Lifespan Development and Growth (Chapter 4)

What is Celiac Disease?

An immune-mediated condition in which eating gluten damages the small intestine.

The Endocrine System

your body's hormone messaging system.

How the system works

Hypothalamus → Directly controls the pituitary gland

Pituitary gland → Signals other glands and produces growth hormone

Hormones and growth → Help regulate growth and development

What are Endocrine Glands?

Little organs that release chemical messages called hormones into your bloodstream.

What are Hormones?

Chemical messengers that tell different parts of your body what to do.

What is the Pituitary Gland?

The “master gland” that helps control other endocrine glands and produces growth hormone.

What is Hypothalamus?

The brain structure that directly controls the pituitary gland.

What is the Growth Hormone?

Hormone produced by the pituitary gland that stimulates childhood physical growth and the adolescent growth spurt.

-Too much can cause unusually great growth; too little can limit adult height if untreated. Treatment works best when started early.

The Thyroid Gland

helps control two important things:

• Physical growth — how the body grows.

• Nervous system development — how the brain and nervous system develop.

Effects of Thyroid Deficiency & When

The important detail is that WHEN a person has a thyroid deficiency matters. The effects differ depending on the stage of development.

During pregnancy

If the mother has a thyroid deficiency, the developing child may experience intellectual problems.

During infancy or childhood

An untreated thyroid deficiency can lead to intellectual disability and slow growth.

Later in life

Physical growth can slow drastically, but the paragraph says brain damage is not expected because most brain growth has already occurred.

What are Androgens?

Male hormones that help trigger the adolescent growth spurt and the development of the male sex organs, secondary sex characteristics, and sexual motivation.

male sex hormones and adolescent growth spurt

Testosterone and other androgens stimulate growth hormone production, contributing to the growth spurt.

What does testosterone do before birth and during adolescence?

What are the main functions of estrogen and progesterone?

Estrogen supports female sexual development and menstrual cycles; progesterone supports conception and pregnancy.

What do adrenal androgens contribute to in both sexes?

Bone and muscle maturation and sexual motivation.

What roles do thyroid and adrenal hormones play in adulthood?

Thyroid hormones help metabolize food; adrenal hormones help the body cope with stress. Sex-hormone levels can decline with age.

What are the CNS and PNS?

The central nervous system (CNS) consists of the brain and spinal cord. The peripheral nervous system (PNS) consists of neural tissue extending throughout the body.

What are Neurons and its parts?

• a nerve cell that sends and receives information.

Parts of a neuron

• Dendrites: receive signals.

• Axon: carries electrical signals away from the neuron.

• Synapse: tiny gap where one neuron communicates with another.

• Neurotransmitters: chemicals released to communicate across that gap.

neurotransmitters can either stimulate another neuron's activity (encourage it to act) or inhibit it (reduce or prevent its activity).

What are the functions of dendrites, axons, synapses, and neurotransmitters?

Dendrites receive signals;

axons transmit signals;

synapses are tiny gaps between neurons;

Neurotransmitters are chemicals that can stimulate or inhibit another neuron's activity.

What is Myelin?

the fatty, insulating covering around many axons.

Analogy: Imagine a neuron's axon is an electrical wire. THIS is the insulation around the wire. It helps neural messages travel faster.

What is Myelination?

• the process of axons becoming covered with myelin.

• It begins before birth and continues for many years after birth, even into adulthood.

The big idea: as different brain areas become myelinated, certain abilities improve.

High Yield Examples of Myelination

Brain area / process	Developmental connection
Visual cortex	Myelination is largely complete by age 1, alongside advances in vision.
Language-related brain areas	Rapid myelination is associated with toddlers' vocabulary spurt.
Prefrontal lobes	Myelination during adolescence supports reasoning about abstract ideas, such as truth and justice.
Attention pathways	Continued myelination helps explain improving attention and concentration with age.
Into adulthood	Continued myelination may help adults integrate thoughts and emotions more effectively than teenagers.

Sequence of Myelination

myelination progresses from the spinal cord → hindbrain → midbrain → forebrain.

How does myelination relate to development?

It supports developing vision, vocabulary, abstract reasoning, attention, and emotional regulation.

