Integumentary System

• Integumentary system


  Also known as the skin or cutaneous layer

  
• Integumentary system


  • Composed of skin, hair, nails, sweat and sebaceous glands, sensory receptors
• Functions of skin


  • Protective function
  • Sensory function
  • Secretory function
  • Heat regulatory function
  • Excretory function
  • Synthetic function
  • Water balance
• Protective function of skin

  • Protects our body from infection, pathogens, and harmful UV irradiation
• Sensory function of skin

  • Free nerve endings on the skin are sensitive to pain, touch, heat and cold, resulting in either voluntary or reflex activities
• Secretory function of skin

  • Sweat helps in temperature regulation and sebum makes skin smooth
• Heat regulatory function of skin

  • Sweating and cutaneous blood flow help in temperature regulation
• Excretory function of skin

  • Water, salt, fatty substances and urea are excreted through the secretion of glands of the skin
• Synthetic function of skin

  • Sun's ultraviolet rays help in synthesis of natural vitamin D, skin can also manufacture melanin pigment
• Water balance function of skin

  • Skin serves a useful means in regulating water balance of the body by perspiration
• Integumentary system


  • Largest organ in the body, 16% body weight, 1.5-2 ㎡ in area
• Main layers of integumentary system

  • Epidermis
  • Dermis
  • Subcutaneous layer
• Epidermis


  Superficial epithelium, ectodermal origin
• Dermis


  Underlying connective tissue with blood supply, mesodermal origin, dense irregular connective tissue
• Subcutaneous layer


  Loose connective tissue layer usually containing pads of adipocytes
• Composition of lipid membrane


  The most important barrier lipids are ceramides, cholesterol and free fatty acids. Quantitative and qualitative changes in the composition of these lipids can lead to a disturbed barrier function.
• Protective functions of skin

  • Prevents dehydration
  • Prevents infection
  • Physical barrier to injury
  • Protects against ultraviolet light injury (Melanin)
• Thermoregulation functions of skin


  • Insulation (hair and adipose tissue)
  • Heat dissipation through sweat evaporation and increased blood flow
• Metabolic functions of skin

  • Energy storage of Triglycerides in adipose tissue
  • Vitamin D synthesis
• Epidermis


  Stratified squamous keratinized epithelium, avascular, 90% of epidermal cells are keratinocytes that produce keratin
• Cells of the epidermis

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

  • Stratum germinativum
  • Stratum spinosum
  • Stratum granulosum
  • Stratum lucidum
  • Stratum corneum

  
• Stratum germinativum


  Provides the germinal cells necessary for the regeneration of the layers of the epidermis, separated from the dermis by a thin layer of basement membrane
• Stratum spinosum


  The cells that divide in the stratum germinativum soon begin to accumulate many desmosomes on their outer surface which provide the characteristic prickles
• Stratum granulosum


  The cells accumulate dense basophilic keratohyalin granules which contain lipids, helping to form a waterproof barrier

  
• Stratum lucidum


  Represents a transition from the stratum granulosum to the stratum corneum, no nucleus in this layer
• Stratum corneum


  The outermost layer of the epidermis, consisting of dead cells (corneocytes) that lack nuclei and organelles, desquamation balances proliferating keratinocytes
• Types of skin


  • Thin skin
  • Thick skin
• Thi skin

  • 5 layers, prominent stratum corneum, well developed stratum granulosum, found on palms of hands and soles of feet, thinner dermis, no hair and sebaceous glands

  
• Thi skin

  • 4 layers, less prominent stratum corneum, less developed stratum granulosum, dominant and lines most of the body surface, thicker dermis, hair and sebaceous glands
• Types of epidermal cells

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


  Formed of many layers that continuously shed and regenerate every 2-4 weeks, responsible for keratin formation, arranged in many layers, form melanin
• Melanocytes


  Found in between cells of the basal layer, branched cells with central nuclei containing organelles for protein synthesis
• Langerhans cells


  Dendritic (antigen-presenting immune) cells found in upper layers of stratum spinosum, have branched shape and central nuclei
• Merkel cells


  Found in basal cell layer, function as touch and pressure receptors, modified epidermal cells with sensory nerve fibers forming terminal disks under them
• Dermis


  Supports the epidermis and binds it in the subcutaneous tissue, supplies the avascular epidermis with nutrients, typically subdivided into papillary dermis and reticular layer
• Papillary dermis


  Loose areolar connective tissue containing vascular networks to support the avascular epidermis and provide thermoregulation
• Reticular dermis


  Consists of mainly dense irregular connective tissue, important in giving the skin overall strength and elasticity, houses epithelial derived structures like glands and hair follicles
• Components of the dermis

  • Fibroblasts
  • Mast cells
  • Adipocytes
• Fibroblasts


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