collagen types
      Type I 
        – major collagen type, fibrous, ranging from loose to dense, found in tissues varying from skin, to tendon, to bone 
      Type III 
        – “reticular fibers” – delicate, branching fiber forming a supportive scaffold for various organ structures 
      Type IV 
        – mesh-like, sheet-forming type of collagen found in the basement membranes of various epithelia 
      Type V 
        – form of collagen important in organizing connective tissues, found in placental, fetal, and interstitial tissue