Epithelial and connective tissue

• Tissue


  A group of cells with a common embryonic origin that function together to carry out specialized activities
• Histology


  The science that deals with the study of tissues
• Pathologists


  Specialise in laboratory studies of cells and tissues for diagnoses
• Four basic tissue types

  • Epithelial
  • Connective
  • Muscular
  • Nervous
• Epithelial tissue


  • Covers body surfaces and lines hollow organs, body cavities, duct, and forms glands
• Connective tissue


  • Protects, supports, and binds organs
  • Stores energy as fat
  • Provides immunity
• Cell junctions


  • Contact points between membranes of tissue cells
  • Five main types: tight junctions, adherens, desomosomes, hemidesmosomes and gap junctions
• Tight junctions


  Web-like strands of transmembrane proteins that fuse together at outer surfaces of cells to seal passageways between cells
• Adherens junctions


  • Contain plaque protein which anchors membrane proteins to cytoskeleton
  • Cadherins - transmembrane glycoproteins join adjacent cells
• Desmosomes and Hemidesmosomes


  • Like adherens, contain plaque protein and Cadherins
  • Plaque attaches to intermediate filaments in cells (Keratin)
  • Intermediate span cells providing stability
  • Contain Integrin transmembrane glycoproteins which attach to intermediate filaments inside cell and anchor to basement membrane
• Cytoskeleton


  • Network of protein filaments throughout the cytosol
  • Provides structural support for the cell
  • Three types: Actin/Myosin, Tubulin, Hollow tubes
• Gap junctions


  • Cells connected by connexons - fluid filled transmembrane holes made from connexins
  • Allows diffusion of ions/small molecules
  • Provides electrical coupling between cells
• Epithelial tissue has no blood vessels
• Epithelia form surface layers and are not covered (except lining blood vessels)
• Surfaces of epithelial cells and basement membrane


  • Apical surfaces may contain cilia or microvilli
  • Lateral surfaces may contain junctions
  • Basal surface binds the basement membrane
• Basement membrane


  Consists of two extracellular layers: 1) Basal lamina contains laminin and collagen, 2) Reticular lamina contains fibroblasts which secrete collagen
• Classification of epithelial tissues by shape

  • Squamous = flat
  • Cuboidal = cube-shaped
  • Columnar = tall column
  • Transitional = shape varies with tissue stretching
• Classification of epithelial tissues by arrangement

  • One layer - all cells in contact with basement membrane
  • Two or more layers - only basal layer in contact with basement membrane
• Simple squamous epithelium


  • Lining surfaces involved in passive transport (diffusion); Gases (lungs), Liquids (walls of blood capillaries called endothelium), Epithelial layer of serous membranes or serosa (mesothelium)
• Simple cuboidal epithelium


  • Functions in secretion and absorption
  • Usually lines small ducts and tubules
  • Covers surface of ovary
  • Lines kidney, salivary and pancreatic tubules
• Non-ciliated simple columnar epithelium

  • Exhibit elongated nuclei
  • Found on highly absorptive surfaces, i.e. lining gastrointestinal tract
  • Microvilli increase surface area for absorption
  • Goblet cells - secrete mucus
• Ciliated simple columnar epithelium


  • Cilia are much larger than microvilli, up to 300 per cell
  • Cilia beat to propel fluid or material over the epithelial surface
  • Not common, lines fallopian tubes in female reproductive system
• Pseudostratified columnar epithelium


  • Appears to have several layers (stratified) but all cells contact basement membrane
  • Nuclei all at different levels (not columnar)
  • Ciliated variety almost exclusive to lining upper respiratory tract
• Stratified squamous epithelium


  • Keritanised variety forms superficial layer of skin (epidermis)
  • Non-keritanised variety lines wet surfaces (mouth, oesophagus and vagina)
  • Protects against abrasion, water loss, UV, defence against microbes
• Stratified cuboidal epithelium


  • Thin, usually only 2-3 cells thick
  • Found in ducts of sweat glands
  • Provide protection to other tissues
• Transitional epithelium


  • Variable appearance
  • Almost exclusively lines urinary system - bladder, ureters and urethra
  • Allows urinary organs to stretch and maintain protective lining
• Glandular epithelium - Endocrine glands

  • Function is secretion
  • Secretions of endocrine glands are called hormones
  • Secretions enter interstitial fluid and diffuse directly into bloodstream without flowing through a duct
  • Examples are pituitary gland, ovaries, thyroid, adrenal glands
• Glandular epithelium - Exocrine glands


  • Secretions released into ducts and empty onto a surface epithelium or lumen
  • Examples are sweat, oil earwax glands of skin, salivary glands
• Identifying epithelia - Human gall bladder

  • Simple columnar epithelium
• Identifying epithelia - Human nasal cavity

  • Ciliated pseudostratified columnar epithelium with goblet cells
• Identifying epithelia - Monkey ureter

  • Transitional epithelium
• Identifying epithelia - Integumentary - nipple


  • Stratified squamous epithelium
• Types of epithelial tissue

  • simple squamous
  • pseudostratified squamous
  • stratified squamous
  • simple cuboidal
  • pseudostratified cuboidal
  • stratified cuboidal
  • simple columnar
  • pseudostratified columnar
  • stratified columnar
  • transitional
  • Variable appearance
• Transitional epithelium


  • Almost exclusively lines urinary system - bladder, ureters and urethra
  • Allows urinary organs to stretch and maintain protective lining
• Glandular epithelium - Endocrine glands

  • Function is secretion
  • Secretions are called hormones
  • Secretions enter interstitial fluid and diffuse directly into bloodstream without flowing through a duct
  • Examples are pituitary gland, ovaries, thyroid, adrenal glands
• Glandular epithelium - Exocrine glands


  • Secretions are released into ducts and empty onto a surface epithelium or lumen
  • Examples are sweat, oil earwax glands of skin, salivary glands
• Summary of epithelium tissue locations

  • Human gall bladder - Simple columnar epithelium
  • Human nasal cavity - Ciliated pseudostratified columnar epithelium with goblet cells
  • Monkey ureter - Transitional epithelium
  • Integumentary - nipple - Sweat glands (arrow indicates basement membrane)
• Connective Tissues

  • Most abundant and widely distributed tissues in the body
  • Perform numerous functions: bind tissues together, support and strengthen tissue, protect and insulate internal organs, compartmentalise and transport, energy reserves and immune responses
  • Derived from mesenchyme - Immature cells have names that end in -blast, Mature cells have names that end in -cyte
• Features of connective tissues

  • Sparse cells
  • Extracellular matrix - non-cellular material located between and around the cells, consists of protein fibers and ground substance
  • Usually highly vascular and supplied with many nerves
  • Exception is cartilage and tendon - both have little or no blood supply and no nerves
• Fibroblasts


  Most numerous cell of connective tissues, large flat cells with branching processes, secrete protein fibers (collagen, elastin, & reticular fibers) and a "ground substance"