Dynamics of Bone Homeostasis
Calcium Requirements. The body regulates few functions with greater fidelity than the concentration of ionized calcium in the extracellular fluid. Although extracellular calcium represents less than 1% of the body’s…
Regulation of Calcium and Phosphate Metabolism
The exchange of calcium between extracellular fluid and bone can be considered kinetically (see Plate 2-28). Through a slow phase of bone formation and resorption, approximately 1000 mg/day of calcium…
Histology of Connective Tissue
Regardless of its histologic type, connective tissue is made up of two components, cells and extracellular matrix. Fibroblasts (which synthesize collagen), fat cells, fixed macrophages, mast cells, plasma cells, and…
Structure and Function of Synovial Membrane
On gross examination, the synovial surface appears pale pink and shiny. Although some folds can be seen with the naked eye, the characteristic villi that increase the effective surface area…
Formation and Composition of Proteoglycan
To make the situation even more complex, aggrecans form aggregates with two other matrix components—hyaluronan and link proteins. This aggregate consists of a variable number of proteoglycan monomers, depending on…
Formation and Composition of Collagen
Like members of most families, the collagens share certain similarities but also possess characteristic differences. To date, 28 types of collagen macromolecules have been identified. The most abundant, type I…
Structure of Trabecular Bone
In actively growing, or remodeling, trabecular bone, the direction of deposition can be determined by a row of osteoblasts on one border of the trabecula (see Plate 2-23). The deposition…
Structure of Cortical (Compact) Bone
Cortical bone is remodeled by on the periosteal, endosteal, and haversian canal surfaces. These surfaces are called bone envelopes, or remodeling bays. The periosteal surface is responsible for the growth…
Composition of Bone
Mature lamellar bone has the same chemical composition and material properties throughout the skeleton, regardless of its mechanism of formation—intramembranous or endochondral—or its structural organization—cortical (compact) or trabecular bone. Skeletal…
Bone Cells and Bone Deposition
The osteoblast, or bone-forming cell, is approximately 20 µm in diameter and contains a single eccentric nucleus. Under the direction of RUNX2 and Osterix transcription factors, osteoblasts arise from osteoprogenitor…