What are the 3 principles of growth?

1. Cephalocaudal = head to tail

Growth proceeds from the head downward toward the feet.

Example: Babies develop control of their head before they develop control of their legs.

2. Proximodistal = center outward

Growth proceeds from the center of the body toward the extremities.

Example: The chest and internal organs develop before the arms, hands, and fingers.

3. Orthogenetic = simple to complex

Development moves from general, undifferentiated forms toward specialized parts that become organized into functioning systems.

Example: One cell develops into specialized cells, which organize into systems such as the brain and digestive system.

Newborn’s head v. Adult’s head

The newborn's head accounts for about 25% of body length and 13% of body weight, compared with about 12% of adult height and 2% of adult weight. These numbers illustrate cephalocaudal growth.

Health is shaped by what 4 interacting areas?

Biological — your body

Genes, prenatal experiences, immune function, stress responses, and how your body processes nutrients.

Psychological — your mind

Personality, emotions, beliefs, optimism or pessimism, and coping skills. These can influence health behaviors and how someone responds to treatment.

Social — your relationships and circumstances

Family care, nutrition, social support, access to healthcare, and financial resources.

Cultural — your broader cultural context

Cultural beliefs and practices that can influence how people understand health, make healthcare decisions, and seek treatment.

The important part: These four areas interact. Health isn't determined by any one factor alone.

For example, someone might have a biological predisposition to a health problem, experience stress, lack family support, and face financial barriers to healthcare. All of these can affect their overall health.

How the 4 factors effect health (textbook)

• Prenatal experiences: A mother's smoking or alcohol use during pregnancy may influence a child's later health predispositions.

• Psychological factors: Beliefs and fears can lead someone to delay a diagnostic test or stop taking medication because of side effects.

• Social factors: Family care, nutrition, immunization, education, social support, poverty, and access to healthcare can affect health.

• Happiness and optimism: The textbook describes research associating happiness and optimism with longer life. Remember this as an association, not proof that happiness alone causes someone to live longer.

What is Synaptogenesis?

building more connections between neurons.

• Growth of synapses/connections between neurons.

What is Synaptic Pruning?

removing connections that are unnecessary or rarely used.

• Elimination of unnecessary or unused connections.

Synaptogenesis & Synaptic Pruning Facts

synaptogenesis is especially prominent from birth to about age 7, while synaptic pruning is highlighted from about ages 7–15. These are approximate developmental patterns, not rigid cutoffs.

What is Neuroplasticity?

• the brain's ability to change in response to experience.

The brain uses experiences to help strengthen and organize its connections. Both genes and the environment matter.

For example, babies need opportunities to explore, see, hear, move, and interact with their surroundings. A stimulating environment can support brain development, while deprivation, disease, or exposure to harmful substances can interfere with it.

• It is especially strong early in life, allowing experiences to shape brain development and sometimes allowing the brain to compensate for injury.

Must Know Facts

Synaptogenesis

Growth of synapses/connections between neurons.

Synaptic pruning

Elimination of unnecessary or unused connections.

Neuroplasticity

The brain's ability to change in response to experience.

Genes and experience

Brain development is influenced by both genetic programming and environmental experiences.

Early brain development

Brain plasticity is greatest early in development, making the brain especially responsive to experience.

Sensitive period

An early period when experience has a particularly strong influence on brain development; described here as beginning in late prenatal development and lasting into childhood.

Environment

Enriched experiences can support brain development; deprivation and harmful exposures can interfere with it.

How do genes and the environment influence brain development?

Genes provide a developmental foundation, while experiences and environmental conditions help shape neural connections. Enriched experiences can support development, while deprivation or harmful exposures can interfere with it.

The Baby’s Growth

• Infants grow quickly. By age 2, children have reached about half their eventual adult height.

• Growth happens in spurts, not at a steady rate. Babies may go weeks without measurable growth, then grow noticeably in a short time. Growth spurts may be associated with longer sleep and irritability.

• Bones are still developing. A newborn's bones are soft and flexible. They gradually harden through a process called ossification.

