Chapter 14: Physical Development in Adolescence
What is the sequence of events in sexual maturation in boys?
Enlargement of testes, changes in texture/color of scrotum, pubic hair, penis enlargement, later growth spurt (longer-lasting and intense growth spurt) with facial/body hair emerging after peak in body growth and deepening of voice, spermarche (first ejaculation)
What is the secular trend?
The tendency in recent centuries for puberty to occur at younger ages; thought it is slowed overall, obesity rates in US continue trend of earlier menarche
What is adolescence?
The transition between childhood and adulthood
What is puberty?
A flood of biological events that marks the beginning of adolescents and leads to an adult-sized body and sexual maturity
How and why do parent-child relationships change during adolescence?
Children, in becoming physically mature, demand to be treated in adult-like ways. Adolescents' new powers of reasoning may also contribute to a rise in family tensions. Parent-adolescent disagreements focus largely on everyday matters like driving, dating, and curfews. But beneath lie serious concerns: parental efforts to protect teens from substance use, auto accidents, and early sex. The larger the gap between parents' and adolescents' views of teenagers' readiness for new responsibilities, the more they quarrel
What is menarche?
First menstruation occurring relatively late in sequence of pubertal events around 12 1/2 for girls in NA., but ranges from 10 1/2 to 15 1/2. It is followed by breast and pubic hair growth completing and underarm hair appearing. Nature delays sexual maturity until girl's body is large enough for childbearing.
How do states of arousal and sleep change in adolescence?
Increased neural sensitivity to evening light makes adolescents go to bed much later than they did as children, although they need almost as much sleep as they did in middle childhood (9 hours). Inconsistency with an early school day strengthens with pubertal growth. Sleep rebound on weekends sustains the pattern by leading to difficulty falling asleep on subsequent evenings. Later school times ease but do not eliminate sleep loss; educating teens is vital.
What hormonal changes occur during adolescence?
Secretion of GH and thyroxine increase. Both estrogens and androgens are present in boys and girls, just in different amounts. Adrenal androgens rise in 10 y/o, causing girls' height spurt and underarm/pubic hair growth. Estrogens in girls' maturing ovaries contribute to height spurt by stimulating GH secretion and causing breasts, uterus, vagina to mature; body to take feminine proportions; and fat to build up. Boys' testes release androgen called testosterone which leads to muscle growth, body/facial hair, and other male characteristics. Androgens exert a GH-enhancing effect. Testes release some estrogen as well, leading to height spurt and temporary breast enlargement. Estrogens + androgens in both sexes stimulates gains in bone density
What factors other than adolescent brain's emotional/social network and cognitive-control network contribute to rise in risk-taking?
Temperament, parenting, SES, and neighborhood resources, which are linked to encouragement and opportunities to take risks
How does adolescents' capacity for executive function compare to that of adults?
fMRI evidence shows adolescents recruit prefrontal cortex's network of connections with other brain areas less effectively than adults do because prefrontal cognitive-control network takes time to fine-tune. Thus, teenagers' performance on executive function tasks requiring inhibition, planning, and future orientation is not yet fully mature
How do reactions to pubertal changes vary by gender and ethnicity?
African-American families compared to Caucasian-American families may better prepare girls for menarche, treating it as an important milestone and expressing less conflict over girls reaching sexual maturity. Thus, African-American girls react more favorably to puberty. Like girls, boys react to spermarche with mixed feelings. Boys know about ejaculation before but report no one spoke to them prior to/during puberty. Even boys educated in advance say they were unprepared. While almost all girls eventually tell a friend they're menstruating, far fewer boys tell anyone about spermarche. Overall, boys get much less social support than girls for changes in puberty and may benefit from opportunities to ask questions and discuss feelings with parent/professional
What is adrenarche?
An event when sex hormones begin to rise long before physical changes are visible (ages 6 to 8) when adrenal glands on top of each kidney start to release increased levels of adrenal androgens. Androgen levels increase by age 10, and some children experience their first feelings of sexual attraction
How does adolescents' brains' emotional/social network compare to that of adults?
As humans become sexually mature, neurons become more responsive to excitatory neurotransmitters, so adolescents respond more strongly to stressful events and experience pleasurable stimuli more intensely. Changes in emotional/social network also increase adolescents' sensitivity to social stimuli, making them highly reactive to peer evaluation. When peers are present, adolescents' brains are especially receptive to cues associated with risk taking
How prevalent are non-heterosexual orientations among US high school students?
