CH 11 Summary

11.1 Brain Development and Physical Growth
The Brain
· There are two major brain growth spurts that occur during the teenage years.
· The first spurt occurs between 13 and 15 years of age. This spurt, for the most part, takes place in the parts of the brain that control spatial perception and motor functions, as well as executive processing. This makes mid-teens and adolescents abilities in these areas far exceed those of school age children.
· This first spurt enables teens to think abstractly and to reflect on their cognitive processes (Fischer & Rose, 1994).
· As evidence, researchers reveal major changes in brain organization show up within this spurt period.
· The second spurt begins around 17 years and continues into early adulthood (van der Molen & Molenaar, 1994). In this spurt the frontal lobes of the cerebral cortex are the focus of development (Davies & Rose, 1999). This area of the brain controls logic and planning. This is why older teens differ from younger teens in terms of how they deal with problems that require these cognitive functions.

The Body
· An adolescent may grow 3 to 6 inches per year for several years. After this growth spurt teenagers add height and weight slowly until they reach their adult size.
· Girls attain most of their height by age 16, boys continue to grow until 18-20 years.
· Teenagers' hands and feet are first to grow to full adult size, followed by the arms and legs and finally the truck. This is why teenagers are often stereotyped as awkward or uncoordinated.
· Joint development enables adolescents to achieve coordination levels near those of adults.
· Boys continue to lag behind girls, enabling early-adolescent girls to outperform boys of the same age on a variety of athletic skills, like pitching softball.
· Around age 17-18 boys catch up to girls, and on average gain superiority in coordinated movement.
· Muscle fibers also become thicker and denser making adolescents much stronger in just a few years. This increase in strength occurs in both boys and girls, but is more prevalent in boys. Among adult men, 40% of the total body mass is muscle, as apposed to 24% in adult women.
· Prior to the age of 12, physical endurance levels are similar in boys and girls. In the teenage years the heart and lungs increase considerably in size and the heart rate drops. This is more marked in boys,and enables them to exceed the endurance levels of girls.

11.2 Milestones in Puberty
· The change that most associate with adolescence growth and development is sexual maturity.
· Puberty is the collective term for all of the changes, seen and unseen, that are needed for reproductive maturity.
· Adrenarch is when the pituitary gland, which controls all other glands, tells the adrenal gland to increase production of androgen. This is when puberty begins and occurs around the age of 7 or 8.
· Next, the pituitary gland begins secreting hormones that stimulate the growth of ovaries in girls and testes in boys. As they grow, these glands secrete hormones, testosterone in boys and estradiol in girls, that cause the sex organs to develop.
· The pituitary gland also secrets the thyroid stimulating hormone and general growth hormone. These,along with adrenal androgen, interact with the specific sex hormone and affect growth.
· Adrenal androgen, which is similar to testosterone, plays an important role for girls, triggering the growth spurt and affecting the development of pubic hair. Adrenal androgen is less significant for boys, probably because of the testosterone boys already have so much of.
· These hormonal changes trigger the development of sex organs and a much broader set of changes in the brain, bones, muscles, and other body organs.
· Most obvious changes of puberty are associated with sexual maturity. Changes in primary sex characteristics include growth of the testes and penis in the male, and ovaries, uterus and vagina in the female. Changes in secondary sex changes include breast development in girls and voice pitch and beard growth in boys and body hair growth in both sexes.
Sexual Development in Girls
· The first steps of sexual development in girls are early changes in breast and pubic hair, closely followed by a peak growth spurt and the development of breasts and pubic hair, then menarche, which typically occurs 2 years after the other visible change begin. Menarche is only succeeded by the final stages of breast and pubic hair development.
· In the US today, only 10% experience menarche before age 11, and more that 90% have reached menarche by age 14. (Chumlea, Schubert, Kulin, Himes & Sun, 2003)
· While it is possible to get pregnant shortly after menarche, as many as 3/4 of the cycles in the first year and 1/2 of the cycles in the second year, the female produces no ovum. (Adelman & Ellen, 2002)
· This contributes to the assumption that young teenaged girls cannot get pregnant.
The Secualr Trend
· The timing of menarche has changed drastically between mid-19th and mid-20th centuries.The average age of menarche in 1840 was 17 and has dropped steadily until the 1950's at a rate of about 4 months per decade, an example of a secular trend.
· This change was likely caused by significant changes in diet and lifestyle, particularly increases in protein and fat intake.
