Integumentary system

• The Skin

  • The largest organ in the body
  • Surface area 1.5-2 m2
  • Two main layers: epidermis, dermis
  • Accessory structures: glands, hair and nails
• Epidermis

  • Stratified keratinised squamous epithelium
  • Variable thickness - thickest on palms and soles
  • No blood vessels or nerve endings
  • Superficial layer is stratum corneum (thick horny layer)
  • Deepest layer is germinative layer (where epidermal cells originate)

  
• Stratum corneum


  Keratinized cells (dead), progressively removed
• Dermis

  • Tough and elastic
  • Contains elastic and collagen fibers
  • Contains fibroblasts, macrophages, mast cells
  • Contains blood and lymph vessels
  • Contains sensory nerve endings
• Fibroblasts


  Synthesize the extracellular matrix and collagen, play a critical role in wound healing
• Macrophages


  Cells of the immune system that engulf and digest cellular debris, foreign substances, microbes, cancer cells
• Sensory (cutaneous) receptors in the dermis


  • Meissner's corpuscle (light pressure)
  • Pacinian corpuscle (deep pressure)
  • Free nerve endings (pain)

  
• Sebaceous gland


  Exocrine gland that secretes sebum to lubricate hair and skin
• Hair


  • Hair papilla (cluster of cells at base that multiply)
  • Shaft (part above skin)
  • Root (part under skin)
• Arrector pili muscle


  Small bundles of smooth muscle fibres attached to hair follicles that contract to make hair erect
• Sweat glands


  • More numerous in palms, soles, axillae and groins
  • Eccrine vs. apocrine
• Exocrine glands


  Have ducts to carry secretion to site of function
• Endocrine glands

  Ductless, secrete hormones that enter bloodstream
• Pacinian corpuscles

  Respond to mechanical stimuli such as pressure, located deep in skin, joints, ligaments and tendons
• Nails

  • Root embedded in skin, covered by cuticle
  • Nail bed is germinative zone
  • Lunula is hemispherical pale area
  • Nail plate is exposed part grown from nail bed
  • Nail body is visible portion
• Finger nails


  Grow faster than toe nails
• Functions of the skin


  • Protection (from microorganisms, chemicals, physical agents)
  • Regulation of body temperature
  • Formation of vitamin D
  • Cutaneous sensation
  • Absorption
  • Excretion
• Wound healing 


  1. Inflammation and migratory phase

  2. Proliferation

  3. Maturation
• Granulation tissue(wound healing process)


  Transient, specialized tissue of repair with fibroblasts, phagocytes and new capillary buds
• Pressure ulcers

  Skin compressed between bones and hard surface, leading to ischemia and necrosis
• Pus


  Exudate formed at site of inflammation during bacterial or fungal infection, containing phagocytes, dead cells, cell debris, microbes
• Skin abscess

  Pocket of pus, similar to a pimple but larger and deeper under skin
• Superficial abscess can heal by early rupture and release of pus, or removal of pus by phagocytes
• Deep abscess can develop into a chronic abscess with an infected channel (sinus)
• Site of inflammation during bacterial or fungal infection


  • Contains phagocytes, dead cells cell debris, inflammatory exudate
  • Contains living and dead microbes e.g. Staphylococcus aureus or Staphylococcus pyogenes
• Types of skin abscess


  • Superficial abscess
  • Deep abscess
• Skin aging


  • Germinative layer becomes less active à epidermis thins
  • Fewer elastic and collagen fibres à the dermis thins
  • Chronic exposure to sun UV light contributes
  • Sweat gland activity and temperature regulation is less efficient à risk of heatstroke or hypothermia is larger
  • Melanocytes produce less melanin, cells are not well protected
  • Fewer hair follicles, so hair thins
• 1st degree burn


  • Only epidermis is involved
  • Inflammation, redness, swelling and pain
• 2nd degree burn


  • Epidermis and upper dermis involved
  • Blisters (additionally to the above)
• 3rd degree burn


  • Epidermis and dermis are destroyed / deep and full thickness
  • Usually painless as nerve ending are destroyed
  • After a few days the destroyed cell coagulate forming an eschar (thick scab), which is removed after 2-3 weeks
  • In circumferential burns, which encircle body areas, complications may arise e.g. respiratory problems in the chest
  • Skin grafting is required sometimes
• Seriousness of burns

  • Depth & extend of area involved
  • Age of person
  • General health
• Secondary systemic effects of burns


  • Loss of water, plasma, plasma proteins causes dehydration and hypovolaemia à shock
  • Hypothermia
  • Bacterial infection
  • Reduced circulation of blood
  • Decrease in urine production
  • Compromised immune response
• Major burns


  • 10% area of 3rd degree burns
  • 25% area of 2nd degree burns
  • Face, hands, feet, perineum (anal and urogenital regions)
• Fatality from burns
• Psoriasis


  • Condition genetically determined
  • Proliferating cells from basal layers progress more rapidly upwards through the epidermis à incomplete maturation of the upper layer
  • Skin cells are normally made and replaced every 3 to 4 weeks, but in psoriasis this process only takes about 3 to 7 days
  • Red, scaly plaques with a silver surface
  • Bleeding may occur when plaques get rubbed off
  • Common in elbows, knees and scalp
  • Worsening in trauma, infection or sun burn
• Dermatitis / Eczema


  • Inflammatory skin condition
  • Acute: redness, swelling, exudation of serous fluid and itching, crusting and scaling
  • Chronic: skin thickens, may become leathery (from long term scratching), get infected
  • Atopic dermatitis: associated with allergy & affects individuals with hypersensitivity disorders e.g. children with hay fever or asthma
  • Contact dermatitis: through direct contact with irritants e.g. cosmetics, soap, detergent, alkalis, acids, latex metals (nickel), perfums, days etc.
• Acne vulgaris


  • Mostly driven by testosterone during puberty and adolescence
  • Sebaceous glands (in hair follicles) become blocked and infected à inflammation, pustule formation, rarely scarring
  • Face, chest, upper back
• Ringworm


  • Contagious fungal infection caused by common mold-like parasites
  • Outward spreading ring red/silver rash risg-shaped or inflammation via skin-to-skin contact
  • Commonly affects the scalp, feet and groin and can spread to others
• Tinea pedis (athlete's foot)


  • Affects the skin between the toes
  • Spread by direct contact
  • Wash of socks, towels etc. over 60oC
• Basal cell carcinoma


  • The most common skin cancer type
  • Least malignant/dangerous
  • Associated with long-term exposure to sunlight
  • Starts as a shiny nodule that becomes an ulcer
  • Locally invasive, rarely metastatic