Chapter 5 integumentary system

• Integumentary system


  Includes the skin and accessory structures such as hair, nails, and glands
• Major functions of the integumentary system


  • Protection
  • Sensation
  • Temperature regulation
  • Vitamin D production
  • Excretion
• Protection


  • Reduces negative and harmful effects of ultraviolet light
  • Keeps microorganisms from entering the body
  • Prevents dehydration by reducing water loss
• Epidermis


  Superficial layer of the skin, consisting of stratified squamous epithelium
• Dermis


  Layer of connective tissue responsible for most of the strength of the skin
• Subcutaneous tissue


  Layer of loose connective tissue that connects the skin to underlying muscles or bones
• Layers of the epidermis


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


  Most superficial stratum of the epidermis, composed of 25 or more layers of dead squamous cells
• Stratum lucidum


  Three to five layers of dead, flattened cells that appear transparent; present in thick skin, absent in most thin skin
• Stratum granulosum


  1. 10 layers of many-sided cells that produce keratohyalin granules and lamellar bodies
• Stratum spinosum


  Many-sided cells that produce keratin fibers and lamellar bodies
• Stratum basale


  Deepest stratum of the epidermis, single layer of cuboidal or columnar cells that produce new cells
• Keratinization


  Continuous process as cells change and move from the deeper layers to the surface
• The number of layers and strata in the skin varies depending on the location in the body
• Cells in the epidermis


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


  Cells that produce the protein keratin, making the cells more durable
• Melanocytes


  Cells that produce the pigment melanin, which contributes to skin color
• Langerhans cells


  Part of the immune system
• Merkel cells


  Specialized sensory cells associated with nerve endings responsible for detecting light touch
• The epidermis does not contain blood vessels, it receives nutrients and removes waste products through the exchange between the epidermis and the capillaries in the dermis
• The epidermis is separated from the dermis by a basement membrane
• The dermis is responsible for the structural strength and flexibility of the skin
• Layers of the dermis


  • Papillary layer
  • Reticular layer
• Papillary layer


  Loose connective tissue with papillae that project toward the epidermis
• Reticular layer


  Mat of collagen and elastic fibers, dense irregular connective tissue
• The subcutaneous tissue is not part of the skin or the integumentary system, but it connects the skin to underlying muscles or bones
• The subcutaneous tissue contains adipose tissue that provides energy storage, insulation, and padding
• The subcutaneous tissue also contains blood vessels and nerves that supply the dermis
• Epidermis


  Divided into regions or strata
• Epidermal strata


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


  • Single layer of cuboidal or columnar cells
  • Anchored to basement membrane by hemidesmosomes
  • Keratinocytes strengthened internally by keratin
• Keratinocyte stem cells


  Undergo mitotic divisions approximately every 19 days
• Stratum spinosum


  • 8-30 layers of many-sided cells
  • Cells flatten as pushed to surface
  • Desmosomes break apart and new ones form
  • Additional keratin fibres and lipid-filled organelles called lamellar bodies form
• Stratum granulosum


  • 2-5 layers of somewhat flattened, diamond-shaped cells
  • Presence of protein granules of keratohyalin
  • Lamellar bodies release contents into extracellular space
  • Protein envelope forms beneath plasma membrane
  • Organelles degenerate, keratinocyte dies
• Stratum lucidum


  • Thin, clear layer above stratum granulosum
  • Consists of several layers of dead keratinocytes with indistinct boundaries
  • Keratin fibres present but keratolyasin has dispersed
• Stratum corneum


  • 25 or more layers of dead, overlapping squamous cells
  • Cells joined by desmosomes which eventually break apart
  • Consists of cornified cells filled with protein keratin
• Lipids are released from lamellar bodies between skin cells and are responsible for many of the skin's permeability characteristics
• Thick skin


  Has all 5 epidermal strata, stratum corneum has many cell layers, found in areas subject to pressure/friction
• Thin skin


  Covers rest of body, more flexible, stratum lucidum generally absent, fewer cell layers in each stratum
• Variation in skin thickness is mainly due to differences in dermis thickness, not epidermis