chapter 13

Chapter 13: Adolescence – Physical Development

Chapter Objectives

  • After this chapter, students should be able to:

    • Explain the changes in physical growth and brain growth.

    • Compare and contrast different male and female changes that occur during puberty.

    • Discuss teenage pregnancy, birth control, and sexual health.

    • Summarize adolescent health: sleep, diet, and exercise.

    • Discuss drug and substance abuse.

    • Explain the prevalence, risk factors, and consequences of adolescent pregnancy and sexual health.

    • Describe several mental health issues for teens.

Introduction

  • Adolescence is the developmental period that begins with puberty and ends with the transition to adulthood.

    • The commonly accepted starting age for adolescence is age 12.

    • Defining the end of adolescence is more complex and can vary widely between individuals.

    • Historically, the duration of adolescence has evolved, with evidence suggesting it is lengthening:

    • Individuals now begin puberty earlier and transition into adulthood later compared to the past.

    • Average Onset of Puberty:

      • Girls: Ages 10–11.

      • Boys: Ages 11–12.

    • Since the 19th century, the average onset age has decreased by approximately 3–4 months per decade.

    • Factors attributed to this decrease include better nutrition, obesity, increased father absence, and environmental influences (Steinberg, 2013).

    • Social milestones such as completing education, achieving financial independence, getting married, and becoming a parent are now happening later than in previous generations.

Physical Growth

  • Adolescent Growth Spurt:

    • Defined as a rapid increase in height and weight during puberty due to the simultaneous release of:

    • Growth hormones,

    • Thyroid hormones,

    • Androgens.

    • Males generally experience their growth spurts approximately two years later than females.

  • Growth patterns:

    • Growth occurs non-uniformly, where different body parts grow at different rates which may cause an adolescent body to appear out of proportion.

    • Growth order:

      • Extremities (head, hands, feet) grow first,

      • Followed by arms and legs,

      • Then the torso and shoulders.

    • During puberty, bone density increases, making bones harder but also more brittle.

  • Sex Differences in Growth:

    • Before puberty, males and females exhibit similar distributions of fat and muscle.

    • During puberty:

    • Males gain muscle mass more rapidly than females.

    • Females experience a higher increase in body fat.

    • Heart and lung size and capacity increase, influencing exercise strength and tolerance.

Brain Growth

  • Brain development continues into the early 20s, with significant growth in the frontal lobe.

    • The frontal lobe is crucial for judgment, impulse control, and planning.

    • Changes associated with puberty:

    • Increased risk-taking and heightened emotions, partially attributed to the maturing brain.

  • Dramatic changes include:

    • Increased interconnectedness and specialization of brain areas (Giedd, 2015).

    • Ongoing myelination and development of neuron connections enhances thinking and processing efficiency.

    • For instance, language areas are myelinated during the first 13 years, facilitating language skills but making second language acquisition more challenging.

    • Synaptic pruning emphasizes the efficiency of the cortex while causing a reduction in its gray matter thickness.

    • Thicker corpus callosum strengthens inter-hemispheric communication.

    • Enhanced connections of the hippocampus with the frontal lobes improve memory integration into decision-making.

  • Limbic System and Prefrontal Cortex Mismatch:

    • The limbic system regulates emotion and reward and is sensitive to neurotransmitter dopamine, resulting in heightened social reward sensitivity.

    • The prefrontal cortex, responsible for impulse control and planning, matures substantially later than the limbic system.

    • This mismatch partly accounts for adolescents’ riskier behaviors and poor decision-making.

  • Mental Health Implications:

    • Around 50% of mental illnesses manifest by age 14, and 75% by age 24 (Giedd, 2015).

    • The adolescent brain is particularly susceptible to substance exposure, e.g., marijuana impacts the endocannabinoid system adversely (Weir, 2015).

  • Despite risks, the adolescent brain is adaptive, allowing social exploration and independence from family, which is beneficial for societal integration.