• Fontanelles are the soft spaces between an infant's skull bones. They allow flexibility during birth, and the bones gradually harden as the child develops.

• Muscles get stronger as they grow. Infants already have the muscle cells they will have, but their muscles grow and become stronger over time.

What is ossification?

the natural biological process of bone formation and tissue hardening. It is also known as osteogenesis

What are Fontanelles?

the soft spaces between an infant's skull bones. They allow flexibility during birth, and the bones gradually harden as the child develops.

Must Know Details about Baby’s development

Newborn size

About 20 inches long and 7–7½ pounds

Age 2

About half of eventual adult height; average weight 27–30 pounds

Growth spurts

Growth happens in bursts, with periods of little or no measurable growth in between

Ossification

The process of hardening into bone

Fontanelles

Soft spaces between an infant's skull bones

Anterior fontanelle

The largest gap on top of the head; typically fills in between 9 and 18 months

Muscle development

Strength increases as muscles grow

What are Reflexes?

an unlearned and involuntary response to a stimulus, such as when the eye automatically blinks in response to a puff of air.

What are 2 types of Reflexes

1. Survival reflexes: Help the baby stay alive, such as breathing, sucking, and swallowing.

2. Primitive reflexes: Automatic movements that usually disappear during early infancy as the brain develops. Doctors can use their presence and disappearance to assess neurological development.

Types of Newborn Reflexes

Survival reflexes

Breathing, eyeblink, pupil response, rooting, sucking, and swallowing.

Rooting reflex

Baby turns toward a touch on the cheek, helping locate the breast or bottle.

Sucking reflex

Helps the baby obtain nourishment.

Babinski reflex

Stroking the sole causes the toes to fan and then curl.

Grasping reflex

Baby curls fingers around something touching the palm.

Moro reflex

Sudden noise or change in head position causes the baby to extend the arms, arch the back, then bring the arms inward.

Stepping reflex

Baby makes stepping movements when held upright with feet touching a surface.

Primitive reflexes

Usually disappear as higher brain centers develop; their presence and disappearance can help assess neurological health.

Newborn Reflexes and how long they last

• Grasping reflex: disappears in the first 3–4 months, replaced by voluntary grasping.

• Moro reflex: disappears by about 4 months, while the ordinary startle response remains.

• Stepping reflex: disappears in the first 8 weeks, unless the infant has regular opportunities to practice it.

• Babinski reflex: disappears by 12–18 months.

6 Infant Behavioral States and Sleep

• Deep sleep: Very still; relatively unaware of surrounding stimulation.

• Active sleep: Rapid eye movements; wakes more easily.

• Quiet alert: Little movement, focused eyes, engaged with the caregiver or environment.

• Active alert: More body movement and less focused eyes; too much stimulation may lead to fussiness.

• Drowsy: Relaxed and close to falling asleep.

• Crying: May signal hunger, discomfort, or overstimulation.

Sleep Facts about Baby

• Newborns spend about 50% of their sleeping time in REM (active) sleep.

• Infants older than 6 months spend about 25–30% of sleep in REM.

• By around 3 months, most infants begin developing a more predictable sleep–wake cycle.

• By around 6 months, sleep–wake patterns are fairly stable for most infants.

• REM sleep may support learning and memory, although the textbook presents this as a possible explanation.

Health and Wellness of Baby (Infant)

Nutrition matters because an infant's brain and body are growing rapidly. The textbook discusses research finding that breastfed infants had a slight advantage in myelination and early cognitive skills compared with formula-fed infants. Among formula-fed infants in that study, outcomes were strongest for the formula most similar in nutritional composition to breast milk.

The textbook also explains that infant health is affected by medical conditions present at birth, premature birth, and preventive healthcare.

What are Congenital Malformations?

Conditions or defects present at birth, which may result from genetic factors or prenatal events.

What is Low Birth Weight?

A major risk to infant health, often associated with premature birth. Health complications may continue beyond infancy.

What is the purpose of Vaccinations for infants?

Help protect infants against diseases such as polio, measles, and pertussis.

What is preventative care?

Prenatal care, well-baby visits, and following illness-prevention recommendations can improve infant health.

