5—Physical Development in Infancy

McGraw-Hill © 2007 The McGraw-Hill Companies, Inc. All rights reserved..

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5—Physical Development in Infancy

• Body Growth and Change • The Brain • Sleep• Health • Summary


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Body Growth and Change

• Growth Patterns– Cephalocaudal pattern:

• The sequence in which the greatest growth occurs at the top—the head—with physical growth in size, weight, and feature differentiation gradually working from top to bottom.

– Proximodistal pattern: • The sequence in which growth starts at the center of

the body and moves toward the extremities.


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Changes in Proportions of the Human Body During Growth

• Refer to Figure 5.1


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• Infancy and Childhood– Infancy

• The average North American newborn is 20 inches long and weighs 7½ pounds.

• Most newborns lose 5% to 7% of their body weight in the first several days of life.

• Newborns double their birth weight by the age of 4 months and nearly triple it by their first birthday, but growth slows in the second year; by age 2, children average 32 to 35 inches in height—nearly half their adult height.


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• Infancy and Childhood– Early Childhood

• The percentage of increase in height and weight decreases each year for preschoolers, and girls are only slightly smaller and lighter than boys.

• Body fat declines slowly during preschool years; girls have more fatty tissue than boys and boys have more muscle tissue than girls

• Growth patterns vary due to heredity and environmental experiences.


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• Infancy and Childhood– Early Childhood

• Physical problems, growth hormone deficiency, or emotional difficulties may retard growth.

• Growth hormone deficiency: The absence or deficiency of growth hormone produced by the pituitary gland.

– Can be treated with injections of growth hormone for several years.


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• Infancy and Childhood– Middle and Late Childhood (Ages 6 to 11)

• Slow, consistent growth averaging 2 to 3 inches a year.

• Muscle mass increases; body fat decreases.• Improved muscle tone and strength.• Bones continue to harden.


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• Puberty– A period of rapid physical maturation involving

hormonal and bodily changes that take places in early adolescence.

– Determinants of Puberty• There are wide variations in onset and progression.• Age of onset has been steadily dropping around the

world, with average age of menarche dropping 2 to 4 months per decade during the twentieth century.


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– Determinants of Puberty (continued)• Menarche: A girl’s first menstruation, with normal

age ranging from 9 to 15 years old.• Timing for the emergence of puberty is hereditary,

but is influenced by environmental factors such as health, weight, and stress.


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– Determinants of Puberty (continued)• Hormones: Powerful chemical substances secreted

by the endocrine glands and carried through the body by the bloodstream.

• In puberty, secretion of key hormones is controlled by the interaction of the hypothalamus, the pituitary gland, and the gonads (sex glands).


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– Determinants of Puberty (continued)• Adrenarche involves hormonal changes in the

adrenal glands (about ages 6 to 9).• Gonadarche involves sexual maturation and the

development of reproductive maturity .• Culmination of gonadarche in girls is menarche

(first menstruation), in boys is spermarche (the first ejaculation of semen).


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– Determinants of Puberty (continued)• Key hormonal changes of gonadarche are

androgens (main class of male hormones, e.g., testosterone) and estrogens (main class of female hormones, e.g., estradiol).

• These hormones are present in both males and females, but in different concentrations.

• Growth during puberty is facilitated by hormones such as cortisol, testosterone, and estrogen.


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Hormone Levels by Sex and Pubertal Stage for Testosterone and Estradiol



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• Puberty (continued)– Weight and Body Fat

• Undernutrition can delay puberty: for menarche to begin and continue, fat must make up 17% of a girl’s body weight.

• Amenorrhea, an absence or suppression of menstruation, occurs in anorexic adolescents and females participating in some sports.

• Leptin, a hormone released by fat cells, signals the adequacy of fat stores for reproduction and maintenance of pregnancy at puberty.


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• Puberty (continued)– Growth Spurt

• Occurs approximately 2 years earlier for girls than for boys.

• Mean beginning of the growth spurt in the U.S. is age 9 for girls and age 11 for boys.

• Height and weight follow approximately the same timetable, and 50% of adult body weight is gained during adolescence.

• Girls increase in hip width, boys increase in shoulder width.


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Pubertal Growth Spurt



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• Puberty (continued)– Sexual Maturation

• The three most noticeable areas of sexual maturation in boys include penis elongation, testes development, and growth of facial hair.

• The two most noticeable areas of sexual maturation in girls include breast enlargement and the appearance of pubic hair.

• Menarche occurs late in the pubertal cycle.


