Figure 5. Schematic Representation of the Cellular and Skeletal Sources of Serum and/or Urinary Markers of Bone Formation and Bone Resorption. Abbreviations: BGP, bone gamma carboxyglutamic acid (GLA) protein (osteocalcin); PICP, C-terminal propeptide of type I procollagen; P1NP, N-terminal propeptide of ty pe I procollagen; BAP, bone-specific alkaline phosphatase; AP, alkaline phosphate; TRAP, tartrate-resistance acid phosphatase; NTX, N-terminal cross-linked telopeptide of type I collagen; CTX, C-terminal cross-linked telopeptide of type I collagen; OH, hydroxyproline glycoside; OL, hydroxylysine glycoside; PYD, pyridinoline (total, free); DPD, deoxypyridinoline (total, free). (see Acknowledgments).