Must Know Facts (Infant health and wellness)

Nutrition	Important for rapid brain development and myelination.
Congenital malformations	Defects present at birth; listed as the leading cause of infant mortality in this section.
Low birth weight	Second-leading cause of infant mortality in the listed statistics; often associated with premature birth.
Prematurity	Complications of premature birth account for 35% of infant deaths, according to the textbook.
Vaccinations	Protect against diseases that can seriously compromise infant health.
Preventive healthcare	Includes prenatal care, well-baby visits, and recommended vaccinations.

Potential quiz detail: The textbook lists the six causes of infant mortality in this order:

1. Congenital malformations

2. Low birth weight

3. Maternal complications

4. Sudden infant death syndrome (SIDS)

5. Unintentional injuries

6. Cord and placental complications

Physical Growth (The Child)

• From age 2 until puberty, children gain about 2–3 inches and 5–6 pounds per year.

• Growth charts compare a child's height and weight with typical patterns for children of the same age and gender.

• Bones continue to harden, muscles strengthen, and body proportions become more adult-like.

What is Lateralization?

means the two sides of the brain become specialized for different functions.

Left hemisphere

Usually associated with language, analytical reasoning, and processing information step by step (sequential processing). It controls the right side of the body.

Right hemisphere

Usually associated with spatial information, visual-motor processing, and emotional aspects of information (simultaneous processing). It controls the left side of the body.

Important: The brain's hemispheres work together. It is an oversimplification to say that the left side is only logical and the right side is only emotional.

What is the Corpus Callosum?

a thick, C-shaped bundle of more than 200 million nerve fibers (axons) located deep within the center of the brain. It acts as the primary bridge connecting the left and right cerebral hemispheres.

Must Know Facts (Lateralization)

Term	Meaning
Lateralization	Specialization of functions between the brain's two hemispheres.
Left hemisphere	Usually dominant for language; sequential processing and analytical reasoning.
Right hemisphere	Spatial and visual-motor processing; emotional content.
Corpus callosum	Bundle of neural connections linking the two hemispheres.
Early lateralization	Signs appear before birth and in newborn behavior.
Neuroplasticity	The other hemisphere may sometimes compensate for functions lost through damage.

One interesting textbook detail: although language is processed mainly in the left hemisphere for most people, the right hemisphere can sometimes support language function when the left hemisphere is removed or damaged. This illustrates the brain's capacity to adapt.

Leading Cause of Accidental Deaths (Age Range)

Age group	Top 3 causes of accidental death (ranked)	Top 3 causes of injury (not death, ranked)
Ages 1–4	1. Drowning 2. Motor-vehicle accident 3. Fire/burns	1. Falling 2. Struck by/against something 3. Other, bite/sting
Ages 5–9	1. Motor-vehicle accident 2. Drowning 3. Fire/burns	1. Falling 2. Struck by/against something 3. Other, bite/sting
Ages 10–14	1. Suicide, suffocation 2. Motor-vehicle accident 3. Suicide, firearm	1. Falling 2. Struck by/against something 3. Unintentional overexertion

Bonus: Ages 15–24 (also included in the chart)

Rank	Causes of death	Causes of nonfatal injury
1	Motor-vehicle accident	Struck by/against something
2	Unintentional poisoning	Falling
3	Homicide, firearm	Motor-vehicle accident

3 big topics in Children Health and Wellness

• Accidents: Injuries are a leading cause of death during childhood. Drowning is the leading accidental cause of death for ages 1–4, while motor vehicle accidents are the leading accidental cause for ages 5–9 in the textbook's table.

• Nutrition: Children's diets are influenced by parents, schools, and neighborhood food options. Poverty and limited access to healthy food can make healthy eating harder.

• Physical activity: Children should get at least 60 minutes of moderate or vigorous physical activity daily, according to the textbook. Exercise supports physical fitness, but also cognitive functioning, academic performance, and classroom behavior.

The big idea is that children's health isn't just about individual choices. Their home, school, neighborhood, family resources, and temperament all play a role.

Must Know Facts (Childrens Health and Wellness)

Leading cause of death in childhood

Accidents and injuries overall.

Ages 1–4

Drowning is the leading accidental cause of death.

