Integumentary

• Skin


  • Largest single organ of the body
  • 15%-20% of total body weight
• Layers of the skin

  • Epidermis
  • Dermis
  • Hypodermis

  
• Functions of the skin

  • Protection
  • Sensory
  • Thermoregulatory
  • Metabolic
  • Sexual Signaling
• Mechanoreceptors


  Receptors for touch
• Insulating components of the skin

  Fatty layer
• Epidermis


  • Stratified Keratinized Squamous Epithelium
  • Lacks vasculature
  • Receives nutrients only from the dermis
• Primary cells in the epidermis

  • Keratinocytes
  • Melanocytes
  • Langerhans cells
  • Merkel Cells
• Epidermis forms distinction between THICK and THIN Skin

  
• Thick skin


  Palms and Soles (400 – 1400 um )
• Thin skin


  Everywhere Else (75 – 150 um)
• Keratinocytes


  Produce keratin and are responsible for the solidification of our skin
• Layers of the epidermis

  • Stratum Corneum
  • Stratum Lucidum
  • Stratum Granulosum
  • Stratum Spinosum
  • Stratum Basale
• Stratum Corneum


  20-30 layers of dead, flattened, anucleate, keratin-filled keratinocytes called squames which are bound by hydrophobic, lipid-rich intercellular cement
• Stratum Lucidum


  1. 3 layers of anucleate, dead cells; seen only in thick skin
• Stratum Granulosum


  • 3-5 layers of keratinocytes with distinct kerato-hyaline granules which are intensely basophillic
  • Contains lamellar granules (Golgi-derived) structures with many lamellae containing various lipids and glycolipids
  • Produces a lipid-rich, impermeable layer around the cells forming a major part of the skin's barrier against water loss
• Stratum Spinosum


  • Thickest layer
  • Polyhedral cells with central nuclei
  • Several layers of keratinocytes all joined by desmosomes
  • Contains tonofibrils (keratin filament bundles)
  • Cells may still divide (germinativum)
• Stratum Basale


  • Single layer of cuboidal to low columnar cells in contact with basement membrane
  • Mitosis occurs here
  • Melanocytes and Merkel cells also present
• Melanocytes


  • Located at basal epidermis
  • Neural Crest Derived
  • Synthesize dark melanin pigment in melanosomes
  • Protect nuclear DNA from UV damage
• Eumelanin


  Brown or black pigment; found in hair follicles
• Pheomelanin


  Red hair
• Langerhans Cells


  • Antigen Presenting Cells (APC)
  • 2-8% of cells in epidermis
  • Located at spinous layer of epidermis
  • Bind, process and present antigens to T-lymphocytes
• Merkel Cells


  • Epithelial Tactile Cells
  • Mechanoreceptors for light touch
  • Abundant in fingertips and bases of some hair follicles
  • Characterized by small, Golgi-derived dense-core neurosecretory granules containing peptides
• Dermis


  • Layer of connective tissue
  • Supports epidermis and binds it to hypodermis
  • Contains projections called dermal papillae; connects with epidermal ridges
  • Filled with nerves (Sensory Efferent Fibers)
• Basement Membrane


  Connects dermis with epidermis
• Layers of the dermis

  • Papillary Layer
  • Reticular Layer

  
• Papillary Layer


  • Connects to epidermis
  • Contains loose connective tissue, type I and III collagen, mast cells, dendritic cells, fibrils of type VII collagen

  
• Reticular Layer


  • Thicker than papillary layer
  • Contains dense connective tissue, fewer cells than papillary layer, elastic fibers
• Between the papillary and reticular dermal layers lies the microvascular subpapillary plexus containing capillary branches that extend to dermal papillae

  
• A deep plexus with larger blood and lymphatic vessels lies near the interface of the dermis and the subcutaneous layer
• Thermoregulatory function of the dermis

  Arteriovenous anastomoses located between both plexuses decrease blood flow in the papillary layer to minimize heat loss in cold conditions and increase this flow to facilitate heat loss when it is hot, thus helping maintain a constant body temperature
• Dermis


  The layer of skin between the epidermis and the subcutaneous layer

  
• Reticular Layer


  • Thicker than Papillary Layer
  • Contains dense connective tissue
  • Contains fewer cells than papillary layer
  • Contains elastic fibers
• Papillary Layer


  The layer of the dermis closest to the epidermis

  
• Microvascular subpapillary plexus


  Contains capillary branches that extend to dermal papillae
• Deep plexus


  Contains larger blood and lymphatic vessels near the interface of the dermis and the subcutaneous layer
• Arteriovenous anastomoses


  Located between both plexuses, responsible for the thermoregulatory function of the dermis
• Thermoregulatory function


  The shunts decrease blood flow in the papillary layer to minimize heat loss in cold conditions and increase this flow to facilitate heat loss when it is hot, thus helping maintain a constant body temperature
• Subcutaneous layer


  Also known as Hypodermis or Superficial Fascia, contains adipocytes
• Sensory receptors


  • Uncapsulated
  • Capsulated
• Uncapsulated receptors


  • Simple nerve endings with no Schwann cell or collagenous coverings