WEEK 2: Tissues

• Tissues


  Basic structural and functional units of the body
• Basic tissue types


  • Muscular Tissue
  • Epithelial Tissue
  • Connective Tissue
  • Nervous Tissue
  • Skeletal Tissue, Cartilage and Bone
• Epithelial Tissue


  Aggregated polyhedral cells with small amount of extracellular matrix, main functions are lining of surface or body cavities and glandular secretion
• Connective Tissue


  Several types of fixed and wandering cells with abundant extracellular matrix, main functions are support and protection of tissues/organs
• Muscular Tissue


  Elongated contractile cells with moderate amount of extracellular matrix, main function is strong contraction and body movements
• Nervous Tissue


  Elongated cells with extremely fine processes and very small amount of extracellular matrix, main function is transmission of nerve impulses
• Epithelial Tissue


  • Covers external surfaces, lines internal cavities, forms organs and glands, lined by basement membrane, has junctional complexes

  
• Junctional Complexes


  • Zonulae occludentes (tight junctions)
  • Zonula adherens (assist in resisting separation)
  • Desmosomes (prevent separation of cells)
  • Hemidesmosomes (at base of epithelial cells)
  • Gap junctions (channels for communication)
• Classification of Epithelial Tissue

  • Simple (single layer)
  • Stratified (multiple layers)
  • Pseudostratified (single layer but not all cells reach surface)
  • Squamous (flat surface cells)
  • Cuboidal (round/as tall as wide surface cells)
  • Columnar (taller than wide surface cells)

  
• Epithelial Tissue


  • Nonvascular (no blood vessels)
• Cilia


  Motile structures on certain epithelial cells
• Microvilli


  Small, nonmotile projections on absorptive epithelial cells

  
• Stereocilia


  Long, nonmotile, branched microvilli on cells in epididymis and vas deferens

  
• Simple Squamous Epithelium


  • Mesothelium (covers digestive organs, lungs, heart)
  • Endothelium (covers heart chambers, blood/lymphatic vessels)

  
• Functions of Simple Squamous Epithelium

  Filtration, diffusion, transport, secretion, reduction of friction
• Simple Cuboidal Epithelium


  • Lines small excretory ducts, proximal convoluted tubules of kidney with brush border of microvilli

  
• Simple Columnar Epithelium


  • Covers digestive organs, stomach produces mucus, small intestine has absorptive cells with microvilli
• Pseudostratified Columnar Epithelium


  • Lines respiratory passages, epididymis and vas deferens (with stereocilia)
• Stratified Squamous Epithelium


  • Nonkeratinized (moist cavities) and Keratinized (external surfaces)

  
• Stratified Cuboidal and Columnar Epithelium

  • Line larger excretory ducts of pancreas, salivary glands, sweat glands
• Transitional Epithelium


  • Lines urinary system (changes shape when stretched or contracted)
• Exocrine Glands


  Have epithelial ducts carrying secretions, may be acinar, tubular or tubuloacinar
• Goblet Cells


  Unicellular exocrine glands that secrete mucin
• Types of Exocrine Glands

  • Mucous Glands
  • Serous Glands
• Endocrine Glands


  Lack ducts, secrete hormones into interstitial fluid and blood
• Connective Tissue


  Develops from mesenchyme, binds, anchors and supports cells, tissues and organs
• Types of Connective Tissue

  • Loose Connective Tissue
  • Dense Connective Tissue
• Loose Connective Tissue


  • Irregular arrangement of fibers, abundant ground substance, collagen fibers, fibroblasts, adipose cells, mast cells, macrophages
• Dense Connective Tissue


  • Thicker and more densely packed collagen fibers, fewer cell types, less ground substance, found in dermis, organ capsules, areas needing strong support
• Types of Dense Connective Tissue

  • Dense Irregular
  • Dense Regular
• Fibroblasts


  Most abundant cells in connective tissue, synthesize fibers and ground substance
• Fibrocytes


  Inactive or resting fibroblasts
• Macrophages/Histiocytes


  Phagocytic cells in connective tissue
• Adipose Cells


  Store fat in connective tissue
• Mast Cells


  Associated with blood vessels, contain granules, found in skin, digestive and respiratory organs
• Plasma Cells


  Derived from lymphocytes, found in connective tissue of respiratory and digestive tracts
• Leukocytes


  White blood cells (neutrophils, eosinophils) that migrate into connective tissue to defend against infection
• Connective Tissue Fibers


  • Collagen Fibers
  • Reticular Fibers
  • Elastic Fibers
• Collagen Fibers


  Tough, thick, fibrous proteins (Types I, II, III, IV) that provide tensile strength and resistance to pressure
• Reticular Fibers


  Thin, branching fibers of Type III collagen that form delicate supporting meshworks