Trabecular bone

It is estimated that approximately 4% of compact bone is renewed annually in the typical healthy adult, whereas approximately 20% of trabecular bone is replaced. 

Picherit et al., 2000 1 yr old OVX rats oral administration, 90 d genistein or daidzein at 10 mg/kg body weight Overall daidzein > genistein in this study. Total femoral BMD losses and vertebral trabecular bone were protected by estradiol and daidzein, but genistein was not efficient. Bone strength (femoral failure stress) protected by estradiol, daidzein and genistein... 

Fig. 2.1.16 Trabecular bone structure, muscle after removal of the soft tissue (right). Image and tendon of a mouse tail in vitro at 21.14T, parameters multi-slice spin-echo method,...

K. Kose, Y. Matsuda, T. Kurimoto, S. Hashimoto, Y. Yamazaki, T. Haishi, S. Utsuzawa, H. Yoshioka, S. Okada, M. Add, T. Tsuzaki 2004, (Development of a compact MRI system for trabecular bone volume fraction measurements), Magn. Reson. Med. 52, 440—444. 

Osteopenia (80%) and osteoporosis, usually affecting trabecular bone... 

The human skeleton consists of both cortical and trabecular bone. Cortical bone is dense and compact and is responsible for much of bone strength. It is the most common type of... 

Under normal circumstances, the skeleton undergoes a dynamic process of bone remodeling. Bone tissue responds to stress and injury through continuous replacement and repair. This process is completed by the basic multicellular unit, which includes both osteoblasts and osteoclasts. Osteoclasts are involved with resorption or breakdown of bone and continuously create microscopic cavities in bone tissue. Osteoblasts are involved in bone formation and continuously mineralize new bone in the cavities created by osteoclasts. Until peak bone mass is achieved between the ages of 25 and 35, bone formation exceeds bone resorption for an overall increase in bone mass. Trabecular bone is more susceptible to bone remodeling in part owing to its larger surface area. 

Skeletal deposition is assumed to distribute into two pools 50% goes to the trabecular bone surface and 50% to the cortical bone surface. A first order rate coefficient for elimination of americium from liver to plasma is assumed to be 0.0019 day 1 (half-time, 365 days). 

Bone is divided into trabecular and cortical components, with each further divided into surface bone, bone volume, and bone cavity (marrow compartment). Deposition of americium is assumed to occur from plasma directly to bone surfaces, whereas elimination from bone occurs by transfer from the bone surface or volume to the marrow cavity, and then from the marrow cavity to plasma (Figure 3-6). Transfers of americium within the cortical or trabecular bone compartments are modeled based on assumptions about rates of bone formation and resorption, which are assumed to be vary with age, but are equal within a given age group (Leggett et al. 1982). Movement of americium to the marrow compartment is determined by the bone resorption rate, whereas, movement from the bone surface to the bone volume is assumed to occur by burial of surface deposits with new bone and is determined by the bone formation rate. During growth, bone formation and resorption are assumed to occur at different sites within bone therefore, the rate of removal of americium from the bone surface is approximated by the sum of the bone resorption rate (represented in the model by the movement of americium to the marrow compartment) and the rate of bone... 

Durbin and Schmidt (1985) proposed a model for tissue distribution and excretion of absorbed americium in humans. A unique feature of this model is that transfers from plasma to tissues are assumed to be instantaneous therefore, a central plasma (and blood) compartment is not included in the model (see Figure 3-10). Tissue compartments included in the model are slow and fast turnover bone compartments, representing cortical and trabecular bone, respectively liver and slow and fast turnover for other soft tissue compartments. Excretion pathways include urine and feces. Urinary excretion is represented as a sum of the contributions from bone, liver, and other soft tissues. Fecal americium is assumed to be excreted from the liver. 

DC, dendritic cell EC, endothelial cell EpC, epithelial cell FDC, follicular dendritic cell FDL, foot draining lymph FLS, fibroblast-like synoviocyte MC, mast cell MDDC, monocyte-derived dendritic cell MLS, macrophage-like synoviocyte MNC, mononuclear cell Mo, monocyte M0, macrophage OB, osteoblast pDC, plasmacytoid dendritic cell PMNs, polymorphonuclear neutrophils SC, stromal cell STC, synovium tissue cell TB, trabecular bone. 

Diffusible plasma / tissue / extravascular fluid / red blood cells / bound plasma (x103) / urinary bladder / urinary path /small intestine /trabecular bone surface / cortical bone surface / liver, rapid turnover rate / other kidney (x103) / other soft tissues, rapid turnover rate / other soft tissues, moderate turnover rate (x10) / other soft tissues, slow turnover rate (x102) / brain (x103) / sweat Bone / tissue (x103) 1,000 297-480 500-800 19-30 25-40 7.4-12.0 58-132 71-384 50-80 350-400 103-178 100-178 124-200 188-763 4.3-7.0... 

The toxicokinetics of lead in children appears to be similar to that in adults, with the exception of the higher absorption of ingested lead in children. Most of the lead body burden in both children and adults is in bone a slightly large fraction of the body burden in adults resides in bone (Barry 1975). The difference may reflect the larger amount of trabecular bone and bone turnover during growth trabecular bone has a shorter retention halftime for lead than does cortical bone (See Section 2.3.3 for details). 

Somervaille JL, Chettle DR, Scott, MC, et al. 1987. X-ray fluorescence of lead in vivo Simultaneous measurement of a cortical and a trabecular bone in a pilot study. In Ellis, Yasumuru, Morgan, eds. In vivo bodv composition studies. New York, NY Brookhaven National Laboratory, The Institute of Physical Sciences in Medicine. 

There are two types of bone (a) compact or cortical bone and (b) trabecular or cancellous bone. Cortical bone is found principally in the shafts (diaphyses) of long bones. It consists of a number of irregularly spaced overlapping cylindrical units termed Haversian systems. Each consists of a central Haversian canal surrounded by concentric lamellae of bony tissue. Trabecular bone is found principally at the ends of long bones and flat bones. It is composed of a meshwork of trabeculae within which... 

The skeleton consists of approximately 80 % cortical bone and 20 % trabecular bone, mainly in the axial skeleton. These amounts vary according to site and relate to the need for mechanical support. While trabecular bone accounts for the minority of total skeletal tissue, it is the site of greater bone turnover because its total surface area is greater than that of cortical bone. 

Mechanical and Degradation Properties. Studies characterizing the mechanical properties of these highly crosslinked materials indicate properties that are intermediate between those of cortical and trabecular bone. Table I summarizes these results along with the mechanical properties of bone. 

Skeleton Decreased trabecular bone density Rat ICI164384 (van Bezooijen et al. 1998)... 

Chow J, Tobias JH, Colston KW, Chambers TJ (1992) Estrogen maintains trabecular bone volume in rats not only by suppression of bone resorption but also by stimulation of bone formation. J Clin Invest 89 74-78... 

Turner RT, Wakley GK, Hannon KS, et al. (1988) Tamoxifen inhibits osteoclast mediated reabsortion of trabecular bone in ovarian deficient rat Endocrinology 122 1146-1150... 

Van Rietbergen B, Eckstein F, Roller B, et al. (2000) Trabecular bone tissue strains in the healthy and osteoporotic human femur. Orthopaed Res Soc 46 33... 

Akesson, K., Grynpas, M.D., Hancock, R. G. V., Odselius, R., and Obrant, K. J. (1994). Energy-dispersive X-ray-microanalysis of the bone mineral content in human trabecular bone - a comparison with ICP-ES and neutron-activation analysis. Calcified Tissue International 55 236-239. 

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