19 research outputs found
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Aging and Fracture of Human Cortical Bone and Tooth Dentin
Mineralized tissues, such as bone and tooth dentin, serve as structural materials in the human body and, as such, have evolved to resist fracture. In assessing their quantitative fracture resistance or toughness, it is important to distinguish between intrinsic toughening mechanisms which function ahead of the crack tip, such as plasticity in metals, and extrinsic mechanisms which function primarily behind the tip, such as crack bridging in ceramics. Bone and dentin derive their resistance to fracture principally from extrinsic toughening mechanisms which have their origins in the hierarchical microstructure of these mineralized tissues. Experimentally, quantification of these toughening mechanisms requires a crack-growth resistance approach, which can be achieved by measuring the crack-driving force, e.g., the stress intensity, as a function of crack extension ("R-curve approach"). Here this methodology is used to study of the effect of aging on the fracture properties of human cortical bone and human dentin in order to discern the microstructural origins of toughness in these materials
Valores de referencia para leptina, cortisol, insulina y glucosa entre los adolescentes europeos y su asociación con adiposidad: Estudio Helena
Background and Objective: Adequate concentrations
of leptin, cortisol, and insulin are important for a suitable
metabolism and development during adolescence. These
hormones jointly with glucose play a major role in fat
metabolism and development of childhood obesity. Our
main objective was to quantify biomarkers as leptin, cortisol,
insulin and glucose status in European adolescents
to contribute to establish reference ranges.
Methods: A representative sample of 927 adolescents
(45% males, 14.9±1.2 years for the overall population)
from ten European cities of the HELENA study was used
to obtain fasting blood samples for these biomarkers. The
percentile distributions were computed by sex and age
and percentiles were associated with BMI classification.
Results: Serum leptin concentration in adolescents
varied significantly according to BMI, sex and age (all
p<0.001). Cortisol presented a tendency to increase with
age, both for females and males, while insulin and glucose
were stable with age. Leptin and insulin were highest
in obese adolescents (p<0.001), whilst cortisol and glucose
did not vary with BMI. Percentiles 5, 25, 50, 75 and 95, 26.70 and 65.33 ng/ml for leptin; 5.00, 8.11, 11.14, 15.00
and 24.51 μg/dl for cortisol and 3.65, 6.15, 8.52, 11.90 and
20.53 μlU/ml for insulin.
Conclusions: In adolescents, leptin, cortisol, insulin
and glucose concentrations are differently affected by
age, sex and BMI. Establishment of reference ranges
(percentiles) of these biomarkers would be of great interest
when pediatricians have to assess the trend of an
adolescent to develop obesity years after.Objetivo: Concentraciones adecuadas de leptina, cortisol
e insulina son importantes para un metabolismo normal
durante la adolescencia, puesto que valores alterados
de estas hormonas, junto con la glucosa, se asocian con el
desarrollo de la obesidad infantil. Nuestro principal objetivo
fue cuantificar estos marcadores en adolescentes
europeos con el fin de establecer rangos de referencia.
Métodos: Muestras de sangre procedentes de 927 adolescentes
en ayunas (14,9 ± 1,2 años, 45% varones, estudio
HELENA), fueron analizadas para cuantificar la
leptina, cortisol, insulina y glucosa. Las distribuciones de
percentiles se determinaron teniendo en cuenta el sexo y
la edad. También se estudió la asociación entre percentiles
y la clasificación del IMC.
Resultados: La concentración de leptina en suero variaba
significativamente con el IMC, el sexo y la edad
(todos p<0,001). El cortisol presentó una tendencia a aumentar
con la edad, tanto para varones como mujeres,
mientras que la insulina y la glucosa eran estables con
la edad. La leptina y la insulina fueron más altas en los
adolescentes obesos (p <0,001), mientras que el cortisol y
glucosa no variaron con el IMC. Los percentiles 5, 25, 50,
75 y 95, para los valores de hormonas fueron, respectivamente:
1.27, 4.06, 11.54, 26.70 y 65.33 ng/ml para la leptina;
5.00, 8.11, 11.14, 15.00 y 24.51 μg/dl para el cortisol y
3.65, 6.15, 8.52, 11.90 y 20.53 μlU/ml de insulina.The HELENA study has taken place with the financial
support of the European Community Sixth
RTD Framework Programme (Contract FOODCT-
2005-007034). This study was also supported by a
grant from the Spanish Ministry of Science and Innovation
AGL2007-29784-E
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Microindentation for in vivo measurement of bone tissue mechanical properties in humans.
Bone tissue mechanical properties are deemed a key component of bone strength, but their assessment requires invasive procedures. Here we validate a new instrument, a reference point indentation (RPI) instrument, for measuring these tissue properties in vivo. The RPI instrument performs bone microindentation testing (BMT) by inserting a probe assembly through the skin covering the tibia and, after displacing periosteum, applying 20 indentation cycles at 2 Hz each with a maximum force of 11 N. We assessed 27 women with osteoporosis-related fractures and 8 controls of comparable ages. Measured total indentation distance (46.0 +/- 14 versus 31.7 +/- 3.3 microm, p = .008) and indentation distance increase (18.1 +/- 5.6 versus 12.3 +/- 2.9 microm, p = .008) were significantly greater in fracture patients than in controls. Areas under the receiver operating characteristic (ROC) curve for the two measurements were 93.1% (95% confidence interval [CI] 83.1-100) and 90.3% (95% CI 73.2-100), respectively. Interobserver coefficient of variation ranged from 8.7% to 15.5%, and the procedure was well tolerated. In a separate study of cadaveric human bone samples (n = 5), crack growth toughness and indentation distance increase correlated (r = -0.9036, p = .018), and scanning electron microscope images of cracks induced by indentation and by experimental fractures were similar. We conclude that BMT, by inducing microscopic fractures, directly measures bone mechanical properties at the tissue level. The technique is feasible for use in clinics with good reproducibility. It discriminates precisely between patients with and without fragility fracture and may provide clinicians and researchers with a direct in vivo measurement of bone tissue resistance to fracture
is a strong predictor of bone strength
The degree of bone mineralization is maintained with single intravenou