Physical Changes in Adolescence

  • Physical changes coincide with puberty, leading to puberty-related growth spurts and sexual maturity.

    • Primary and Secondary Sexual Characteristics:

    • Growth spurts and sexual characteristics develop, typically between ages 9–14 for girls and 10–17 for boys (Marshall & Tanner, 1986).

    • The pituitary gland stimulates the production of sex hormones:

    • Testosterone in boys,

    • Estrogen and progesterone in girls.

    • Effects of puberty:

    • Girls grow 2–8 inches (5-20 cm) while boys grow 4–12 inches (10-30 cm).

  • Common Indicators of Puberty:

    • Girls typically exhibit breast enlargement first between ages 10 and 12.

    • Boys develop broader shoulders and deeper voices, generally starting to grow facial hair between ages 14 and 16.

    • Both sexes may experience acne due to hormonal changes; about 85% of adolescents develop acne (Dolgin, 2011).

  • Menarche:

    • Represents the female’s first menstrual period, typically occurring around ages 12 or 13 (Anderson, Dannal, & Must, 2003).

    • Factors determining menarche include:

    • Genetics,

    • Diet,

    • Lifestyle.

    • Body fat plays a critical role in the onset of menarche, with very slim or malnourished girls at risk of delayed onset.

Male Anatomy

  • Males possess both internal and external reproductive organs crucial for reproduction.

    • Male sex organs include:

    • Penis,

    • Testes, which produce sperm and semen.

  • Sperm is produced continuously throughout the male's life, in contrast to the female's cyclical ovulation from the ovaries.

Female Anatomy

  • The external female genitalia, termed vulva, consists of:

    • Mons veneris,

    • Labia majora,

    • Labia minora,

    • Clitoris,

    • Vaginal opening,

    • Urethral opening.

  • Internal female reproductive organs include:

    • Vagina,

    • Uterus,

    • Fallopian tubes,

    • Ovaries.

    • Women are born with all their eggs, which are released in cycles during the menstrual cycle, typically every 28 days.

Effects of Puberty on Development

  • The average age for girls to begin menstruating has decreased from 16 to around 13 over the past century.

  • Social and psychological implications arise from early or late development:

    • Early maturing boys often gain physical advantages, potentially affecting popularity, conduct, and self-esteem, with risks for substance abuse and early sexual activity (Flannery, Rowe, & Gulley, 1993; Kaltiala-Heino et al., 2001).

    • Girls maturing early may face increased teasing, harassment, anxiety, depression, and risks for eating disorders (Ge et al., 2001; Graber et al., 1997).

The Brain and Sex

  • The brain regulates sexual impulses and behaviors:

    • The Cerebral Cortex is involved in sexual thoughts and fantasies.

    • The Limbic System governs emotions related to sex.

    • The Hypothalamus plays a pivotal role in sexual functions and controls the pituitary gland, which releases hormones linked to sexual behavior.

Hormones

  • Hormones influencing sexual desire include:

    • Oxytocin: Released during sexual activity and childbirth, known as the "hormone of love."

    • Prolactin: Involved in milk production in females post-birth.

    • Follicle-stimulating hormone (FSH): Triggers egg maturity in females and sperm production in males.

    • Luteinizing hormone (LH): Triggers the release of a mature egg during ovulation in females.

    • Testosterone: Major factor in male sexual motivation, linked to natural arousal responses.

    • Vasopressin: Influences male sexual arousal correlating with nicotine levels.

    • While male sexuality has been extensively studied, the relationship of female sexual motivation to hormones remains less understood but may include estrogen, progesterone, testosterone, oxytocin, and vasopressin.

Adolescent Pregnancy, Birth Control Methods, and Sexually Transmitted Infections (STIs)

  • By the end of high school, over 50% of adolescents report having engaged in sexual activity, highlighting the significance of sex education.

