week 2 puberty, health & biological foundations

8/10/2019 Week 2 Puberty, Health & Biological Foundations

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WEEK 3


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Puberty

The period of rapid physical maturation involving

hormonal and bodily changes that takes place primarily in

early adolescence

While puberty is thought of as the most important markerfor the beginning of adolescence, for virtually everyone,

puberty ends long before adolescence is exited


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Determinants of Puberty

We do not know precisely what initiates puberty, a

number of complex factors are involved:

Changes in the endocrine system

Weight

Body fat

Leptin


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Determinants of Puberty

We do not know if these complex factors are a cause or a

consequence of puberty (Susman & Dorn, 2009)

There is increased interest in the role that birth weight,

rapid weight gain in infancy, obesity, and socioculturalfactors might play in pubertal onset and characteristics


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Heredity

Puberty is not an environmental accident

Programmed into the genes of every human being is thetiming for the emergence of puberty (Mueller & others,2010)

Recently, scientists have begun to conduct moleculargenetic studies in an attempt to identify specific genesthat are linked to the onset and progression of puberty (He& others, 2010; Paris & others, 2010)


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Heredity

Puberty takes place between about 9 and 16 years of agefor most individuals

Environmental factors can also influence its onset andduration (Belsky & others, 2010)


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Hormones

Hormones: Powerful chemical substances secreted by the

endocrine glands and carried throughout the body by the

bloodstream (Divall & Radovick, 2008)

Androgens: The main class of male sex

hormones

Estrogens: The main class of female sex

hormones


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Hormones

Testosteroneis an androgen

Plays an important role in male pubertal development

Rising testosterone levels are associated with a number ofphysical changes in boys:

Development of external genitals

Increase in height

Voice changes (Campbell & Mbizo, 2006; Goji & others, 2009)

Also linked to sexual desire and activity (Cameron, 2004)


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Hormones

Estradiolis an estrogen

Plays an important role in female pubertal development

As estradiol levels rise changes in girls occur:

Breast development

Uterine development

Skeletal changes

The identity of hormones that contribute to sexual desireand activity in adolescents is less clear for girls than it is for

boys (Cameron, 2004)


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The Endocrine System

Puberty onset involves the activation of thehypothalamic-pituitary-gonadal (HPG) axis

Hypothalamus

Structure in the higher portion of the brain that monitors eating,drinking and sex

Pituitary gland

The endocrine gland that regulates other glands and secretes FSHand LH

Thyroid gland

Interacts with the pituitary gland to influence growth and skeletalmaturation

Gonads

The sex glandstestes in males, ovaries in females that secretesex hormones


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Figure 2.2 - The Major Endocrine Glands Involved in

Pubertal Change


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Figure 2.3 - The Feedback System of Sex Hormones

LH-RF (luteinizing hormone-releasingfactor) and FSH-RF (follicle- stimulatinghormone-releasing factor) stimulate

pituitary gland

LH (luteinizing hormone) and FSH(follicle- stimulating hormone)stimulate gonads

Gonads: testes in males, ovaries infemales


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Adrenarche and Gonadarche

Adrenarche involves hormonal changes in the adrenal

glands

These changes occur surprisingly early, from about 6 to 9

years of age in girls and about one year later in boys beforewhat is generally considered the beginning of puberty

(Dorn & others, 2006)

During adrenarche and continuing through puberty, the

adrenal glands secrete adrenal androgens, such asdehydroepiandrosterone (DHEA) (Miller, 2008)


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Gonadarche

Follows adrenarche by about two years; is the period most

people think of as puberty

Involves the maturation of: Primary sexual characteristics: Ovaries in females, testes in males

Secondary sexual characteristics: Pubic hair, breast, and genital

development (Dorn & others, 2006)

The hallmark of gonadarche is reactivation of the hypothalamic-pituitary-gonadal axis (HPG). . . . The initial activation of the HPG axis

was during the fetal and neonatal period (Dorn & others, 2006, p. 35)


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In the United States, the gonadarche period begins atapproximately 9 to 10 years of age in non-Latina white girls,

and 8 to 9 years in African American girls (Herman-Giddens,

Kaplowitz, & Wasserman, 2004)

In boys, gonadarche begins at about 10 to 11 years of age


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Menarche

The first menstrual period

Occurs in mid- to late-gonadarche in girls

Spermarche The first ejaculation of semen

Occurs in early- to mid-gonadarche in boys


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Weight, Body Fat, and Leptin

Higher weight, especially obesity, is linked to earlierpubertal development (Kaplowitz, 2009) A body weight of 106 +/- 3 pounds may trigger menarche and

the end of the pubertal growth spurt (Friesch, 1984)