· Data collected over shorter periods of time support the nutritional explanation. One study showed the age of menarche can plummet from 16 to 13 within just a few years after nutritional improvements are experienced (Khanna & Kapoor, 2004)
· Some exaggerated media accounts would have us believe that girls may someday attain sexual maturity during infancy (Viner, 2002), however, there is strong evidence for a genetic age range for when menarche can occur.
· The average age of menarche for Caucasian females in the US is 12.6-12.8 yrs and has not changed since the mid 1940's. (Kaplowitz & Oberfield, 1999; Rosenfield, Lipton and Drum, 2009; Viner, 2002). The average age for African American girls is 12.1 yrs, and for Hispanic girls the average age is 12.3 yrs, both of which represent a drop of about 2 months since the mid 1960's (Kaplowitz & Oberfield, 1999; Rosenfield, Lipton and Drum, 2009)
· In contrast to the stability of menarche, the age girls show secondary sex characteristics, the appearance of breast buds and pubic hair, have dropped significantly in recent decade (Rosenfield, Lipton and Drum, 2009). On average, girls show these signs earlier than their mothers or grandmothers increasing the time between appearance of secondary sex characteristics and menarche (Parent et al., 2009). Researchers link this to childhood obesity.
· The appearance of breasts and pubic hair continues to be extremely rare in girls younger than 8, less than 1%. A girl younger than 8 that does display these signs may be diagnosed with precocious puberty, a diagnoses that requires follow-up to determine whether a tumor, hormonal disorder or other disease or condition is responsible (Jospe,2011)
· Obesity is a cause and consequence for early development of secondary sex characteristics.
· Little is known about these affects and health later in life.
Sexual Development in Boys
· Boys' first ejaculation or spermarche occurs between 13 and 14 yrs of age, however, the production of viable sperm does not happen until a few months after the first ejaculation.
· Most boys do not attain adult levels of sperm until stage 5, the stage where the voice drops and facial hair develops.
· The secular trend is far less dramatic among boys.
· some studies suggest obesity delays puberty in males, other research says that it speeds up puberty just like in girls.
11.3 Timing of Puberty
· Researchers think that heredity and behavioral factors may contribute to hormonal secretions in the body, therefore controlling the age of puberty.
· Discrepancies between expectation and what actually occurs in puberty determine the physiological effect of puberty. If puberty occurs outside of the desired or expected range, one may think less of themselves, be less happy with their bodies and the process of puberty.
· They may also show other signs of psychological distress.
· Early developing girls tend to have more negative body images, are more likely to get into trouble at school and home,become sexually active and become depressed.
· Among boys, very early and very late puberty are associated with depression. However research shows that males slightly ahead of their peers in pubertal development often occupy leadership roles and are more successful in adulthood.
· Substance abuse is associated with early puberty.
· The family context in which early puberty occurs, can either diminish or intensify its effects on adolescents.
· Parenting moderates the effects of pubertal timing such that both early-maturing boys and girls are more likely to become involved in sexual activity and substance abuse if their parents are permissive.
· Children that live in low risk households, those with adequate material resources, stable intimate relationships, are not involved in substance abuse and have good relationships with their children, are less likely to exhibit the negative effects of early puberty than their high risk peers.
· Peer contexts also affect how pubertal timing affects adolescents.
11.4 Sexual Behavior
· First sexual encounters typically occur in the mid to late teens, although how often and with how many partners vary widely.
Prevalence of Sexual Behavior
· The proportion of sexually experienced teens increases from grades 9 to 12 and boys are found to be more sexually active than girls.
· In the past 3 decades, rates of sexual activity among teens has dropped significantly. In 1988, 60% of males and 51% of females ages 15 to 19 reported having sex at least once. In 2008, the rates were 43% and 42%.
· Sexual activity varies somewhat across racial groups.
· African American teens are more likely to have their first sexual encounter before the age of 13.
· Those who begin sexual activity early are more likely to live in poor neighborhoods in which young people are not monitored by adults. They come from poorer families or from families in which sexual activity is condoned and dating rules are lax.
· Adolescents' moral beliefs and the activities in which they participate predict their sexual activity.
· Alcohol use is associated with 22% of adolescent sexual encounters.
Contraceptive use
· About 90% of high school students stated they learned about STD's in school. Even with this knowledge, many teens lack the assertiveness to resist sexual pressure or discuss condom use.
· Condom use has increased among teens from 31% of females and 53% in 1988 to 53% for females and 79% for males in 2008.
