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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Calcified tissue international 22 (1976), S. 393-396 
    ISSN: 1432-0827
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Conclusions Our results indicate that both calcium intake and hormonal factors are important for the maintenance of bone structure. These findings might be relevant in setting up standards for calcium requirement.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Calcified tissue international 61 (1997), S. 104 -109 
    ISSN: 1432-0827
    Keywords: Key words: Calcitriol — Puberty — Bone mass — Osteocalcin — Adolescent females.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract. Adolescence is characterized by rapid skeletal development and high demands for bone minerals. Though the stimulative effect of calcitriol on intestinal calcium and phosphorus absorption is well understood, its effect on bone development is not completely clear. It may be directly involved in the facilitation of calcium economy during this critical phase of skeletal development. Therefore, we evaluated the serum concentrations of calcitriol in relation to skeletal development in a cross-sectional study of 178 healthy Caucasian females during different pubertal stages, extending from childhood to young adulthood. In addition, a subsample of 57 younger girls was followed for a 1-year period to evaluate the association among serum calcitriol, nutrition parameters (dietary calcium, phosphorus, and vitamin D), bone mass accumulation, and biochemical markers of bone turnover. The serum calcitriol concentration in a cross-sectional sample was the highest during pubertal growth spurt (sexual maturity index 3–4, age 11–13 years) (ANOVA: F = 2.4945; P= 0.0329). This correlated to the peak skeletal calcium accretion (g/year) and bone mass accumulation in total body and forearm. In a longitudinal sample, there was a positive association between annual change in TBBMC (P= 0.0255); TBBMD (P= 0.0168); proximal radius (1/3 distance from styloid process) BMC (P= 0.0096); BMD (P= 0.0541), and baseline calcitriol level in forward stepwise regression analyses. The results of the forward stepwise regression analyses with serum calcitriol as a dependent variable and different serum, urinary, and dietary parameters measured at baseline (age 11 years, n = 114) and after 1 year (age 12 years, n = 57) showed that osteocalcin was positively associated with calcitriol in both years; more so in a second year (P= 0.0514, P 〈 0.0001, respectively). Dietary vitamin D and phosphorus showed negative association with serum calcitriol at age 11, and dietary Ca and P were selected at age 12. The results of this study show that calcitriol is a significant correlate of bone mass accumulation during pubertal growth, presumably in response to the high requirements for calcium during this critical phase of skeletal development.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Osteoporosis international 3 (1993), S. 20-22 
    ISSN: 1433-2965
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Osteoporosis international 11 (2000), S. 985-1009 
    ISSN: 1433-2965
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Pflügers Archiv 375 (1978), S. 233-238 
    ISSN: 1432-2013
    Keywords: Calcium-45 kinetics ; Hydroxyproline ; Bone morphometry ; Age ; Sex
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The aim of this study was to establish the influence of age and sex on the kinetic and morphometric parameters of calcium metabolism. Normal values of kinetic parameters were determined in normal adult rats of different ages (4–20 months) and both sexes. Urinary hydrophyline excretion was also assessed and morphometric measurements of the femur were performed. Kinetic parameters expressed as rate constants showed a lowering of calcium turnover (k T) in the rapidly exchangeable calcium compartment until the age of 12 months and urinary and fecal rate constants (k u andk f ) showed a small increase. Males exhibited a lower calcium turnover (k T) as well as lower urinary and fecal rate constants. Hydroxyproline excretion diminished with age in both sexes. Lower values were recorded in males. Morphometric parameters of femurs showed no bone loss within the examined age. The results show that differences between the sexes exist in the sense of a faster calcium turnover, higher calcium excretion rate constants, higher collagen degradation and higher bone density in adult female rats.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Pflügers Archiv 375 (1978), S. 239-244 
    ISSN: 1432-2013