This specific weight target is not well documented (Susman,2001)

Other scientists have hypothesized that the onset ofmenarche is influenced by the percentage of body fat inrelation to total body weight

A minimum of 17 percent of a girls body weight must becomprised of body fat

As with the weight target, this percentage has not beenconsistently verified


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Weight, Body Fat, and Leptin

In boys undernutrition may delay puberty (Susman, Dorn, andSchiefelbein, 2003)

The hormone leptin may signal the beginning and progressionof puberty


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Weight at Birth and in Infancy

There is increasing evidence for a link between pubertys

onset and characteristics and birth weight and weight gain

during infancy (Ong, 2010)

Low birth-weight girls experience menarche approximately5 to 10 months earlier than normal birth-weight girls

Low birth-weight boys are at risk for small testicular

volume during adolescence (Ibanez & de Zegher, 2006)


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Sociocultural and Environmental Factors

Recent research indicates that cultural variations and

early experiences may be related to earlier pubertal onset

Adolescents in developed countries and large urban areas

reach puberty earlier than their counterparts in less

developed countries and rural areas (Graham, 2005)

Children who have been adopted from developing countries

to developed countries often enter puberty earlier than their

counterparts who continue to live in developing countries(Teilmann & others, 2002)


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Sociocultural and Environmental Factors

African American females enter puberty earlier than Latina

and non-Latina females, and African American males enter

puberty earlier than non-Latino males (Biro & others, 2006;

Talpade, 2008)

Early experiences that are linked to earlier pubertal onset

include adoption, father absence, low socioeconomic

status, family conflict, maternal harshness, and child

maltreatment (Arim & others, 2011; Deardorff & others,

2011; Ellis & others, 2011)


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Growth Spurt

The later growth spurt of boys produces a greater leg

length in boys than in girls

Boys facial structure becomes more angular during

puberty, whereas girls facial structure becomes rounder

and softer


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Figure 2.4 - Pubertal Growth Spurt


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Sexual Maturation

Male pubertal characteristics develop in this order:

Increased penis and testicle size

Appearance of straight pubic hair

Minor voice change

First ejaculation (spermarche)

Appearance of kinky pubic hair

Onset of maximum growth

Growth of armpit hair

More detectable voice changes

Growth of facial hair


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Sexual Maturation

Female pubertal characteristics develop in this order:

Breast development

Growth of pubic hair

Growth of armpit hair

Height gain

Hips become wider than shoulders

First menstruation (menarche)

No voice changes occur that are comparable to those in

pubertal males


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Sexual Maturation

There may be wide individual variations in the onset and

progression of puberty

Precocious puberty: The very early onset and rapid

progression of puberty Characteristics of precocious puberty (Blakemore & others,

2009, p. 58):

Pubertal onset that occurs before the age of 8 in girls and before the age

of 9 in boys (Dorn & Biro, 2011)

Occurs approximately 10 times more often in girls than in boys

Treated by medically suppressing gonadotropic secretions, which

temporarily stops pubertal change (Kaplowitz, 2009)


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Secular Trend

Recent analyses call into question blanket statements that

puberty has continued to rise in recent years

A panel of experts recently examined pubertal timing data and

agreed that breast development and menarche occurred earlier

in girls from 1940 to 1994 but that current data are insufficient

to conclude that earlier pubertal development took place for

boys across this time frame (Euling & others, 2008)

A recent research review concluded that puberty does seem to

be occurring only in overweight girls but that obesity delays

puberty onset in boys (Walvoord, 2010)


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Psychological Dimensions of Puberty

Body image Adolescents are preoccupied with their bodies (Lawler &

Nixon, 2010; Markey, 2010)

Gender differences

In general, throughout puberty girls are less happy with their bodiesand have more negative body images than boys (Crespo & others,2010)

As pubertal change proceeds, girls often become more dissatisfied withtheir bodies, probably because their body fat increases (Markey, 2010;Yuan, 2010)

In contrast, boys become more satisfied as they move through puberty,probably because their muscle mass increases


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Hormones and behavior

Hormonal factors are thought to account for at least part of theincrease in negative and variable emotions that characterizeadolescents (Vermeersch & others, 2008)

In boys, higher levels of androgens are associated with violence andacting-out problems (Van Goozen & others, 1998)

There is also some indication that increased estrogen levels are linkedto depression in adolescent girls (Blakemore, Berenbaum, & Liben,2009)


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Hormonal factors alone are not responsible for adolescentbehavior

Hormonal activity is influenced by many environmental factors,including parent-adolescent relationships, stress, eating patterns,sexual activity, and depression can activate or suppress various aspects

of the hormone system (DeRose & Brooks-Gunn, 2008)


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Early and late maturation When adolescents mature earlier or later than their peers, they

often perceive themselves differently (de Rose & others, 2011;Graber, Nichols, & Brooks-Gunn, 2010; Negriff, Susman, &Trickett, 2011)

The Berkeley Longitudinal Study found that early-maturing boysperceived themselves more positively and had more successful peerrelations than did late-maturing boys.