Ages 5–9

Motor vehicle accidents are the leading accidental cause of death.

Nutrition

Parents' habits, neighborhood food availability, and school meal programs influence children's eating.

BMI

Body mass index; a measure calculated using height and weight and used as a marker of body fat.

Physical activity

At least 60 minutes of moderate or vigorous activity each day.

Screen time

High screen time is associated with less physical activity and, in some studies, poorer cognitive performance and greater risk of overweight.

Exercise benefits

Supports physical fitness, cognitive and psychological functioning, and academic performance.

What are Nonfatal Injuries?

Falls and being struck by something and doesn’t result in death

Important Details (Children’s health and wellness)

• Environment matters: Safe outdoor spaces and access to portable play equipment can encourage children to be more active.

• School meals: School breakfast and meal programs can support healthier eating, although school meals are not automatically perfect nutritionally.

• Individual differences: A child's temperament can affect how active they are, even when the environment encourages exercise.

What is Puberty?

the processes of biological change that result in attaining sexual maturity and becoming capable of producing a baby.

What is Gray Matter?

Think: processing information.

• Increases during late childhood.

• Peaks, then decreases during adolescence — an inverted-U pattern.

• This pattern is associated with synapse growth followed by synaptic pruning.

• The textbook says it is fully developed by the 20s.

processing; grows, peaks, then decreases.

What is White Matter?

Think: communication between brain areas.

• Consists of bundles of myelinated axons.

• Increases steadily throughout adolescence.

• This is associated with ongoing myelination, which helps brain signals travel efficiently.

communication; steadily increases.

Why do teenagers sometimes take more risks?

The brain's systems don't mature at the same rate.

• Limbic reward system matures earlier

Helps drive emotions, reward-seeking, and motivation. Teens may be drawn to exciting or rewarding experiences.

• Prefrontal control areas mature later

Help with judgment, planning, and evaluating consequences.

The result: A teenager may be drawn toward a reward before fully considering the risks.

This helps explain why some teens take risks involving alcohol, drugs, sex, or driving. It does not mean all teenagers are reckless.

Other details from your textbook:

• Stronger working memory is associated with less risk-taking.

• A positive relationship with parents can help protect teens.

• Being around peers can increase risk-taking.

• Alcohol can make risky behaviors more likely, including unsafe sex, riding with an impaired driver, fighting, and academic or legal problems.

Researcher Laurence Steinberg Solution for teenage risk taking

Researcher Laurence Steinberg argues that simply telling teens to make better decisions often isn't enough.

Instead, adults can change the environment to reduce exposure to risky situations, for example:

• Limit access to alcohol, drugs, and cigarettes.

• Reduce excessive unstructured time.

• Consider later school start times so teens can get enough sleep.

The key concept is that adults can make environments safer while the adolescent brain continues developing.

What is a concussion?

A brief loss of normal brain function after a hit or blow to the head.

Possible symptoms include:

• Headache

• Sensitivity to light or sound

• Dizziness or feeling foggy

• Slower reaction time

What is CTE (chronic traumatic encephalopathy)

A degenerative brain disease associated with repeated head impacts.

Possible symptoms include:

• Memory loss

• Poor impulse control

• Depression and mood changes

• Eventually, dementia

Important distinctions between Concussions and CTE

• Many concussions are classified as mild, and symptoms often resolve within weeks.

• Repeated head impacts can have lasting effects, even when each impact isn't diagnosed as a concussion.

• CTE can currently be definitively diagnosed only by examining the brain after death, according to the textbook.

• The textbook reports that some studies found high rates of CTE in donated brains of former football players. These donated samples should not be treated as representative of all football players.

• The American Academy of Neurology recommends that athletes with symptoms of altered consciousness not return to play until examined and cleared by a qualified medical professional.

Adolescent Growth Spurt

• Growth hormone increases during adolescence, triggering the growth spurt.

• Girls reach peak growth rate around age 12.

• Boys reach peak growth rate around age 14.

• Muscles grow rapidly in both sexes, but boys typically gain a greater proportion of muscle mass.

• Girls tend to gain more body fat around the breasts, hips, and buttocks.