Teen Pregnancy

  • Adolescent pregnancy rates show a gradual decline since 1991, yet still higher than most industrialized countries.

    • Statistics: 2014 data shows a birth rate of 24.2 per 1,000 women aged 15–19, indicating a 9% drop from 2013.

Risk Factors for Adolescent Pregnancy

  • Links between adolescent pregnancy and various factors:

    • Higher risk in those with lower SES, disorganized neighborhoods, and previous instances of sexual abuse.

  • Conversely, strong parent-child relationships and supervision decrease risks.

Consequences of Adolescent Pregnancy

  • Only 40% of teen mothers graduate high school, with substantial negative outcomes including:

    • High rates of poverty post-birth.

    • Children born to adolescent mothers more likely to face academic challenges.

Sexually Transmitted Infections (STIs)

  • STIs, or sexually transmitted diseases, include:

    • Chlamydia,

    • Herpes,

    • HPV,

    • Gonorrhea,

    • Syphilis,

    • Trichomoniasis,

    • HIV/AIDS.

  • Use of condoms and practicing safe sex are critical to prevent STIs and unintended pregnancies.

Contraceptive Methods and Protection from STIs

  • Various contraceptive methods detailed:

    • IUD, hormonal implants, injections, pills, patches, and barriers (condoms).

  • Dual protection strategies should be emphasized to reduce both pregnancy and STD risk.

Adolescent Health: Sleep, Diet, and Exercise

Sleep Health

  • Adolescents require about 8-10 hours of sleep daily for optimal functioning, yet only a small percentage achieve this.

  • Risks of sleep deprivation include:

    • Poor academic performance,

    • Increased irritability,

    • Physical health issues.

  • Sleep cycles affect alertness, behavior, and necessitate changes in school start times to align with adolescent rhythms.

Nutrition and Eating Habits

  • Dietary Guidelines for Adolescents:

    • Nutritional choices become increasingly independent during adolescence.

    • Emotional changes heighten the need for proper nutritional guidance.

  • Food insecurity exists for some adolescents affecting development.

    • Hunger can lead to profound behavioral effects impacting overall well-being (Keys et al., 1950; Maslow's Hierarchy of Needs).

Weight Management

  • Girls: 1,400-2,200 calories; Boys: 1,600-2,600 calories based on activity levels during ages 9-13.

  • Importance of combining diet with physical activity for healthy weight maintenance.

  • Risks from childhood obesity include potential long-term chronic health issues.

Eating Disorders

  • Eating disorders can manifest during early adolescence:

    • Anorexia Nervosa: Fear of weight gain and energy intake restriction.

    • Bulimia Nervosa: Binge eating followed by compensatory behaviors.

    • Binge-Eating Disorder: Overeating without compensatory actions, leading to distress.

  • Consequences include severe physical and psychological issues; treatment involves therapy and nutritional support.

Drug and Substance Abuse

  • Impact on adolescents' physical and cognitive development through experimentation leading to addiction risks.

  • Main Types of Drugs include stimulants, depressants, opioids, and hallucinogens.

  • Consequences of drug use involve potential psychological and physical dependence, impacting social and emotional health.

    • Nicotine and alcohol present particular risks to developing adolescent brains.

    • Marijuana effects are especially pronounced on cognition, learning, and memory.

Mental Health Issues for Teens

Self-Harm and Suicidal Behavior

  • Signs of self-harm include unexplained injuries or changes in behavior, such as isolative tendencies.

  • Suicide remains a leading cause of death among adolescents with indicators including:

    • Talking about wanting to die,

    • Increased substance use,

    • Withdrawal from social environments.

  • Get Help information for need in crises, including national hotlines available.

Conclusion

  • Chapter highlights included:

    • Physical growth and changes during adolescence.

    • Weight management, obesity, and eating disorders.

    • Risks linked to adolescent pregnancy and sexual health.

    • Substance and drug abuse.

    • Various mental health issues facing teens.