The findings for early-maturing girls were similar but not as strong as forboys (Jones, 1965)

An increasing number of researchers have found that earlymaturation increases girls vulnerability to a number of

problems (de Rose & others, 2011; Graber, Nichols, &Brooks-Gunn, 2010; Negriff, Susman, & Trickett, 2011)


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Health

Adolescence: A critical juncture in health Adolescence is a critical juncture in the adoption of behaviors

that are relevant to health (Fatusi & Hindin, 2010)

Many of the behaviors that are linked to poor health habits and

early death in adults begin during adolescence Why might adolescents develop poor health habits?

In adolescence, many individuals reach a level of health, strength, andenergy that they will never match during the remainder of their lives

They also have a sense of uniqueness and invulnerability that convincesthem that they will never suffer from poor health, or if they do, they willquickly recover


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Health

Increasingly, experts recognize that whether or not adolescentsdevelop health problems depends primarily on their behavior(Turbin & others, 2006)

Experts goals are to:

Reduce adolescents health-compromising behaviors, such asdrug abuse, violence, unprotected sexual intercourse, anddangerous driving

Increase adolescents health-enhancing behaviors, such as

exercising, eating nutritiously, wearing seat belts, and gettingadequate sleep


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Risk-Taking Behavior

One type of health-compromising behavior that increases inadolescence is risk taking (Lynn-Lansman & others, 2010;

Rao & others, 2010)

Beginning in early adolescence, individuals seek experiences

that create high intensity feelings . . . adolescents like intensity,

excitement, and arousal

While these patterns of emotional changes are evident to some degree

in most adolescents, it is important to acknowledge the wide range of

individual differences during this period of development (Dahl, 2004, p.6)


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Risk-Taking Behavior

Researchers also have found that the more resources there

are in the community, such as youth activities and adults

as role models, the less likely adolescents are to engage in

risky behavior (Jessor, 1998; Yancey & others, 2010) Recently, neurobiological explanations of adolescent risk-

taking have been proposed (Steinberg, 2009)


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Health Services

Adolescents underutilize other health-care systems (Hoover &others, 2010)

Many adolescents dont believe that health-care providers canhelp them

Some health-care providers may want to provide better healthcare for adolescents but lack adequate training and/or timeduring their visit

Of special concern is the low use of health services by older

adolescent males


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Health Services

Among the chief barriers to better health care for adolescentsare cost, poor organization and availability of health services,lack of confidentiality, and reluctance on the part of healthcare providers to communicate with adolescents about

sensitive health issues. (Hoover & others, 2010; Lara-Torre,2008)


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Leading Causes of Death

The three leading causes of death in adolescence andemerging adults are unintentional injuries, homicide,and suicide (National Vital Statistics Reports, 2010)

Unintentional injuries

Almost half of all deaths from 15 to 24 years of age are due tounintentional injuries, approximately of them involvingmotor vehicle accidents

In about 50% of motor vehicle fatalities involving adolescents,the driver has a blood alcohol level of 0.10%twice the levelneeded to be designated as under the influence in somestates


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Emerging Adults Health

The negative effects of abusing ones body might now showup in emerging adulthood, but they probably will surfacelater in early adulthood or in middle adulthood (Rathunde &Csikszentmihalyi, 2006)


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Nutrition

Schools also can play an important role in adolescents

eating patterns

A special concern in American culture is the amount of fat in

the diet


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Exercise

Researchers have found that individuals become less activeas they reach and progress through adolescence (Pate &others, 2009)

A recent national study of U.S. 9- to 15-year-olds revealed that

almost all 9- and 11-year-olds met the federal governmentsmoderate to vigorous exercise recommendations per day (aminimum of 60 minutes a day), but only 31 percent of 15-year-olds met the recommendations on weekdays and only 17

percent met the recommendations on weekends (Nadar &

others, 2008)


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Exercise

Ethnic differences in exercise participation rates of U.S.adolescents also occur and these rates vary by gender

A comparison of adolescents in 28 countries found that U.S.

adolescents exercised less and ate more junk food than

adolescents in most of the other countries (World Health

Organization, 2000)

