Bone Architecture and Remodeling in Relation to Stress
BONE ARCHITECTURE The architecture of the proximal femur beautifully illustrates the general principle that the external form and shape of bone as an organ and the internal organization of bone…
Stress-Generated Electric Potentials in Bone
BIOELECTRIC POTENTIALS IN BONE Bioelectric potentials are measured from the surface of nonstressed bone (see Plate 2-38). In the intact tibia, the metaphyseal and epiphyseal regions are net electronegative, whereas…
Musculoskeletal Effects of Weightlessness (Space Flight)
One consequence of space flight is a significant loss of bone mass (both matrix and mineral) in a weightless environment. During the early Gemini and Apollo flights, x-ray densitometry studies…
Effects of Disuse and Stress (Weight Bearing) on Bone Mass
Disuse osteoporosis may be focal, involving a single bone or limb (arthritis or limb immobilization), or it may be generalized (prolonged bed rest or paralysis). With generalized immobilization, bone loss…
Nutritional Calcium Deficiency
An intricate physiologic mechanism has evolved to prevent dangerous hypocalcemia: a reduction in calcium intake stimulates calcium absorption by the gastrointestinal tract, promotes renal calcium conservation, and stimulates net bone…
Normal Calcium and Phosphate Metabolism
1. Calcium phosphate is minimally soluble in water. In fact, at the pH of body fluids and the concentrations of calcium and phosphate ions found in extracellular fluids, the critical…
Four Mechanisms of Bone Mass Regulation
Example 7 shows the highly uncoupled state of increased bone formation and decreased bone resorption that result in a net increase in bone mass. Such a state of remodeling is…
Effects of Bone Formation and Bone Resorption on Skeletal Mass
Unless a significant metabolic insult occurs to bone early in life, the peak adult bone mass will exceed the threshold for spontaneous fracture. Noninvasive techniques to measure bone density have…
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…