    Keywords: Calcium-45 kinetics ; Hydroxyproline ; Bone morphometry ; Ovariectomy ; Dietary calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The purpose of this work was to determine changes in calcium metabolism in the bone of adult rats caused by the deficiency of oestrogen hormones and a moderately low calcium intake. Kinetic parameters of calcium metabolism and some morphometric and chemical bone parameters were determined in female rats after ovariectomy and treatment with two levels of calcium in the diet (0.35% and 1%) for 2,4 and 6 months after the operation. Ovariectomy produced osteoporotic changes in the femurs which were enhanced in animals fed a low calcium diet. These changes were manifested by a larger medullary area and unchanged total midshaft area and resulted in lower cortical indices and lower quantity of ash per unit length of bone. Kinetic and balance studies showed a similar effect i. e. ovariectomized animals on the low calcium diet showed the lowest calcium balance values and the lowest calcium absorption rates. The highest bone resorption rates were also observed in ovariectomized animals on the low calcium diet. In our experiments oestrogen deficiency was a dominant factor in bone loss and calcium metabolism changes. It seems that a higher bone resorption and a lower calcium absorption due to a lack of oestrogens and lower calcium intake are the mechanisms which cause osteoporotic changes in bones.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1432-2161
    Keywords: Key words Bone mass ; Peak bone mass ; Skeletal age ; Pubertal stage ; Preadolescence ; Growth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Objective. To evaluate the association between chronological age, skeletal age, pubertal stage, and basic anthropometry with bone mass of the total body, forearm, and second metacarpal bone in 456 healthy Caucasian females, aged 8–13 years. Design. Total body and forearm bone measurements were performed by dual X-ray absorptiometry, while bone mass of the second metacarpal was assessed by radiogrammetry. Skeletal age (SA) was assessed by the FELS method and pubertal stage was self-determined by selecting corresponding illustrations of breast and pubic hair development. The C p criterion was used to select the best multiple regression model containing the subset of independent variables with the least bias and best predictive ability for each of the measured bone mass variables. Results. Of all the independent variables, weight, stature, and SA emerged as the most significant predictors for almost all the bone mass variables. Multiple regression models were created based on the C p criterion with the resulting R 2 (adjusted) for bone mineral content of total body, proximal forearm, ultradistal forearm, length of second metacarpal, as well as of total, medullary, and cortical areas: 0.793, 0.523, 0.390, 0.602, 0.232, 0.073, and 0.264, respectively. The measured bone variables were also regressed on SA using either quadratic or linear equations, depending on the shape of the cubic splines used for the best curve fitting. Significant positive association (p〈0.0001) of SA and each of the bone variables was noted, the highest being with bone mineral density and content of total body (R 2=0.176, 0.338) and proximal and ultradistal forearm (R 2=0.216, 0.203, 0.106, 0.201), respectively, as well as with the length of the second metacarpal bone (R 2=0.339). Chronological age and pubertal stage did not have statistically significant predictive abilities for bone mass variables in the multiple regression models. Conclusions. We conclude that skeletal age is a powerful determinant of bone mass in children. It can be used as the criterion for the selection of a biologically homogeneous population with regard to bone mass. This may be important for the design of intervention studies targeting bone mass of children and adolescents.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1435-1536
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Zusammenfassung 1. Es wird über Versuche berichtet, welche die Trennung des Rotschlamms von der Natriumaluminatlösung im Rahmen des Bayer-Verfahrens zum Gegenstand haben. Die Erscheinungen der schlechten Klärbarkeit des Schlamms sind auf keine Stoff-, sondern eine Zustandseigenschaft zurückzuführen. 2. Die Ursachen einer schlechten Klärung lassen sich aus dem Reaktionsmechanismus bei Aufschluß des Bauxits im Autoklaven ableiten. Aus der Kenntnis der Reaktionsmerkmale der einzelnen Umsetzungen lassen sich wesentliche Folgerungen für die technische Praxis ziehen. 3. Über die Wirkung des Mehls als Beschleuniger der Aggregierung in größere Aggregate werden zahlreiche Ergebnisse angeführt und auf den kolloidchemischen Charakter des Rotschlamms hingewiesen.
    Type of Medium: Electronic Resource
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