As of 2011, 5% identify as gay, lesbian, or bisexual, and another 2-3% report being unsure of sexual orientation. An unknown number experience same-sex attraction but have not come out to friends or family
How can adolescence be socially described?
Contemporaries say, although eating disorders, depression, suicide and lawbreaking occur more than earlier, overall rate of psychological disturbance rises only slightly. Margaret Meade found Samoa's relaxed social relationships and openness to sexuality made adolescence pleasant (though successors found it was not as untroubled as Meade made it out to be)
What are changes in gross-motor performance during adolescence?
Girls have slow, gradual gains, leveling off by age 14 while boys show a dramatic spurt in strength, speed and endurance continuing to teen years. Gender gap in physical skill widens by age so that few girls perform as well as the average boy by middle adolescence. For boys, athletic competence is related to peer admiration and self-esteem. Many abuse performance-enhancing drugs like creatine and steroids. Although US government requires schools fund equal opportunities for males and females in all educational programs including athletics, girls fall short to some degree due to less encouragement and recognition for academic achievement. Generally, daily free-time physical activity declines with age 9-17 y/o, more for girls than boys. Only a few engage in regular exercise outside of school. Besides improving motor performance, sports and exercise influence cognitive and social development. Adolescents vary in enjoyment of sports and exercises
What changes in myelination does the brain undergo during adolescence?
Growth and myelination of stimulated neural fibers accelerate, strengthening connections across brain regions. In particular, linkages between two cerebral hemispheres through the corpus callosum, and between the prefrontal cortex and others areas in cerebral cortex and inner brain (i.e. amygdala), expand and attain rapid communication. As a result, prefrontal cortex becomes more effective in overseeing and managing integrated functioning of various areas, yielding more complex, flexible, and adaptive thought/behavior
What accounts for individual differences in pubertal growth?
Heredity influences timing. Nutrition and exercise make a difference (due to leptin protein, menarche occurs earlier for heavier girls). Culture, SES, and ethnicity play a role, as well as physical health. (menarche delayed in poverty-stricken regions with malnutrition and infectious disease) (menarche earlier for African-American girls than Caucasian girls). Emotional quality of childhood environments is also theorized. When child's safety and security is at risk, it is adaptive to reproduce early
What factors contribute to adolescent moodiness?
Higher pubertal hormone levels are linked to greater moodiness, but only modestly so. Several studies show negative moods were linked to a greater number of negative life events (e.g. difficulties with parents, disciplinary actions at school, breaking up with boy/girlfriend). Not only were negative life events more numerous in adolescence than childhood, but teenagers also reacted to them with greater emotion than children (heightened stress reactivity by changes in brain neurotransmitter activity)
What adaptive value does the strain on parent-child relationships during adolescence have?
In nonhuman primates, young typically leave the family group around the time of puberty. The same is true in many village and tribal cultures. Departure of young people discourages sexual relations between close blood relatives, but adolescents in industrialized nations, still economically dependent on parents, cannot leave the family. Thus, modern substitute of psychological distancing emerged
How did the longitudinal study of U.S. youths track changes in emotional/social network and cognitive-control network?
In teens 12 to 24, impulsivity (representing cognitive-control network) decreased steadily with age. However, sensation-seeking (representing emotional/social network) increased 12 to 16 and then had a more gradual decline through age 24
How do different societies formally recognize the onset of puberty?
Initiation ceremonies are used by many tribal and village societies to celebrate the onset of puberty. It is a ritualized announcement to the community, marking an important change in privilege and responsibility. This allows young people to know reaching puberty is a significant milestone in their culture. Unlike these societies, Western societies grant little formal recognition about this transition from childhood to adolescence. Some ceremonies like Jewish bar mitzvah and Hispanic quinceañera resemble initiation ceremonies but only within ethnic/religious subcultures, not marking meaningful change in social status in the large society. Instead, Western adolescents are granted partial adult status at many different status. Different ages are for starting employment, driving, voting, drinking, etc. while some contexts still regard them as children (home, school)
What characterizes body growth in adolescence?
It is striking. Boys have 4+ inches and 26 lbs per year while girls have 3.5 inches and 20 lbs. Cephalocaudal trend reverses; hands, legs, feet accelerate before torso. Large sex differences appear: boys' shoulders broaden relative to hips whereas girls' hips broaden relative to shoulders and waist. Boys end up larger than girls and have longer legs relative to rest of body since they have two extra years of preadolescent growth when legs grow fastest. Girls take on more fat than boys on arms, legs, and trunks 11-16 y/o while arm and leg fat decreases in adolescent boys. Although both sexes gain muscle, it's 150% greater or boys. Number of red blood cells increase in boys but not girls
How can adolescence be biologically described?
