The Integumentary System P1

• Integumentary system


  Largest system of the body, approx. 16% of total body weight, 1.5 to 2 m2 of surface area, contains blood vessels and sensory receptors
• Major parts of the integument

  • Cutaneous membrane (skin)
  • Accessory structures

  
• Cutaneous membrane


  • Contains epidermis (outer, superficial epithelium)
  • Contains dermis (inner, connective tissues)

  
• Accessory structures


  • Originate in the dermis
  • Extend through the epidermis to skin surface
  • Include hair and hair follicles, exocrine glands, nails

  
• Hypodermis


  Loose connective tissue below the dermis
• Functions of the integument

  • Protection of underlying tissues and organs
  • Excretion of salts, water, and organic wastes
  • Maintenance of normal body temperature
  • Production of melanin
  • Production of keratin
  • Synthesis of vitamin D3
  • Storage of lipids
  • Detection of touch, pressure, pain, etc.
  • Coordination of the immune response
• Epidermis


  • Comprised of stratified squamous epithelium
  • Avascular, nutrients and oxygen diffuse from capillaries in the dermis
• Keratinocytes


  The body's most abundant epithelial cells, contain large amounts of keratin
• Thin skin


  • Covers most of the body
  • Has four layers of keratinocytes

  
• Thick skin


  • Covers the palms of the hands and soles of the feet
  • Has five layers of keratinocytes

  
• Layers of epidermis in thick skin

  • Stratum basale
  • Stratum spinosum
  • Stratum granulosum
  • Stratum lucidum
  • Stratum corneum

  
• Stratum basale


  Deepest, basal layer, attached to basement membrane, contains basal cells (stem cells), melanocytes, and tactile cells (Merkel cells)
• Stratum spinosum


  • Eight to ten layers of keratinocytes bound by desmosomes, cells appear spiny, contains dendritic (Langerhans) cells active in immune response
• Stratum granulosum


  • Three to five layers of keratinocytes, produces keratin and keratohyalin which promotes cellular dehydration and cross-linking of keratin fibers
• Stratum lucidum


  Found only in thick skin, covers stratum granulosum
• Stratum corneum


  • Exposed surface of skin, 15 to 30 layers of keratinized cells, water resistant, new cells move from stratum basale in 7 to 10 days, exposed cells shed after two weeks
• Insensible perspiration


  Water diffuses across stratum corneum and evaporates from skin, 500 mL per day, rate increases if stratum corneum is damaged
• Sensible perspiration


  Water excreted by sweat glands
• Epidermal growth factor (EGF)


  A peptide growth factor produced by salivary glands and duodenum, used in laboratories to grow skin grafts, promotes division of basal cells, accelerates keratin production, stimulates epidermal repair and glandular secretion
• Stratum corneum


  • Found only in thick skin
  • Covers stratum granulosum
• Stratum corneum


  The "horny layer"
• Stratum corneum


  • Exposed surface of skin
  • Water resistant
  • 15 to 30 layers of keratinized cells
• Keratinization


  The formation of protective layers of cells filled with keratin
• Cell movement in stratum corneum

  1. New cells move from stratum basale to stratum corneum in 7 to 10 days

  2. Exposed cells are shed after two weeks
• Insensible perspiration


  • Water diffuses across stratum corneum and evaporates from skin
  • 500 mL per day
  • Rate increases if stratum corneum is damaged (e.g., from burns)
• Epidermal growth factor (EGF)


  • A peptide growth factor
  • Produced by salivary glands and duodenum
  • Used in laboratories to grow skin grafts
• Functions of EGF


  • Promotes division of basal cells
  • Accelerates keratin production
  • Stimulates epidermal repair
  • Stimulates glandular secretion
• Dermis


  • Located between epidermis and subcutaneous layer
  • Anchors epidermal accessory structures (e.g., hair follicles and sweat glands)

  
• Components of dermis


  • Outer papillary layer
  • Deeper reticular layer

  
• Papillary layer


  • Consists of areolar tissue
  • Contains capillaries, lymphatic vessels, and sensory neurons
  • Named for dermal papillae that project between epidermal ridges
  • Becomes inflamed in "dermatitis"
• Reticular layer


  • Consists of dense irregular connective tissue
  • Contains collagen and elastic fibers
  • Contains all cells of connective tissue proper

  
• Collagen fibers


  • Very strong, resist stretching
  • Easily bent or twisted
  • Limit flexibility to prevent tissue damage
• Elastic fibers


  • Permit stretching and then recoil to original length
  • Provide flexibility
• Skin turgor


  Flexibility and resilience provided by fibers and water
• Loss of skin turgor is caused by

  • Dehydration (reversible)
  • Aging
  • Hormones
  • UV radiation
• Excessive distortion of skin

  May cause stretch marks
• Tension lines (cleavage lines)


  • Parallel bundles of collagen and elastic fibers in the dermis
  • Resist forces applied to skin
  • A cut made parallel to a tension line remains shut, heals well
  • A cut at a right angle pulls open and scars
• Cutaneous plexus


  Deep network of arteries along the reticular layer
• Subpapillary plexus


  • Network of small arteries in papillary layer
  • Capillaries drain into small veins that lead to larger veins in subcutaneous layer
• Contusion (bruise)


  Caused by damage to blood vessels in dermis