• Boys tend to develop broader shoulders.

What is Adrenarche?

Typically begins around ages 6–8

The adrenal glands increase production of adrenal androgens in both boys and girls. This contributes to the development of pubic and underarm hair.

What is Menarche?

Girls · typically around age 12.5

A girl's first menstruation. Menstruation is the shedding of the uterine lining.

What is Semenarche?

Boys · typically around age 13

A boy's first ejaculation.

Puberty Changes

• Girls: Breasts develop, pubic hair appears, and menstruation begins.

• Boys: Testes and scrotum enlarge, the voice deepens, and ejaculation begins.

• Gonadal hormones are hormones produced by the testes or ovaries. They play a major role in sexual maturation and secondary sex characteristics.

• Menarche does not necessarily mean ovulation has begun. Some girls can ovulate from the time menstruation starts, while others begin ovulating later. Similarly, boys may not produce viable sperm until after their first ejaculation.

What are Gonadal Hormones?

hormones produced by the testes or ovaries. They play a major role in sexual maturation and secondary sex characteristics.

Genes and Hormones (What Determines when puberty starts)

• Early or late maturation tends to run in families.

• Identical twins often begin and finish growth spurts at similar times.

• The textbook estimates that about 75% of variation in the timing of menarche is attributable to genetic effects.

• The hypothalamus stimulates the endocrine system, triggering the hormonal changes involved in puberty.

Environment (What determines when puberty starts?)

Factors associated with puberty timing include:

• Nutrition and medical care

• Childhood overweight or obesity

• Strenuous physical activity and severe undernutrition

• Stress and family circumstances

• Exposure to certain chemicals that may alter hormone production

What is the Secular Trend?

a historical trend toward earlier maturation and greater body size.

The textbook describes the average age of menarche declining from about 17 in the mid-19th century to about 14 in the mid-20th century, and to around 12.5 in the United States more recently.

Possible contributors include improved nutrition, medical care, higher obesity rates, and exposure to chemicals that affect hormones.

One important nuance: the textbook discusses research linking a father's absence from the home with earlier puberty in girls, but warns that stress and other circumstances may explain the association. It does not establish that a father's absence itself causes early puberty.

Psychological effects of puberty

Girls

• May become more self-conscious about appearance and body image.

• May experience body dissatisfaction and unhealthy dieting.

• Puberty can coincide with mood changes and increased risk of depression or eating disorders.

• Early-maturing girls may face teasing, bullying, or pressure from older peers.

Boys

• Often feel more positively about body changes, muscle gain, and a deeper voice.

• Boys who mature late or remain shorter than peers may experience anxiety, depression, or feelings of inadequacy.

• As late-maturing boys catch up physically, some of these difficulties may decrease.

Family relationships

• Adolescents seek more independence.

• Parent–teen conflict may increase.

• Most conflicts concern everyday matters, such as chores, curfews, or loud music, rather than major values.

• Parents who maintain open communication can help adolescents navigate these changes.

Important: These are general patterns, not rules that apply to every girl or boy.

Early versus late maturation

Group	Possible effects of early maturation	Possible effects of late maturation
Boys	Greater social acceptance, perceived attractiveness and confidence; but increased risk of substance use, aggression, bullying, or delinquency	More anxiety or depression; potentially less alcohol or drug use during adolescence
Girls	More body dissatisfaction, teasing, depression, and potential involvement with older peers and risky behaviors	Some anxiety while waiting to mature; may have academic advantages relative to early-maturing girls

Why can early maturation be difficult for girls?

Girls typically begin puberty about two years earlier than boys. An early-maturing girl may feel out of place among classmates who have not developed yet. She may also socialize with older peers, which can increase exposure to dating and other risky behaviors.

The textbook also describes research suggesting that some behavioral and adjustment problems may exist before early puberty becomes visible. Therefore, we shouldn't assume early puberty alone causes later emotional or behavioral difficulties.

How can early maturation affect boys and girls differently?

Early-maturing boys may gain social acceptance but have increased risk of problem behaviors. Early-maturing girls may experience more body dissatisfaction, teasing, depression, and exposure to older peers.

