Bone Matrix

• In contrast, IL-10 suppresses osteoclasts.

  • Organic components: 40% of dry weight of bone

    • Collagen (90% of organic components)

      • Primarily type I (mnemonic: bone

        contains the word one)

        • Type I collagen provides tensile strength of bone

      • Hole zones (gaps) exist within the collagen fibril between the ends of molecules.

      • Pores exist between the sides of parallel molecules.

      • Mineral deposition (calcification) occurs within the hole zones and pores.

         

         

        FIG. 1.4 Control and function of the osteoclast. Vit,

        vitamin.

         

    • Cross-linking decreases collagen solubility and increases its tensile strength.

    • Proteoglycans

    • Matrix proteins (noncollagenous)

      • Osteocalcin: most abundant noncollagenous protein in bone

        • Inhibited by PTH and stimulated by 1,25(OH)2D3

        • Can be measured in serum or urine as a marker of bone turnover

      • Inorganic (mineral) components: 60%

•  Bone Matrix (Table 1.3)

  • Found in membranes surrounding loose total joint implants

 

• Tissues surrounding bone

  • Periosteum

of dry weight of bone

• Calcium hydroxyapatite [Ca 10 (PO 4 ) 6 (OH) 2 ]:

  provides compressive strength

• Calcium phosphate (brushite)

  • Connective tissue membrane that covers bone

  • More highly developed in children

  • Inner periosteum, or cambium, is loose and vascular and contains cells capable of becoming osteoblasts.

    • These cells enlarge the diameter of bone during growth and form periosteal callus during fracture healing.

  • Outer (fibrous) periosteum is less cellular and is contiguous with joint capsules.

  • Bone marrow—source of progenitor cells; controls inner diameter of bone

    • Red marrow

      • Hematopoietic (40%

        water, 40% fat, 20% protein)

      • Slowly changes to yellow marrow with age, first

        in appendicular skeleton and later in axial skeleton

  • Yellow marrow

 

• Inactive (15% water, 80% fat, 5% protein)

 

 

Table 1.3

Components of Bone Matrix

 

 

Type of Matrix	Function	Composition	Types	Notes
Organic Matrix
Collagen	Provides tensile strength	Primarily type I collagen		Con

				Stru
Proteoglycans	Partly responsible for compressive strength	Glycosaminoglycan-protein complexes		Inhibit
Matrix proteins Promote (noncollagenous) mineralization and bone formation			Osteocalcin (bone γ- carboxyglutamic acid–containing protein) Osteonectin (SPARC)	Attr   Sec
			Osteopontin	Cell-bi sim inte
Growth factors and cytokines	Aid in bone cell differentiation, activation, growth, and turnover		TGF-β IGF IL-1, IL-6 BMPs	Present am mat
Inorganic Matrix
Calcium hydroxyapatite [Ca10(PO4)6(OH)2]	Provides compressive strength			Most o mat min coll (hol seco min peri

Osteocalcium phosphate (brushite)

Makes rem inor