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Chapter 2

Chapter 2.doc

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Virginia K Walker

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Chapter 2 • Menarche- time of first period which is about age 12.5 • Puberty- comes from the latin word pubertas meaning adult, it is when one is capable of sexual reproduction. It has three physical functions: o Rapid increase in weight and height =growth o Development of primary sex characteristics, the gonads o Development of secondary sex characteristics, breast and pubic hair • Hormones are present before birth where some increase and others decrease • No new hormones are produced • Glands: organs that stimulate particular parts of the body to respond in specific ways to particular hormones. • Hormones carry messaged to particular cells in the body, and similarly cells are designed to receive hormonal messaged from particular hormones. • When a hormonal level in your body dips below the endocrine system’s set point, secretion of the hormone increases, and when the set point if reached, secretion stops. • The set point can be adjusted according to environmental or bodily conditions. • Hormonal Feedback loop: Gonadotropin releasing hormone neurons fire in the brain to increase a particular hormone. • HPG- feedback loop involving hypothalamus, pituitary, and gonads. o Pituitary – controls hormonal level in general o Hypothalamus- controls the pituitary gland, and has a concentration of GnRH neurons o Gonads- testes and ovaries, which release androgen and estrogen present in both sexes in different ratios/ levels. • The hypothalamus maintains levels of androgen and estrogen, and once they fall below set point, it does not inhibit the pituitary gland, thus allowing it to stimulate the release of sex hormones from the gonads and the adrenal glands. • Adrenarche- maturation of adrenal glands that happens before adolescence. The pituitary stimulates the thyroid and adrenal cortex to secrete hormones that cause body changes to take place at puberty. • Heightened vulnerability to stress because the hormonal changes of puberty make them more responsive to stress. • HPG axis is active before birth but is quiet until middle childhood when puberty occurs. • Puberty occurs only after a certain amount of body fat, leptin is accumulated and can be delayed by stress, illness, nutritional deficiencies, excessive exercise, and being thin. • Leptin tells the hypothalamus to stop inhibiting puberty, and GnRH neurons are activated. • Hormones play two roles: o Organization role- before birth, hormones organize brain in ways that are not active until adolescence. At 8 weeks, brain of a fetus is female by default unless it receives testosterone .The sex differences in brain organization predetermines certain behavior, which does not appear until later. Hormones program the brain in certain ways. o Organizational role of hormones: the process through which early exposure to hormones prenatally organizes the brain or other organs in anticipation of later changes in behavior or growth. o Activational role of hormones: the process through which changes in hormone levels especially at puberty stimulate changes in the adolescent’s behavior, appearance or growth. Somatic Development • Individual grows 10 inches taller, brain changes in size, structure and function. • Adolescence growth spurt occurs with the release of growth hormones, thyroid hormones and androgens that increases the speed at which growth occurs. • Peak height velocity: the time when the individual is growing the fastest , at the same rate as a toddler. • The conclusion of puberty is when the ends of the long bones are closing = a process called epiphysis which stops growth in height. • Growth spurt occurs 2 years earlier for girls than boys. • The increase in height results from an increase in torso length rather than leg length. Extremities, the head, hands and feets are the first to grow, then comes the arms and legs and then torso and shoulder. Their body is out of proportion because the parts of the body do not grow at the same rate during puberty. • Muscle tissue grows faster in boys than girls but body fat increases more for girls than boys just before puberty, and boys even decline in body fat before puberty= the reason for sex differences in athletic performance is due to hormonal imbalances because androgen increases in males at a faster rate than in females which influences growth. • Sex differences in body fat can also result for environmental factors such as little physical activity for girls, and poor nutrition. • Those who mature early, dating early, and come from more affluent families start dieting early as well – feelings of dissatisfaction. This differs b/w ethnicity because black girls don’t diet are less vulnerable. • Secondary sex characteristics: manifestations of sexual maturity at puberty, including the development of breast, facial and body hair and changes in the voice. • Tanner stages: describes the 5 stages of pubertal development/ secondary sex characteristics and sexual maturation is measured according to the tanner stages. • It is in order for boys. It involves: growth of testes and scrotum, pubic hair, growth spurt, growth of penis and more pubic hair (darker colour). The are changes in the skin, it becomes rougher, around the arms and thighs and increased sweat glands which gives rise to acne and pimples. Voice deepening occurs during late adolescence. Breast development is influenced by the estrogen hormone where the areola ( are around the nipple) increases in size. • Boys are capable of fathering a child/ fertile before they look like an adult. • It is less regular for girls. First, breast grows then pubic hair, then body, and after menarche occurs. Then underarm hair and sweat glands. • The size of the breast does not matter in indicating sexual maturation, it is the areolar and the nipple growth that matters. • Development of reproductive capacity includes growth of uterus, vagina, enlargement of labia and clitoris. • Ovulation follows menarche about 2 years after so girls look mature before they are fertile or can be mothers. Timing and Tempo of Puberty • Timing and rate of maturation varies greatly b/w 7 in girls and 9 in boys to 13 in girls and 13.5 in boys. An early and fast maturing adolescent can complete pubertal maturation way before a later mature and before late and slow maturer. • Late maturer- being somewhat taller • Early mature- somewhat heavier • The timing and tempo of an individual’s pubertal maturation is largely inherited according to twin studies. Environment’s role is that it determines exactly when an individual goes through puberty while genetic factors are predispositions thought of as an upper and lower age limit. Environmental factors are nutrition and health. Puberty occurs earlier for those who are better nourished at younger ages, but chronic illness or excessive exercise can delay puberty. • Puberty also occurs early for girls who grow up in a household without a
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