Bone balance within a cortical BMU: Local controls of bone resorption and formation

Maintaining bone volume during bone turnover by a BMU is known as bone balance. Balance is required to maintain structural integrity of the bone and is often dysregulated in disease. Consequently, understanding how a BMU controls bone balance is of considerable interest. This paper develops a methodology for identifying potential balance controls within a single cortical BMU. The theoretical framework developed offers the possibility of a directed search for biological processes compatible with the constraints of balance control. We first derive general control constraint equations and then introduce constitutive equations to identify potential control processes that link key variables that describe the state of the BMU. The paper describes specific local bone volume balance controls that may be associated with bone resorption and bone formation. Because bone resorption and formation both involve averaging over time, short-term fluctuations in the environment are removed, leaving the control systems to manage deviations in longer-term trends back towards their desired values. The length of time for averaging is much greater for bone formation than for bone resorption, which enables more filtering of variability in the bone formation environment. Remarkably, the duration for averaging of bone formation may also grow to control deviations in long-term trends of bone formation. Providing there is sufficient bone formation capacity by osteoblasts, this leads to an extraordinarily robust control mechanism that is independent of either osteoblast number or the cellular osteoid formation rate. A complex picture begins to emerge for the control of bone volume. Different control relationships may achieve the same objective, and the ‘integration of information’ occurring within a BMU may be interpreted as different sets of BMU control systems coming to the fore as different information is supplied to the BMU, which in turn leads to different observable BMU behaviors

4-H 223 Clothing : Level I

Extension Service 4-H 223: Clothing level 1; Evaluation sheet, what you do in the project, requirements, fabric, picking a pattern, body measurements, preparing the fabric for cutting, from fiber to fabrics, the sewing machine, serger machine, sewing basics, interfacing, seams, under stitching, hems, you and your appearance, clothing care, modeling tips, and how do you rate

Theoretical analysis of the spatio-temporal structure of bone multicellular units

Bone multicellular units (BMUs) maintain the viability of the skeletal tissue by coordinating locally the sequence of bone resorption and bone formation performed by cells of the osteoclastic and osteoblastic lineage. Understanding the emergence and the net bone balance of such structured microsystems out of the complex network of biochemical interactions between bone cells is fundamental for many bone-related diseases and the evaluation of fracture risk. Based on current experimental knowledge, we propose a spatio-temporal continuum model describing the interactions of osteoblastic and osteoclastic cells. We show that this model admits travelling-wave-like solutions with well-confined cell profiles upon specifying external conditions mimicking the environment encountered in cortical bone remodelling. The shapes of the various cell concentration profiles within this travelling structure are intrinsically linked to the parameters of the model such as differentiation, proliferation, and apoptosis rates of bone cells. The internal structure of BMUs is reproduced, allowing for experimental calibration. The spatial distribution of the key regulatory factors can also be exhibited, which in diseased states could give hints as to the biochemical agent most accountable for the disorder

Life path analysis: scaling indicates priming effects of social and habitat factors on dispersal distances

1. Movements of many animals along a life-path can be separated into repetitive ones within home ranges and transitions between home ranges. We sought relationships of social and environmental factors with initiation and distance of transition movements in 114 buzzards Buteo buteo that were marked as nestlings with long-life radio tags. 2. Ex-natal dispersal movements of 51 buzzards in autumn were longer than for 30 later in their first year and than 35 extra-natal movements between home ranges after leaving nest areas. In the second and third springs, distances moved from winter focal points by birds that paired were the same or less than for unpaired birds. No post-nuptial movement exceeded 2 km. 3. Initiation of early ex-natal dispersal was enhanced by presence of many sibs, but also by lack of worm-rich loam soils. Distances travelled were greatest for birds from small broods and with relatively little short grass-feeding habitat near the nest. Later movements were generally enhanced by the absence of loam soils and short grassland, especially with abundance of other buzzards and probable poor feeding habitats (heathland, long grass). 4. Buzzards tended to persist in their first autumn where arable land was abundant, but subsequently showed a strong tendency to move from this habitat. 5. Factors that acted most strongly in ½-km buffers round nests, or round subsequent focal points, usually promoted movement compared with factors acting at a larger scale. Strong relationships between movement distances and environmental characteristics in ½-km buffers, especially during early ex-natal dispersal, suggested that buzzards became primed by these factors to travel far. 6. Movements were also farthest for buzzards that had already moved far from their natal nests, perhaps reflecting genetic predisposition, long-term priming or poor habitat beyond the study area