U.S. adolescents were more likely to eat fried food and less

likely to eat fruits and vegetables than adolescents in most

other countries studied


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Exercise

Exercise is linked to a number of positive outcomes inadolescence (Sund, Larsson, & Wichstrom, 2010)

The benefits of regular exercise include:

A positive effect on weight status (McMurray & others, 2008)

Reduced triglyceride levels, lower blood pressure, a lower

incidence of type II diabetes, and cardiovascular disease

(Butcher & others, 2008; Lobelo & others, 2010)

Physical fitness in adulthood (Mikkelsson & others, 2006)


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Exercise

Higher level of task preparation and response inhibition, whichbenefit learning and academic achievement (Stroth & others,

2009)

Lower drug use (Delisle & others, 2010)

Positive sleep patterns (Brand & others, 2010)

A possible buffer against the stress and improvement in mental

health and life satisfaction (Butcher & others, 2008)

Improvement in cognitive skills (Best, 2011)


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Roles of Families, Schools, and TV/Computers in Adolescent

Exercise

Families

Parents play an important role in influencing adolescents

exercise patterns (Dugan, 2008)

A recent study revealed that 9- to 13-year-olds were more

likely to engage in physical activity during their free time

when the children felt safe, had a number of places to be

active, and had parents who participated in physical activities

with them (Heitzler & others, 2006)


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Exercise

Schools Some of the blame for the poor physical condition of U.S.

children and adolescents falls on U.S. schools, many of which

fail to provide physical education class on a daily basis (Pate

& others, 2010; Schmottiach & McManama, 2010) A recent national survey revealed that only 30% of U.S. 9ththrough 12th

graders participated in PE classes 5 days in an average school week

(Eaton & others, 2008)


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Exercise

Males (33%) were more likely to participate at this level than females(27%)

Tenth graders were most likely to regularly take a PE class (47%); 11th

(30%), and 12thgraders (31%)

Other research studies have found positive benefits for

programs designed to improve the physical fitness of students

(Timperio, Salmon, & Ball, 2004; Veugelers & Fitzgerald,

2005)


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Sports

Sports can have both positive and negative influences onadolescent development (Adie, Dude, & Ntoumanis,2010; Busseri & others, 2010)

Potential positive influences

Many sports activities can improve adolescents physicalhealth and well-being, self-confidence, motivation to excel,and ability to work with others (Gaudreau & others, 2009)

Adolescents who participated in sports were less likely to

engage in such risk-taking behaviors as truancy, cigarettesmoking, sexual intercourse, and delinquency (Nelson &Gordon-Larsen, 2006)


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Sports

Potential negative influences:

Pressure to achieve and win, physical injuries, distraction

from academic work, and unrealistic expectations for success

as an athlete (Metzl, 2008)

Pressure by parents and coaches to win at all costs,competition anxiety, and self-centeredness (Smith & Smoll,

1997)

Injuries (Halstead & others, 2010; Stein & Micheli, 2010)

Use of performance-enhancing drugs, such as steroids (Elliot

& others, 2007)


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Sports

Coaches who create a performance-oriented motivationalclimate that is focused on winning, public recognition, and

performance relative to others (Roberts, Treasure, &

Kavussanu, 1997)

The female athlete triad: disordered eating, amenorrhea, &osteoporosis (Misra, 2008; Patano, 2009)


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Sleep

There has been a surge of interest in adolescent sleep patterns(Abe, Hagihara, & Nobutomo, 2010; Fakier & Wild, 2010;McHale & others, 2010)

In a survey conducted by the National Sleep Foundation

(2006): 45% of the adolescents got inadequate sleep on school nights

(less than eight hours)

Adolescents who got inadequate sleep on school nights were

more likely to feel more tired or sleepy, more cranky andirritable, fall asleep in school, be in a depressed mood, and drankcaffeinated beverages than their counterparts who got optimalsleep


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Sleep

Mary Carskadon and her colleagues have conducted a numberof research studies on adolescent sleep patterns

They found that when given the opportunity adolescents willsleep an average of 9 hours and 25 minutes a night. Most get

considerably less than 9 hours of sleep, especially during theweek

Carskadon has suggested that early school starting times maycause grogginess, inattention in class, and poor performance ontests

Research indicates that sleep patterns change in emergingadulthood (Kloss & others, 2011; Wolfson, 2010; Galambos,Howard, & Maggs, 2011)

Evo ution, Here ity, an


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Evo ution, Here ity, anEnvironment

The evolutionary perspective

In terms of evolutionary time, humans are relative

newcomers to the earth

As our earliest ancestors left the forest to feed on thesavannahs, and finally to form hunting societies on the open

plains, their minds and behaviors changed



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Evo ution, Here ity, anEnvironment

