Connective Tissue

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Definition:

Connective tissue comprises cells that lay down proteins and glycoconjugates (glycoproteins, proteoglycans, glycosaminoglycans) within an insoluble extracellular matrix. Connective tissue includes skin, ligaments, tendons, bone, synovial fluid, vitreous gel, walls of blood vessels, and cartilage. Virtually all structures in the body contain connective tissue. Cells within connective tissue, along with those of the immune system, secrete specific enzymes important during injury, infection, and allergy. These enzymes (broadly known as hydrolases) serve to breakdown the protein and glycoconjugate structures.

Composition:

  • Collagens
    - most abundant protein family
    - more than 19 types
  • Elastin
  • Fibrillin
    - major component of 10-nm microfibrils
    - genes located on chromosomes 5 and 15
    - genetic defects lead to ectopia lentis, congenital contractural arachnodactyly, Marfan syndrome
  • Fibronectin
  • Laminin
  • Nidogen
  • Proteoglycans

Constituents of Connective Tissue

 Connective tissue  Constituents
 Skin, ligaments, tendons  Types I, III, IV, V, VI, and VII collagens
 Elastin, fibrillin, fibronectin
 Laminin, nidogen
 Proteoglycans and hyaluronate
 Demineralized bone  Types I, VI collagens
 Proteoglycans
 Osteonectin, osteocalcin, osteopontin
 alpha2-glycoprotein, sialoproteins
 Aorta  Types I, III, IV, V, and VI collagens
 Elastin, fibrillin, laminin, nidogen
 Proteoglycans
 Cartilage  Types II, IX, X, and XI collagens
 Proteoglycans and hyaluronate

Processing Enzymes:

 lysyl hydroxylase
 type I procollagen N-proteinase
 procollagen C-proteinase
 collagenase
 proline hydroxylase
 lysyl oxidase
 collagen glycosyltransferase
 collagen galactosyltransferase
 disulfide isomerase
 prolyl cis-trans isomerase
 sulfotranferase
 elastase

 

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