Adolescent Physical Fitness and Weight

Even though adolescence should be a time of good physical fitness, many teens are inactive.

• Only 25% of teenagers get the recommended 60 minutes of physical activity daily (according to the textbook’s cited source).

• Inactivity can contribute to high blood pressure, high cholesterol, and high blood sugar, increasing later risk of heart disease.

• Girls tend to become less active than boys during adolescence, although the gap has narrowed.

• Improving fitness isn't just about telling teens to exercise. Their environment matters too, including safe sidewalks, bike paths, and school start times.

Adolescent Weight and Obesity

• The textbook defines obesity here as being 20% or more above ideal weight for height, age, and sex.

• Sedentary lifestyles and consuming too many low-nutrient, high-calorie foods and drinks contribute to weight gain.

• Obesity-related metabolic syndrome (MeTS) includes risk factors such as high blood pressure, unhealthy cholesterol levels, and diabetes.

• In one study, adolescents with MeTS scored lower on some cognitive measures, especially math achievement, and had some attention and mental-flexibility difficulties. This shows an association, not proof that obesity directly caused the differences.

What contributes to Obesity?

The textbook emphasizes that obesity usually reflects both nature and nurture.

• Nature: Genetic factors inherited from parents may increase a teen’s tendency to gain weight.

• Nurture: Family habits, food choices, physical activity, stress, and the surrounding environment can influence weight.

• Teens may adopt their friends’ habits, including inactivity and unhealthy eating.

Environmental Contributors to Obesity

Factor	Simple explanation
Inactive lifestyles	People burn fewer calories when they sit more.
Portion sizes	Food and drink servings have grown larger.
Fat content	The textbook describes increases in fat consumption over time.
Sugar	High sugar consumption adds calories.
Stress	Stress is associated with belly fat and unhealthy snacking.
Poverty	Limited resources can make nutritious food and healthy environments harder to access.

Why do teenagers struggle to get enough sleep?

1. Biological changes

During puberty, melatonin production shifts later, and the circadian rhythm pushes teens to fall asleep later at night.

2. Early school start times

Teens may naturally fall asleep late but still have to wake up around 6:30 a.m. for school.

The textbook calls this combination the “perfect storm” for insufficient sleep.

What happens when teens don't get enough sleep?

• More daytime sleepiness and lower motivation.

• Difficulty concentrating and short-term memory problems.

• Greater irritability, depression, and difficulty managing frustration.

• More difficulty controlling emotional responses, potentially including anger or aggression.

• Increased caffeine use, which can further disrupt sleep.

Important research findings from your textbook:

• Students who got a good night's sleep before a test performed better than students who sacrificed sleep to study longer.

• In a Seattle study, moving high school start time from 7:50 a.m. to 8:45 a.m. resulted in at least 30 minutes more sleep per night, fewer absences, less daytime sleepiness, and improved science grades from a C+ average to a B− average.

Big takeaway: Sleep is not wasted study time. Adequate sleep supports learning, memory, attention, and emotional regulation.

What is Neurogenesis?

The creation of new neurons (brain cells).

• Exercise may promote neurogenesis.

• The hippocampus is involved in learning and memory.

• Scientists disagree about how much neurogenesis continues in adult humans. Some studies found evidence in older adults; others did not.

What is Neuroplasticity?

The brain's ability to change, reorganize, and form new connections in response to experience.

• Continues throughout life.

• Can be supported by physical exercise, mental activity, and enriched experiences.

• Can help the brain adapt after injury.

What is Synaptogenesis?

forming new connections between neurons.

What is Angiogenesis?

the development of new blood vessels.

What happens to the brain as we age?

Normal aging does not automatically mean dementia or Alzheimer's disease.

The textbook describes several typical changes:

• Brain weight and volume decrease, slowly around ages 30–50 and more quickly after age 70.

• Gray matter decreases, particularly in the frontal cortex. This may affect attention, executive functioning, and retrieving words.

• White matter changes may contribute to slower information processing and reduced episodic memory.

• Neurotransmitter levels and blood flow to the brain may decline.

• Older adults may need more time to complete tasks.

