigmented spot or mole do
  not match
• B. Border irregularity
• The borders of the lesion exhibit indentations
• C. Color
• The pigmented spot contains several colors
  (blacks, browns, tans, and sometimes blues and
  reds)
• D. Diameter
• The spot is larger than 6 mm in diameter (the
  size of a pencil eraser)
• E. Elevation
• Elevation above the skin

110
Burns

• A burn is tissue damage inflicted by intense
  heat, electricity, radiation, or certain
  chemicals, all of which denature cell proteins
  and cause cell death to infected areas
• The most immediate threat to a burn patient is
  dehydration and electrolyte imbalance due to
  fluid loss
• Leads to renal shutdown and circulatory shock
  (inadequate blood circulation due to reduced
  blood volume)
• To save the patient, the lost fluids must be
  replaced immediately

111
Burns

• The volume of fluid lost can be estimated by
  computing the percentage of body surface burned
  (extent of the burns) using the rule of nines
  (ONLY APPROXIMATE)
• This method divides the body into 11 areas, each
  accounting for 9 of total body area, plus an
  additional area surrounding the genitals
  accounting for 1 of body surface

112
BURNS
113
Burns

• Burn patients also need thousands of extra food
  calories daily to replace lost proteins and allow
  tissue repair
• No one can eat this much, so burn patients are
  given supplementary nutrients through gastric
  tubes and intravenous (IV) lines
• After the first 24 hours has passed, the threat
  to a burn patient becomes infection to the wound
  site
• Burned skin is sterile for the first 24 hours
• Thereafter, bacteria, fungi, and other pathogens
  easily invade areas where the skin barrier is
  destroyed, and they multiply rapidly in the
  nutrient-rich environment of dead tissues
• Adding to this problem is the fact that the
  immune system becomes deficient one to two days
  after severe burn injury

114
Burns

• Burns are classified according to their severity
• First-degree burns involve damage only to the
  epidermis
• Tend to heal in two to three days without special
  attention
• Sunburn is usually a first-degree burn
• Second-degree burns injure the epidermis and the
  upper region of the dermis
• Blisters appear
• Skin regeneration occurs with little or no
  scarring within three to four weeks if care is
  taken to prevent infection
• Third-degree burns involve the entire thickness
  of the skin
• Burned area appears gray-white, cherry red, or
  blackened, and initially there is little or no
  edema (excessive tissue fluid-swelling)
• Since the nerve endings in the area have been
  destroyed, the burned area is not painful
• Skin grafting is usually necessary
• Excessive scar tissue usually forms

115
Burns

• Burns are considered critical if any of the
  following conditions exists
• 1. Over 25 of the body has second-degree burns
• 2. Over 10 of the body has third degree burns
• 3. There are third-degree burns of the face,
  hands, or feet
• Facial burns introduce the possibility of burned
  respiratory passageways, which can swell and
  cause suffocation
• Burns at joints are also troublesome because scar
  tissue formation can severely limit joint mobility

116
BURNS
117
ROSACEA
118
WINESTAIN
119
TATTO
120
DEVELOPMENTAL ASPECTSOF THEINTEGUMENTARY SYSTEM

• The epidermis develops from the embryonic
  ectoderm, and the dermis and the hypodermis
  develop from the mesoderm
• By the end of the fourth month of development the
  skin is fairly well formed
• During infancy and childhood, the skin thickens
  and more subcutaneous fat is deposited
• During adolescence, the skin and hair become
  oilier as sebaceous glands are activated
• The skin reaches its optimal appearance when we
  reach our 20s and 30s after that time the skin
  starts to show the effects of cumulative
  environmental exposures
• As old age approaches, the rate of epidermal cell
  replacement slows and the skin thins, becoming
  more prone to bruising and other types of
  injuries