Connective Tissue

• Connective tissue is specialized to physically support and connect other tissues and maintain the water required for metabolite diffusion to and from cells.
• Connective tissue cells are scattered throughout the extracellular matrix (consists of large protein fibers and glycoproteins attached to the basement membrane)
• Epithelial tissues cells form a sheet-like structure or lines our organ
• All connective tissue has 3 components

  I. Cells

  II. Ground Substance

  III. Fibers
• Major constituent of connective tissue is the extracellular matrix (ECM)
• • the major cells of connective tissue proper
  • elongated, irregularly shaped cells with oval nuclei that synthesize and secrete most components of the ECM.

  FIBROBLASTS
• target of many families of proteins called growth factors that influence cell growth and differentiation
• Fibroflast has more abundant and irregular branched cytoplasm, containing much RER, and a well developed Golgi apparatus, with a large, ovoid, euchromatic nucleus and prominent nucleolus
• inactive form of fibroblast

  • smaller and usually spindle shaped with fewer processes, much less RER and a darker and more heterochromatic nucleus


  Fibrocyte (Quiescent cell)
• • very large cells specialized for storage of triglycerides
  • they predominate in a specialized form of connective tissue called adipose tissue


  adipocytes (fat cells)
• • this is the embryologic tissue from which all types of supporting/connective tissue are derived
  • relatively unspecialized and are capable of differentiation into all supporting tissue cell types
  • have an irregular,star(stellate) or spindle (fusiform) shape with delicate branching cytoplasmic extensions which form an interlacing network throughout the tissue 


  mesenchymal cells
• • phagocytic cells
  • short lived cells that differentiate in connective tissue from precursor cells called monocyte
  • function in ECM turnover, phagocytosis of dead cell and debris, and antigen presentation to lymphocytes; secretion of growth factors, cytokines and etc
  • "histiocytes"

  Macrophages
• LOC: blood

  FUNCTION: precursor of macrophages

  MONOCYTE
• LOC: Connective tissue, lymphoma organs, lungs, bone marrow, pleural and peritoneal cavities

  FUNCTION: production of cytokines, chromatic factors and molecules to participate in inflammation (defense), antigen processing and presentation
• LOC: liver (perisinusoidal)

  FUNCTION: production of cytokines, chromatic factors and molecules to participate in inflammation (defense), antigen processing and presentation 


  KUPFFER CELL
• LOC: CNS

  FUNCTION: production of cytokines, chromatic factors and molecules to participate in inflammation (defense), antigen processing and presentation 


  MICROGLIAL CELL
• LOC: Epidermis of skin

  FUNCTION: Antigen processing and presentation

  LANGERHAN CELL
• LOC: Lymph nodes and spleen

  FUNCTION: antigen processing and presentation

  DENDRITIC CELL
• LOC: Bone

  FUNCTION: Localized digestion of bone matrix

  O (from fusion of several macrophages)
• LOC: in connective tissue under various pathological conditions

  FUNCTION: segregation and digestion of foreign bodies


  MULTINUCLEAR GIANT CELL (several fused macrophages)
• originate from blood cell precursor and are filled with granules for the release of various vasoactive agents and other substances during inflammatory and allergic rxn

  MAST CELLS
• • short lived cells that differentiate form B lymphocytes and are specialized for the abundant secretion of specific antibodies
  • immunoglobulins

  PLASMA CELLS
• • providing surveillance against bacterial invaders and stimulating tissue repair
  • WBC

  LEUKOCYTES
• • not normal components of the connective tissue
  • migrate to connective tissue to act as a response during inflammation
  • in response to tissue damage

  WANDERING/ TRANSIENT CELLS
• fixed or resident cells

  • Mesenchymal cells
  • Fibroblast/ Fibrocyte, Adipocyte
• • clear area of the connective tissue
  • an amorphous transparent material with the physical character of semi sold gel that fills the space
  • mixture of glycoproteins and complex carbohydrates with profound water b ability

  GROUND SUBSTANCE
• • are long polymers of repeating disaccharide units, usually a hexosamine and uronic acid

  GLYCOSAMINOGLYCANS
• • Glucosaminoglycans' most abundant; largest; most ubiquitous

  HYALURONATE
• • consist of a core protein to which are covalently attached various numbers and combinations of the sulfates GAGS
  • bind to hyaluronic acid producing massive quaternary structures, others interact with collagen or bind to other matrix molecules including remodeling enzymes, enzyme inhibitors, growth factors, cytokines, and cell surface receptors

  PLASMA CELLS
• large, core protein heavily bound with chondroitin and keratan sulfate chain.

  AGGRECAN
• key proteoglycan in all basal laminae


  PERLECAN
• • all have multiple binding sites for cell surface integrins and for other matrix macromolecules
  • water in the ground substance of connective tissue is refereed to as an interstitial fluid and has an ion composition similar to that of blood plasma

  MULTIADHESIVE/ STRUCTURAL GLYCOPROTEINS
• binding sites for collagen and certain GAGs, and forms insoluble fibrillar networks throughout connective tissue

  FIBRONECTIN
• with binding sites for integrins, type IV collagen, and specific proteoglycans; providing adhesion for epithelial and other cells; component of the basal lamina

  LAMININ
• collagen, reticular fiber, and elastic fibers are

  FIBERS
• • main fibre type found in most supporting tissues
  • most abundant protein in human body

  COLLAGEN
• • originate from collagen III
  • stain poorly in H&E preparation
  • form delicate supporting FW for many cellular organs such as endocrine glands, lymph nodes, bone marrow, and liver

  RETICULAR FIBERS
• • arranged as fibers/ discontinuous sheets in te extracellular matrix (elastic lamellae) where it confers the properties of stretching and elastic recoil
  • composed of proteins Elastin and Fibrilin, which exist in a stretchable conformation that provides elastic properties to connective tissue

  ELASTIC FIBER
• Type of Collagen

  1, 2, 3, 4, 7
• • most abundant
  • main structural collagen and is found in fibrous supporting tissue, skin
  • visible with light microscope
  • staining pink with H&E 


  TYPE I COLLAGEN