Natural selection:The evolutionary process that favorsthose individuals of a species who are best adapted tosurvive and reproduce

Charles Darwins On the Origin of Species (1859)

Adaptive behavior: A modification of behavior thatpromotes an organisms survival in the natural habitat

All organisms must adapt to particular places, climates, foodsources, and ways of life in order to survive



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vo ution, Here ity, anEnvironment

Evolutionary psychology

Emphasizes the importance of adaptation, reproduction, and

survival of the fittest in explaining behavior

The process of natural selection favors those behaviors that increase

organisms reproductive success and their ability to pass their geneson to the next generation (Enger, Ross, & Bailey, 2009)

Evolutionary developmental psychology

There is growing interest in using the concepts of evolutionary

psychology to understand human development (Buss, 2011; Greve

& Bjorklund, 2009; Hawley, 2011)



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, y,Environment

Evaluating evolutionary psychology

Albert Bandura (1998) has criticized the biologizing of

psychology

He rejects what he calls one-sided evolutionism

Evolution gave humans body structures and biological potentialities, not

behavioral dictates

Stephen Jay Gould (1981) concluded, in most domains, human

biology allows a broad range of cultural possibilities


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The Genetic Process

Our many traits and characteristics that are geneticallyinfluenced have a long evolutionary history that is retained

in our DNA

The nucleus of each human cell contains chromosomes

threadlike structures that contain DNA

DNA: A complex molecule that contains genetic information

Genes: Short segments of DNA which direct cells to

reproduce themselves and to assemble proteins


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Figure 2.13 - Cells, Chromosomes, Genes, and DNA


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The Genetic Process

The number of human genes has been revised furtherdownward to approximately 21,500 (Ensembl Human,

2008)

Each segment of DNA is not translated, in automation-like

fashion, into one and only protein


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The Genetic Process

Rather than being an independent source of information,DNA collaborates with other sources of information to

specify our characteristics (Diamond, 2009; Diamond,

Casey, & Munakata, 2011)

In short, a single gene is rarely the source of a proteinsgenetic information, much less of an inherited trait

(Gottlieb, 2007)


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Here ity-Environment


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yInteraction

Heredity and environment interact to produce development

Behavior genetics: The field that seeks to discover the

influence of heredity and environment on individual

differences in human traits and development (Goldsmith,

2011; Gregory, Ball, & Button, 2011)

To study the influence of heredity on behavior, behavior

geneticists use twin and adoption studies

Identical twins are monozygotic twins

Fraternal twins are dizygotic twins

Here ity-Environment


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yCorrelations

An individuals genes influence the types of environments towhich they are exposed

Three ways that heredity and environment are correlated(Scarr, 1993):

Passive genotype-environment correlations

Evocative genotype-environment correlations

Active (niche-picking) genotype-environment correlations

Scarr concludes that the relative influence of the threegenotype-environment correlations changes as childrendevelop from infancy through adolescence


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Figure 2.14 - Exploring Heredity-Environment Correlations


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Shared and Non-Shared Environmental Experiences

Behavior geneticists emphasize that another way ofanalyzing the environments role in heredity-environment

interaction is to consider experiences that adolescents share

in common with other adolescents living in the same home,

as well as experiences that are not shared (Plomin & others,2009)

Behavior geneticist Robert Plomin (2004) has found that

common rearing, or shared environment, accounts for little of

the variation in adolescents personality or interests


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The Epigenetic View

The heredity-environment correlation view

emphasizes how heredity directs the kind of

environmental experiences individuals have

In line with the concept of the collaborative gene, theepigenetic view emphasizes that development is the

result of an ongoing, bidirectional interchange

between heredity and the environment (Diamond,

2009; Gottlieb, 2007)


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Gene x Environment GxE


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Interaction

An increasing number of studies are exploring howthe interaction between heredity and environment

influences development, including interactions that

involve specific DNA sequences (Caspi & others,

2011; Rutter & Dodge, 2011)

This type of research describes GxE interaction: the

interaction of a specific measured variation in DNA

and a specific measured aspect of the environment(Diamond, 2009; Dodge & Rutter, 2011)


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Conclusions About Heredity-Environment Interaction

Heredity and environment operate together The relative contributions of heredity and environment are not

additive

Nor is it accurate to say that full genetic expression happens

once, around conception or birth Genes produce proteins throughout the life span, in many different

environments

The emerging view is that many complex behaviors likely

have some genetic loading gives people a propensity for aspecific developmental trajectory (Goldsmith, 2011; Plomin

& others, 2009)

week 2 puberty, health & biological foundations

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