Whole bones

Figure 7.5. Feedback diagram for skeletal mechanical regulation. When forces are applied to a whole bone, the stimulus that results is sensed by the bone cells in the tissue. The sensor cells then signal bone-forming and -removing cells to change the geometry and material properties of the bone.

In an earlier paper [31], the 15N values for two fractions of this bone was reported as -7.84 and -7.66 per mil. Analytical problems, which were unrecognized during the earlier measurements, have now been resolved. The average values for whole bone and for the organic extract listed in Table 5 are now considered to better represent the correct values. G. Rao, personal communication. 

There is a fundamental paradox in the physiology of bone mechanosensa-tion. The paradox (Figure 5) is that the strains applied to whole bone (i.e., tissue level strains) are much smaller (0.04 % to 0.3 %) than the strains (1 %... 

Figure 5. This figure illustrates the paradox addressed in mechanosensation. (a) An illustration of the small strains that the whole bone experiences, strains that are in the range 0.04 to 0.3 percent and seldom exceed 0.1 percent. The last two panels, (b) Photomicrograph of osteocytes encased in bone matrix (c) Osteocyte in lacuna, illustrate that large strains (1 to 10 percent) on cell membrane are needed to induce biochemical intracellular response in vitro. The paradox in the bone mechanosensing system is that the strains that activate the bone cells are two orders of magnitude larger than the strains to which the whole bone organ is subjected. Previously published in You et al. (2001).

Figure 7. Strain amplification A plot of the strain amplification ratio er as a function of the load frequency for different load magnitudes. Strain amplification ratio is defined as the ratio of the hoop strain in the cell process membrane to the bone surface strain at the osteonal lumen, e is the strain on the whole bone s is the load on the whole bone. Previously published in You et al. (2001).

Fig. 1. Atomic carbon and nitrogen values versus percent nitrogen in whole bone from two human cemetery samples. Pieces of human femurs from Archaic [7000 years before present (b.p.)] (squares) and historic (crosses) skeletons are shown. The nitrogen content is referenced to a contemporary compact bovine bone specimen (100%).

In the adult, new capillary blood vessels are normally not formed except in females, during ovulation, menstruation and pregnancy. Otherwise blood vessels remain quiescent. Endothelial cells which constitute the lining of the vessels divide slowly, if at all. Their turnover time may be as much as ten years. By contrast, other cell systems proliferate rapidly. For example, there are some 1010 cell divisions per hour in bone marrow, and the whole bone marrow mass is replaced in some five days. 

Finally, we have the whole bone itself constructed of osteons and portions of older, partially destroyed osteons (called interstitial lamellae) in the case of humans or of osteons and/or plexiform bone in the case of mammals. This we denote the macrostructural level The elastic properties of the whole bone results from the hierarchical contribution of each of these levels. 

Research groups interested in endothelial progenitor cells obtained CD34 stem cells from their patient donors using similar purification steps to those used for separating out mesenchymal stem cells from the whole bone marrow mononuclear stem cell population. In a phase I/IIa, single-bUnded, dose-escalation dial. 

Finally, the properties of a whole bone will be affected by the amounts of trabecular and cortical bone present and their geometric arrangement As will be discussed later, bone is a living tissue that... 

Out of print, new edition in preparation. Tries to deal with all aspects of mechanical properties of bone as a material and of whole bones. Not overly technical. Written from a general biological perspective, thus, does not concentrate on human material. 

---