But there is a positive side: dendrites can continue growing in response to experience, supporting learning and memory. Exercise and mentally stimulating activities may help maintain brain health.

The BIG THREE: Maintenance, reserve, and compensation

Maintenance = keeping the brain in good condition

Regularly protecting and caring for neurons and neural connections, and helping repair damage when possible.

Think: Maintaining a car so it keeps working.

Reserve = resources built up over a lifetime

These resources can help offset age-related cognitive decline.

• Brain reserve: The physical resources of the brain, such as neurons and neural connections — think hardware.

• Cognitive reserve: Mental resources developed through education, learning, work, and other challenging activities — think software.

Compensation = recruiting other brain areas to help

When a task becomes difficult, the brain may use additional areas to help complete it.

Think: Your usual route is blocked, so you find another route.

How to tell the Big THREES apart on a quiz

If the question describes…	Answer
Protecting brain health and neural connections	Maintenance
Building mental resources through education and learning	Cognitive reserve
Having more physical brain resources, such as neurons	Brain reserve
Using additional brain regions to complete a task	Compensation

One more textbook detail: the chapter describes research in which older adults who maintained their cognitive performance showed more activity in parts of the prefrontal cortex and hippocampus during a memory task.

How does culture shape the adult brain?

The textbook explains that cultural experiences can be associated with different patterns of brain activity. For example, research comparing East Asian and Western participants found differences in brain activity when viewing objects and backgrounds.

Main takeaway: The brain remains responsive to experiences and the cultural environment throughout life.

What is neurocognitive maintenance?

Protecting, maintaining, and when possible repairing the brain and its neural connections.

Changes in the reproductive system (In men)

• Testosterone levels in younger men are usually highest in the morning and lower in the evening.

• After about age 40, daily fluctuations become less pronounced.

• After age 60, testicular volume begins to decline, contributing to lower testosterone levels.

• Benign prostatic hyperplasia (BPH): noncancerous enlargement of the prostate gland. It can cause frequent urination and difficulty fully emptying the bladder.

What is Benign prostatic hyperplasia (BPH)?

noncancerous enlargement of the prostate gland. It can cause frequent urination and difficulty fully emptying the bladder.

Changes in the reproductive system (In women: PMS vs. PDD)

PMS — Premenstrual syndrome

• Symptoms before menstruation, such as bloating, moodiness, breast tenderness, and headaches.

PDD — Premenstrual dysphoric disorder

• A more severe condition involving significant emotional symptoms as well as physical symptoms. It can disrupt work and relationships.

Your textbook says up to 10% of women experience PMS symptoms severe enough to interfere with daily activities, and approximately 2–3% may experience the severe form it calls PDD.

Quiz distinction: PMS involves premenstrual symptoms; PDD involves particularly significant emotional symptoms alongside physical symptoms and can be disabling.

What is Menopause? (Female)

the end of menstrual cycles and reproductive capacity as estrogen and other reproductive hormones decline.

• Usually occurs between ages 45 and 54, according to the textbook.

• The transition typically takes 5–10 years.

• Periods become irregular before eventually stopping.

• Symptoms can include hot flashes, vaginal dryness, and discomfort during intercourse. Some women experience few or no symptoms.

• Hormone replacement therapy (HRT) uses estrogen and progestin to help relieve symptoms. The textbook notes that treatment decisions involve weighing benefits and risks.

• Exercise and adequate sleep may help women with milder symptoms.

Important concept: It is not the same experience for every woman.

Cultural attitudes and personal experiences influence how women experience THIS. The textbook challenges the stereotype that menopausal women are automatically irritable, depressed, or emotionally unstable.

What is Andropause? (Male)

also called age-associated hypogonadism in your textbook, refers to a gradual decrease in testosterone associated with aging.

Possible symptoms include:

• Lower sexual desire (libido)

• Fatigue and reduced energy

• Erection difficulties

• Memory problems

• Loss of pubic hair

The textbook states that by age 80, men may have 20–50% of the testosterone levels they had at age 20.

What is Erectile Dysfunction?

difficulty achieving or maintaining an erection for intercourse. It can occur even when testosterone levels are sufficient. The textbook identifies sildenafil (Viagra) as a treatment.