Integumentary System

• Functions of the skin

  • Protection
  • Sensation
  • Thermoregulation
  • Metabolism
  • Sexual signaling
• Epidermal ridges


  Peg and socket interdigitations in skin that form distinctive patterns unique for each individual (dermatoglyphs)
• Adermatoglyphia


  Absence of fingerprints, a rare genetic condition discovered by Prof. Peter Itin in 2007
• Epidermis


  Keratinized stratified squamous epithelium
• Cells in the epidermis

  • Melanocytes
  • Keratinocytes
  • Langerhans cells
  • Merkel cells
• Layers of the epidermis

  • Stratum basale
  • Stratum spinosum
  • Stratum granulosum
  • Stratum lucidum (thick skin)
  • Stratum corneum
• Melanin formation


  Melanosomes within melanocytes convert tyrosine to melanin (pheomelanin or eumelanin) which forms a cap-like structure to protect keratinocytes from UV
• Basement membrane


  Found between the basal layer of the epidermis and the papillary layer of the dermis
• Papillary layer of dermis


  Loose connective tissue with dermal papillae (conical projections)
• Reticular layer of dermis


  Dense irregular connective tissue providing skin toughness and strength, containing elastic fibers, mast cells and macrophages
• Subcutaneous layer (hypodermis)


  Loose connective tissue (adipose) with extensive vascular supply
• Unencapsulated sensory receptors


  • Tactile disk (Merkel's disks)
  • Free nerve endings
  • Root hair plexuses (hair follicle receptor)
• Encapsulated sensory receptors


  • Tactile corpuscles (Meissner's corpuscles)
  • Pacinian corpuscles (Vater-pacinian)
  • Krause and Ruffini corpuscles
• Hair


  Elongated keratinized structures that form within epidermal invaginations, with a cuticle, cortex, and medulla
• Hair bulb


  Contains the matrix which contains keratinocytes and melanocytes
• Arrector pili


  Smooth muscle that contracts to pull the hair follicle nearly perpendicular, increasing space among hairs to improve insulation (goose flesh)
• Stages of the hair cycle

  • Anagen (active growth)
  • Catagen (stops growing, detaching slowly)
  • Telogen (follicle rest, prepares next cycle)
• Nails


  Hard plates of keratin on the dorsal surface of each distal phalanx, with a lunula, matrix, and nail body
• Types of skin glands

  • Sebaceous
  • Apocrine
  • Merocrine/Eccrine
• Sebaceous glands


  Secrete sebum into hair follicles, with simple branched acinar structure and holocrine secretion
• Apocrine glands


  Sweat glands near hair, in axillary and perianal regions, with cloudy (mucous) secretion that may contain pheromones
• Merocrine/Eccrine glands


  Widely distributed, clear watery (serous) secretion for thermoregulation