Prolonged bouts of sedentary time are associated with 2-hr plasma glucose, independent of total sedentary time

The Conference will be held concurrently with the 2007 Recreation and Sport Development Conference, the Australian Conference of Science and Medicine in Sport, and the 5th National Sports Injury Prevention Conference.Total sedentary time is associated with increased 2-hr plasma glucose. However, total sedentary time does not indicate how the sedentary time was accumulated. Animal studies suggest that longer, uninterrupted bouts of sedentary time have more detrimental metabolic effects compared with shorter accumulated bouts. We examined if longer average bouts of sedentary time were associated with higher 2-hr plasma glucose, independent of total sedentary time. In total, 67 men and 106 women (mean age 53.3, range 30 to 87) without known diabetes were recruited from the 2004-2005 AusDiab study. Sedentary time was measured by accelerometers worn during waking hours for seven consecutive days, and summarised as total sedentary time (counts/minute < 100, hours), total number of sedentary bouts, and mean sedentary bout time (minutes). A sedentary bout was defined as the sum of minutes of <100 accelerometer counts. An oral glucose tolerance test determined 2-hr plasma glucose. Mean sedentary bout time was 6.0 minutes (range 3.0 to 11.3). After adjusting for age, sex, total sedentary time, moderate-to-vigorous intensity physical activity, and time accelerometer worn, mean sedentary bout time was significantly associated with higher 2-hr plasma glucose (b=0.28, 95%CI 0.07 to 0.49, p=0.010). Additionally, total number of sedentary bouts (reflecting more breaks in sedentary time) was significantly associated with lower 2-hr plasma glucose (b=-0.04, -0.06 to -0.01 per 10 bouts, p=0.003). These findings provide preliminary evidence on the potential importance for human health of avoiding prolonged periods of being sedentary, and provide a key step towards formulating sedentary behaviour recommendations.The 6th National Physical Activity Conference (be active ‘07), Adelaide, Australia, 13-16 October 2007. In Journal of Science and Medicine in Sport, 2007, v. 10, suppl. 1, p. 60, abstract no. 16

Theoretical investigation of the role of the RANK–RANKL–OPG system in bone remodeling

The RANK–RANKL–OPG system is an essential signaling pathway involved in bone cell–cell communication, with ample evidence that modification of the RANK–RANKL–OPG signaling pathway has major effects on bone remodeling. The first focus of this paper is to demonstrate that a theoretical model of bone cell–cell interactions is capable of qualitatively reproducing changes in bone associated with RANK–RANKL–OPG signaling. To do this we consider either biological experiments or bone diseases related to receptor and/or ligand deficiencies, including RANKL over-expression, ablation of OPG production and/or RANK receptor modifications. The second focus is to investigate a wide range of possible therapeutic strategies for re-establishing bone homeostasis for various pathologies of the RANK–RANKL–OPG pathway. These simulations indicate that bone diseases associated with the RANK–RANKL–OPG pathway are very effective in triggering bone resorption compared to bone formation. These results align with Hofbauer's “convergence hypothesis”, which states that catabolic bone diseases most effectively act through the RANK–RANKL–OPG system. Additionally, we demonstrate that severity of catabolic bone diseases strongly depends on how many components of this pathway are affected. Using optimization algorithms and the theoretical model, we identify a variety of successful “virtual therapies” for different disease states using both single and dual therapies