Integumentary system

• Epithelial tissues


  Composed of closely aggregated polyhedral cells that adhere to one another and to the thin layer of extracellular matrix (ECM)
• Epithelial tissues


  Form a cellular sheet that lines the cavities of the organs
• Epithelium


  Tissue in which cells are bound tightly together
• Epithelium


  Form a sheetlike or tubular structure with little extracellular material between the cells
• Parts of epithelial cells

  • Apical side: facing the sheet's free surface
  • Basal side: facing a basement membrane and underlying connective tissue
• Absorption or transcytosis in epithelial cells

  1. Pinocytosis of material at the apical side

  2. Exocytosis at the basolateral side
• Epithelial tissues exhibit continuous renewal
• The location of stem cells and the rate of cell turnover in epithelial tissues is variable depending on the type of epithelium
• Basement membrane


  A thin extracellular layer of specialized proteins, ECM
• Parts of the basement membrane

  • Basal lamina
  • Reticular lamina
• Basal lamina


  A thin meshwork of type IV collagen and laminin produced by epithelial cells
• Reticular lamina


  Contains type III collagen and anchoring fibrils of VII collagen
• Tight or occluding junctions


  Formed by interacting transmembrane proteins, such as claudin and occludin
• Tight or occluding junctions


  Linear arrangements around the apical end of the cells and prevent paracellular passage of substances
• Adherent or anchoring junctions


  Formed by interacting proteins of the cadherin family
• Adherent junctions


  Form zonula adherens that encircle epithelial cells
• Adherent junctions


  Spot-like attachment sites called desmosomes or maculae adherens
• Adherent junctions


  Both of which are attached to the cytoplasmic keratins
• Skin/Integument/Cutaneous layer


  Largest single organ of the body
• Skin/Integument/Cutaneous layer


  Typically accounting for 15% to 20% of total body weight and, in adults, presenting 1.5 to 2 m2 surface to the external environment
• Functions of the skin

  • Protection: Provides a physical barrier against thermal and mechanical insults, such as friction, and against most potential pathogens and other material
  • Sensory: Allows skin to constantly monitor the environment, and various skin mechanoreceptors help regulate the body's interactions with physical objects
  • Thermoregulatory: Maintains a constant body temperature, thanks to the skin's insulating components and mechanisms for accelerating heat loss
  • Metabolic: Cells of skin synthesize vitamin D3
  • Sexual Signaling: Many features of skin, such as pigmentation and hair, are visual indicators of health involved in attraction between the sexes
• Thick skin


  Covers palms and soles, 400 to 1400 um (1.44 mm) thick, highly keratinized
• Thin skin


  Covers the whole body except the palms and the soles, varies from 75 to 150 um thick
• General layers of the skin

  • Epidermis
  • Dermis
  • Hypodermis
• Epidermis


  Superficial layer
• Dermis


  Underlying connective tissue and its under epidermis
• Hypodermis


  Subcutaneous layer composed of loose connective tissue
• Cells in the epidermis

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


  Most abundant cells of the epidermis, responsible for producing keratin
• Melanocytes


  They produce melanin, the pigment responsible for skin color, which protects the skin from UV radiation
• Langerhans cells


  Part of the immune system, protect the skin from pathogens by identifying and presenting antigens to other immune cells
• Merkel cells


  Found in the deepest layer of the epidermis, involved with the sensation of touch
• Layers of the epidermis

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


  Also called stratum germinativum, attached to basement membrane by hemidesmosome, forms epidermal ridges down into dermis, contains basal or germinative cells
• Stratum spinosum


  The result of stem cell division, flat but irregularly shaped
• Stratum granulosum


  Cells make a lot of keratin, a protein that provides water resistance and the foundation for hair and nails, contains granules filled with proteins and lipids important for skin barrier
• Stratum lucidum


  Cells are densely packed into a highly keratinized layer, only found in thick skin (palms and soles)
• Layers of the dermis

  • Papillary layer
  • Reticular layer
• Papillary layer


  Upper layer of the dermis, directly beneath the epidermis, composed of loose connective tissue, contains papillae (small finger-like projections that extend to the epidermis and contain capillaries that supply nutrients and oxygen to the epidermis)
• Reticular layer


  Deeper layer of dermis, composed of dense irregular connective tissue which provides strength and elasticity to the skin