Jean-Jacques Rousseau the biological upheaval of puberty caused heightened emotionality, conflict and defiance of adults. G. Stanley Hall picked up this storm-and-stress perspective basing ideas off Darwin. He described it as a cascade of instinctual passions. Anna Freud expanded her father's theory viewing teen years as biologically based, universal "developmental disturbance". Genital stage is when sexual impulses reawaken, triggering psychological conflict and volatile behavior with the mature harmony from finding a partner as the end
How are reactions to pubertal changes time-dependent and culturally dependent?
Menarche was traumatic two generations ago, and today, girls commonly react with surprise due to sudden onset of event, otherwise reporting a mix of positive and negative emotions. Unlike 50-60 years ago, few girls in developed countries are uninformed, likely due to parents' greater willingness to discuss sexual matters and due to the spread of health education classes. Research in a variety of nations reveals large individual differences that depend on prior knowledge and support from family members, which in turn are influenced by cultural attitudes toward puberty and sexuality.
How does inadequate brain maturity impact frequency of risky behavior?
Most teens find it difficult to manage powerful feelings and impulses with a cognitive-control network not functioning optimally, contributing to their unchecked drive for novel experiences, like drug-taking, reckless driving, unprotected sex, and delinquent activity
How do parent-child relationships in adolescence differ by gender and progression in adolescence (age)?
Parent-daughter conflict tends to be more intense than conflict with sons maybe because girls reach puberty earlier and parents place more restrictions on girls. By late adolescence, only a small minority of families experience continuing friction. Adolescents display fewer angry behaviors while parents' angry responses declined steadily. Also, parents and teens increasingly used positive problem solving like compromise and reasoning
What are primary sexual characteristics?
Physical features involving reproductive organs directly: ovaries, uterus, vagina in females / penis, scrotum, testes in males. Development follows a standard sequence but varies in age
What are secondary sexual characteristics?
Physical features visible on the outside of the body and serve as additional signs of sexual maturity: breast development in females / appearance of underarm and pubic hair in both sexes. Development follows a standard sequence but varies in age
What is the general nature of parent-child relationships during adolescence?
Research in a diverse range of cultures show puberty is linked to a rise in intensity of parent-child conflict, which persists into middle adolescence. This may include keeping doors closed, resisting spending time with family, and becoming more argumentative. However, both teens and parents benefit from warm, protective family bonds throughout the lifespan. By the end of teen years, parent-adolescent interactions are less hierarchical, setting the stage for mutually supportive relationships in adulthood
What are the three phases of adolescence?
Researchers commonly divide adolescence into: 1) Early adolescence (11-12 to 14) period of rapid pubertal change 2) Middle adolescence (14 to 16) pubertal changes are now nearly complete 3) Late adolescence (16 to 18) young person achieves full adult appearance and anticipates assumption of adult roles
What is the growth spurt?
The first outward sign of puberty is this rapid gain in height and weight in girls at age 10 and boys age 12 1/2. Because estrogens trigger/restrain GH secretion more readily than androgens, girl is taller and heavier in early adolescence, but by age 13, she is surpassed by typical boys. Growth finishes in girls by age 16 and boys by age 17 1/2 when epiphyses at ends of long bones close completely
How do sleep cycles of teens now compare to those of generations before?
Today's teens with more evening social activities, part-time jobs, and bedrooms with screen media get much less sleep than teens of previous generations. They are also more likely to achieve less well in school, suffer from anxiety/irritability/depressed mood, and engage in high-risk behaviors
What changes do white and grey matter undergo during adolescence?
White matter (myelinated nerve fibers) increase, especially in the prefrontal cortex, the parietal lobes, and the corpus callosum. Grey matter (neurons, supportive material) declines, as unused synapses in cerebral cortex are pruned, especially the prefrontal cortex.
How do changes in mood differ between adolescents and adults?
Younger adolescents' moods (12 to 16) are less stable than those of older adolescents and adults. Their mood swings are strongly related to situational changes. Low points occurred in adult-structured settings - class, job, and religious services. High points of adolescents' days were times spent with friends and in self-chosen leisure activities and coincided with Friday and Saturday evenings, especially in high school. Going out with friends and romantic partners increases so much, it becomes a "cultural script" for what is supposed to happen, making teens who spend weekend evenings at home feel lonely