· Fewer teens today use oral contraceptives than their counterparts in earlier decades. Just over 30% for females ages 15-19 reported being on the pill in 2008, compared to the 42% in 1988.
· These statistics are why public health advocates and developmentalists say more effective sex ed programs are needed.
· Many adults object to sex ed because they feel it will cause teenagers that are not sexually active to become so.
· Studies show that abstinence based programs are more effective in younger students that are not yet sexually active to delay first encounter sexual experiences.
· Students who participate in multi session programs are more likely to remain abstinent than those exposed to single session presentations.
· Sex education advocates suggest that abstinence and contraceptive education should not be taught in either/ or terms, but to be taught together so that it may delay sexual encounters and encourage contraception use when they decide to become sexually active.
11.5 Adolescent Pregnancy
· The rate of teen pregnancy is higher in the US than in any other industrialized country.
· The annual pregnancy rate is less than 1 per 1,000 for girls younger than 15; 22 per 1,000 for girls ages 15-17; and 70 per 1,000 for 18-19 year olds (Martin et al., 2010).
· While birthrates have dropped among teen mothers since the 1960's, the birthrate to unmarried teens has risen. During the 1960's 80% of teens that gave birth were married, in 2003, only 14% were married (Martin et al., 2010).
· The proportion of teenage mothers that eventually marry the baby's father has also declined and again there are ethnic differences. < 5% of African American teen mothers marry their child's father, compared to 26% of Hispanics and 41% of Caucasians. Furthermore, only 17% of teen moms maintain romantic relationships with the father beyond the first few months after birth.
· Whether a girl becomes pregnant in her teen years depends on the same factors that predict sexual activity in general.
11.6 Sexual Minority Youth
· Physical attraction to members of the opposite sex,or heterosexuality is one of the defining features of adolescents for the great majority of teenagers. For some, it is a time when they discover or confirm that they are attracted to members of the same sex, or homosexuality or both sexes, bisexuality. Still others become increasingly convinced that their psychological gender is inconsistent with their biological sex, transgenderism.
Gay, Lesbian, and Bisexual Adolescents
· 92% of teens indentify as being heterosexual, about 7% of teens are unsure, and 1% classify themselves as being exclusively gay, lesbian or bisexual. By adulthood, 94 % report being heterosexual and 5% report being gay, lesbian or bisexual, leaving just 1% that is still unsure.
· Family studies suggest that homosexuality runs in families. Families of most gay men have a higher proportion of homosexual males than families of heterosexual men.
· Such findings strengthen the hypothesis that homosexuality has a biological basis, this does not mean that environment plays no role in homosexuality. For example, one identical twin is homosexual, the other is not homosexual 40-50% of the time.
· The process through which an individual comes to realize he or she is homosexual tends to be a gradual one. Some researchers think the process begins in middle childhood as a feeling of doubt about ones heterosexuality.
· Many gay men and lesbian women recall having had homosexual fantasies during their teen years, but the final steps toward self awareness take place in early adulthood.
· Many homosexual teens report feeling isolated from and unaccepted by their peers. They are also more likely to report being bullied by peers than heterosexual adolescents are. This may help explain rates of depression, attempted suicide and substance abuse in homosexual and questioning teens.
Transgendered Teens
· Transgendered adolescents usually report that in early childhood, they were more interested in activities that are associated with the opposite sex.
· Most children that are attracted to cross gender activities, do not exhibit transgenderism after puberty.
· Denial and anger expressed by family members once one has "come out" apmlifies these teens' distress. As a result, gay, lesbian, bisexual and transgendered are at higher risk of suicide.
· Once one has accepted their transgendered status, the may choose to live as the opposite sex on a full time basis, known as transsexualism. Some are content with just being, some sex sexual reassignment surgery. At least 1/2 of those that initially wanted the sexual reassignment surgery eventually reject it.
11.7 Sensation Seeking
· Teenagers appear to have a higher level of sensation seeking, or a desire to experience increased levels of arousal such as those that accompany fast driving or the "high" associated with drugs.
· Risky behaviors may be more common in adolescents than any other period because they help teenagers gain peer acceptance and establish autonomy with respect to parents and other authority figures.
· Students involved in extra curricular activities are less likely value popularity and less likely to engage in risky behavior.
· Sex, violence, drug and alcohol abuse in the media may influence teens' risky behaviors. Teens who are highest in sensation seeking are those that will be the most strongly influenced.