Learning objectives

Figure 7.1 Accrual of lean and fat mass during the prepubertal and pubertal periods. During adolescence, there is a rapid increase in the lean body mass of males and females, coinciding with the pubertal growth spurt. Fat mass also increases, but to a greater extent in females. Data redrawn from Guo et al. (1997) represents Caucasian children.

Table 7.1 Sexual maturation ratings (Tanner stages)

Figure 7.2 The relationship of growth velocity to pubertal staging in boys and girls. Average timings of pubertal (Tanner) staging are shown in the lower half of the figure. Age ranges beneath the pubertal staging boxes indicate the spread of values over which sexual maturation begins and ends. Height velocity curves at the top of the figure show the timings of the pubertal growth spurt in girls (____ ) and boys (- - - -) and the average age of maximal growth velocity. It is clear from the figure that in girls, acceleration of growth precedes pubertal development, while in boys, this acceleration occurs at a more advanced stage. (Source: Adapted from anner (1989).)

Figure 7. 3 The key endocrine events of adolescence Figure 7.3 The key endocrine events of adolescence. Adrenarche and puberty are separate processes that promote endocrine maturation. Development of the adrenal gland increases secretion of androgens in both males and females. The adrenal androgens stimulate development of secondary sexual characteristics. Puberty begins with the maturation of the hypothalamus and the stable rhythm of production of GnRH. FSH, follicle stimulating hormone; LH, luteinising hormone.

Figure 7. 4 The growth of long bones Figure 7.4 The growth of long bones. Long bones expand through activity within the epiphyseal growth plate, which lies at the interface of the bone shaft (diaphysis) and end (epiphysis). New cartilage cells (chondrocytes) are formed at the epiphyseal end of the growth plate, while mature cells on the diaphyseal end die and become calcified. The bone extends by virtue of this zone pushing the epiphysis away from the diaphysis.

Figure 7. 5 The accrual of bone mass Figure 7.5 The accrual of bone mass. Much of the mass of the adult skeleton is deposited during the adolescent growth phase. The most rapid rate of bone mineralization coincides with the pubertal growth spurt. Deposition of bone continues beyond the cessation of growth, and peak bone mass is achieved in the third decade of life.

Table 7.2 A comparison of nutrient requirementsa between adults and children aged 11–18 years

Table 7.3 Energy requirements of adolescents are dependent upon physiological development and physical activity level (PAL)

Figure 7.6 Factors that influence the food choices and eating behaviors of adolescents.

Research Highlight 7 Concerns surrounding nutrition and health in vegetarian adolescents

Table 7.4 Diagnostic criteria for eating disorders

Figure 7. 7 BN as a cycle of behavior driven by poor self-esteem Figure 7.7 BN as a cycle of behavior driven by poor self-esteem. Individuals with BN go through frequent episodes of binge eating followed by use of laxatives, emtics, or excessive exercise to compensate for ingested energy. The bingeing is seen as a way of dealing with anxiety and depression linked to poor self-esteem and feelings of low self-worth. Feelings of shame that follow the binge-purge episode actually serve to reinforce the initial problem and hence maintain the bulimic behavior.

Figure 7. 8 The metabolism of alcohol Figure 7.8 The metabolism of alcohol. Alcohol (ethanol) can be metabolized through cytosolic, microsomal, or peroxisomal pathways. Cytosolic metabolism involves the enzymes alcohol dehydrogenase (ADH) and acetaldehyde dehydrogenase 1 (ALDH1). Where the cytosolic capacity is exceeded, microsomal metabolism utilizes the cytochrome P450 enzymes (CYP2E1 and CYP4A1). Acetaldehyde products of microsomal ethanol metabolism are cleared by acetaldehyde dehydrogenase 2 (ALDH2). Peroxisomal catalase (CAT) can also contribute to alcohol clearance.

Summary Box 7

Self-Assessment Questions