Zahraa

• Connective Tissue is a group of cells and large amount of extracellular matrix
• Connective Tissue


  • Cells are widely separated from each other, unlike the epithelium cells which are tightly packed together by junctions
  • No cell junction between the cells in ordinary connective tissue
• Connective Tissue is the most abundant and widely distributed tissue type in the body
• Connective Tissues originate from embryonic mesenchyme
• Connective Tissue Vascularity


  • Avascular (Cartilage)
  • Poorly vascularized (dense connective tissue)
  • Rich blood supplies (bone)

  
• Connective Tissue Properties


  • Rigid (bone)
  • Flexible (adipose)
  • Fluid (blood)

  
• Connective Tissue does not occur on free surfaces
• Connective Tissue has a nerve supply (except cartilage)
• Functions of Connective Tissue

  • Support (mechanical and nutritional)
  • Defense and protection (contain inflammatory cells)
  • Storage (adipose tissue stores lipid)
  • Insulation
  • Transport (medium for gases and small molecules)
• Connective Tissue Components


  • Cell
  • Extracellular matrix (protein fibers, ground substance)
• Connective Tissue Resident Cells

  • Fibroblasts
  • Macrophages
  • Adipose cells
  • Mast cells
  • Undifferentiated mesenchymal cells

  
• Connective Tissue Wandering Cells

  • Lymphocytes
  • Plasma cells
  • Neutrophils
  • Eosinophils
  • Basophils
  • Monocytes

  
• Fibroblasts


  The most common cells in connective tissue, synthesize fibers and ground substance components

  
• Fibroblasts


  • Active fibroblast has more abundant and irregularly branched cytoplasm, large ovoid euchromatic nucleus with prominent nucleolus, abundant RER and well-developed Golgi
  • Quiescent fibroblast (Fibrocyte) is smaller, spindle-shaped with fewer processes, less RER, and more heterochromatic nucleus

  
• Fibroblasts are targets of growth factors that influence cell growth and differentiation
• Adipocytes


  Large mesenchymally derived cells specialized for cytoplasmic storage of lipid
• Macrophages


  • Well-developed phagocytic ability, specialize in turnover of protein fibers and removal of dead cells/debris
  • Large cells (10-30 μm) with many cell membrane projections, eccentrically located oval/kidney-shaped nucleus

  
• Macrophages


  Derive from bone marrow precursor cells, monocytes that circulate in blood and differentiate in connective tissue
• Macrophages play an important role in the early stages of repair after tissue damage
• Mast Cells


  Oval or irregularly shaped connective tissue cells, 7-20 μm in diameter, with cytoplasm filled with basophilic secretory granules

  
• Mast Cells


  • Originate from progenitor cells in bone marrow, function in localized release of bioactive substances like heparin, histamine, proteases, chemotactic factors, cytokines, and lipid mediators

  
• Mast cells are especially numerous near small blood vessels in skin and mesenteries, and in the tissue lining digestive and respiratory tracts

  
• Mast cell release of chemical mediators promotes the allergic reactions known as immediate hypersensitivity reactions
• Plasma Cells


  1. lymphocyte-derived, antibody-producing cells with basophilic cytoplasm rich in RER

  
• Leukocytes are derived from cells circulating in the blood, leave blood by migrating between endothelial cells to enter connective tissue

  
• Ground Substance


  Highly hydrated, transparent, complex mixture of glycosaminoglycans, proteoglycans, and multiadhesive glycoproteins that fills the space between cells and fibers
• Glycosaminoglycans (GAGs)


  Long, linear, unbranched polysaccharides consisting of repeating disaccharide units, usually a uronic acid and a hexosamine
• Major GAGs in Proteoglycans

  • Hyaluronan
  • Dermatan sulfate
  • Chondroitin sulfates
  • Keratan sulfate
  • Heparan sulfate
• Proteoglycans


  Composed of a core protein to which various GAGs are covalently attached
• Multiadhesive Glycoproteins


  Molecules comprising protein (integrins) and carbohydrate chains that connect cells to the extracellular matrix and guide their movements
• Integrins


  Integral membrane proteins that act as matrix receptors, mediating physical connections between ECM components and the cytoskeleton of cells
• Components of Tissues


  • Cells
  • Extracellular matrix (ECM)
  • Fibers
  • Organic and inorganic molecules
  • Water
  • Ground substance

  
• PREPARATION OF TISSUES FOR STUDY

  1. Fixation

  2. Embedding & Sectioning

  3. Staining
• Fixation


  The main functions are to avoid tissue digestion by enzymes, preserve cell and tissue structure, and prevent protein enzymes from functioning
• Fixation


  • Tissues are cut into small fragments before fixation to facilitate penetration and better ensure tissue preservation
  • Intravascular perfusion of fixatives can be used with some organs or laboratory animals to rapidly reach the tissues through the blood vessels
• Fixatives used


  • Buffered isotonic solution of 37% formaldehyde or 4% paraformaldehyde for light microscopy
  • Formaldehyde and glutaraldehyde, 4% paraformaldehyde for electron microscopy
  • Osmium Tetroxide for electron microscopy as a fixative and heavy metal stain

  
• Embedding & Sectioning


  1. Dehydration

  2. Clearing

  3. Infiltration

  4. Embedding

  5. Trimming
• Dehydration


  Water is extracted from the fixed tissues by successive transfer through a graded series of ethanol and water mixtures
• Clearing


  The ethanol is replaced by histoclear
• Infiltration


  Tissues are infiltrated with embedding materials like paraffin, plastic resins, or OCT compound