Morphological and physiological changes during growth: an update

Abstract

Skeletal growth and changes in body composition during growth present important variations; body mass index and lean body mass related to age show important gender differences. The process of ossification is developed in two different ways, endochondral and intramembraneous. The former is characterised by the formation of bone from growth cartilage. Intramembraneous ossification is characterised by the formation of bone from a mesenchymal structure, as occurs with the flat bones of the skull. During childhood and adolescence and up to the acquisition of adult stature, two phenomenons are produced simultaneously: the synthesis of new bone from growth cartilage due to the process of endochondral ossification, and modeling-remodeling of previously synthesized bone. Bone growth and mineralisation of its extracellular matrix are simultaneous phenomenons, the final result being the acquisition and maintenance of body bone mass. A positive calcium balance is necessary during adolescence in order to achieve the maximum peak of bone mass and even with the termination of longitudinal growth of bone, the process of mineralisation can last a further 4 years. Childhood and adolescence are the period of life in which the peak of bone mass must be achieved, and if during this time this does not happen there will be a greater risk for the later development of osteoporosis. Regulation of bone mass is a polygenic process and during recent years studies have been centred on the receptor genes of vitamin D and estrogens. A maximum calcium retention during adolescence may influence the achievement of a high peak of bone mass but at a certain level of calcium intake the calcium retention reaches a plateau. The expression of grams of hydroxyapatite per square centimetre has been used clinically, or expressed in volume as g/cm3. From birth until 3 years, the increase represents approximately 30% of the total increase, from 3 years until the beginning of pubertal development the increase is 20%. During pubertal development there is an increase of 30-40% and from the end of growth until the age of 21 years there is an increase of 15-20%. Both prepubertal boys and girls show a progressive increase of leptin levels during the years prior to the onset of puberty and until Tanner's stage 11 and higher levels are observed in girls in this period, possibly in relation to their earlier onset of puberty. This increase of leptin in girls during pubertal development suggests that leptin may be a link between adipose tissue and puberty.

Incomplete Endochondral Ossification of the Otic Capsule, A Variation in Children: Evaluation of Its Prevalence and Extent in Children with and without Sensorineural Hearing Loss

“…In this study, the iEO was similar among the 2 sexes but, as expected, had an inverse correlation with age. This finding is in agreement with previously mentioned series reporting that the OC ossification is correlated with the age of the individual rather than the sex but is somewhat controversial due to the established knowledge of delayed bone maturation in males, 18 and our results may be because the area of concern is very small and minor differences are difficult to detect. Asymmetric EO among the contralateral ears was found in 74 patients without a sex or age predilection (P ϭ .8 and P ϭ 1, respectively).…”

Leptin stimulates human osteoblastic cell proliferation, de novo collagen synthesis, and mineralization: Impact on differentiation markers, apoptosis, and osteoclastic signaling

“…Our findings are substantiated by the very recent report by Bassilana et al (2000), demonstrating that human mesenchymal stem cells, when differentiated, express leptin and leptin receptor isoforms, as well as leptin-induced phosphorylation of STAT3. In the light of the localization of leptin and its receptor isoforms in osteoblastic cells, it is not surprising that an accumulating number of publications demonstrate that leptin stimulates bone formation [Liu et al, 1997;Goulding and Taylor, 1998;Iwaniec et al, 1998;Huang and Li, 2000;Steppan et al, 2000], and that circulating leptin levels may be associated with bone mass in young individuals [Matkovic et al, 1997;Klein et al, 1998;Ballabriga, 2000]. Finally, human bone marrow adipocytes have been shown to synthesize leptin [Laharrague et al, 1998].…”

Effects of usual nutrient intake and vitamin D status on markers of bone turnover in Swiss adolescents

“…The different patterns observed for both bone markers in boys and girls are probably attributable to the earlier onset of puberty in girls (Ballabriga, 2000). Although the mean age of boys and girls at P2 was similar, the rate of change is known to be slower in boys, with P2 occurring after genital development stage 3 in boys, compared to breast development stage 2 in girls (Tanner, 1963).…”