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• Puberty (continued)– Body Image:

• Adolescents are preoccupied with their bodies.• Girls are generally less happy than boys with their

bodies.


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• Puberty (continued)– Early and Late Maturation

• Early-maturing adolescents have more positive body image than late-maturing adolescents, but by their 30s, late-maturing boys have a more positive identity than early-maturing boys.

• Early-maturing girls have an increased vulnerability to socioemotional problems.


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Normal Range and Average Development of Sexual Characteristics in Males and Females



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Review and Reflect: Learning Goal 1

• Discuss developmental changes in the body– Review

• What are cephalocaudal and proximodistal patterns?• What changes in height and weight take place in

infancy and childhood?• What changes characterize puberty?


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– Reflect• Did you experience puberty early, late, or on-time?

How do you think this affected your social relationships and development?


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The Brain

• Brain Physiology– The brain has two hemispheres.– The forebrain, or top portion, is covered by a layer of

cells called the cerebral cortex, which is responsible for 80% of the brain's volume; it is critical in perception, thinking, language, and other functions.


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The Brain

• Brain Physiology (continued)– Four lobes of the cortex:

• Frontal lobes: Govern voluntary movement, thinking, personality, and intentionality or purpose.

• Occipital lobes: Control vision.• Temporal lobes: Govern hearing, language

processing, and memory.• Parietal lobes: Govern spatial location, attention,

and motor control.


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The Brain

The Human Brain’s Hemispheres



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The Brain

The Brain’s Four Lobes



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The Brain

• Brain Physiology (continued)– Limbic System

• Hypothalamus (monitors eating, drinking, and sex)• Pituitary gland (controls growth, regulates other

glands)• Amygdala (governs emotions) • Hippocampus (governs memory and emotion)


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The Brain

• Brain Physiology (continued)– Neuron

• Nerve cell that handles information processing at the cellular level.

• Axons send electrical signals away from the central part of the neuron, across synaptic gaps, via chemical substances called neurotransmitters.

• Dendrites of different neurons receive the signals.• Myelin sheath: Layer of fat cells that helps

impulses travel faster along the axon.


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The Brain

The Neuron



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The Brain

• Brain Physiology (continued)– Neural circuits are clusters of neurons that work

together to handle particular types of information.• The neural circuit for attention and working

memory uses the neurotransmitter dopamine and lies in the prefrontal cortex.


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The Brain

The Prefrontal Cortex



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The Brain

• Brain Physiology (continued)– Lateralization

• Specialization of function in one hemisphere of the cerebral cortex or the other.

• Complex thinking requires both hemispheres.


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The Brain: Infancy

– Brain development occurs extensively in utero.– Because of the extensive brain development during

infancy, the infant’s head must be protected.• Shaken baby syndrome: Damage to brain from

shaking a baby, includes brain swelling and hemorrhaging.


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The Brain: Infancy

• Early Experience and the Brain– Depressed brain activity has been found in children

who grow up in a deprived environment (Cicchetti, 2001), and it’s possible the effects are irreversible.

– Neuroscientists believe that what wires the brain is repeated experience:

• Before birth, genes direct wiring patterns.• After birth sensory and environment input shape

neural connections.


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The Brain: Infancy

Early Deprivation and Brain Activity



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The Brain: Infancy

• Changing Neurons– Myelination, the process of encasing axons with fat

cells, begins prenatally and continues after birth.– Among the most dramatic changes in the brain in the

first 2 years of life are the increases in synaptic connections, with synaptic blooming and pruning.


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The Brain: Infancy

• Changing Structures– The frontal lobe is immature at birth, but increased

myelination and neural connections during the first year enhance the ability to regulate physiological states and gain more control over reflexes.

– 2 months: development of motor control centers allow reaching and grabbing.

– 4 months: neural connections for depth perception begin to form.

– 12 months: speech centers ready to produce language.


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Infancy

The Development of Dendritic Spreading



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The Brain: Infancy

Synaptic Density in the Human Brain from Infancy to Adulthood



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The Brain: Childhood– Brain growth is slower than in infancy, but the brain

and the head grow faster than other parts of the body.• Increase, due to myelination (which is not complete

until the end of middle or late childhood), in number and size of dendrites.

• Most rapid growth from age 3 to 6 is in frontal lobe areas (planning and organizing new actions and maintaining attention to tasks).

• Most rapid growth from age 6 through puberty is in temporal and parietal lobes, especially for language and spatial relations.


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The Brain: Adolescence• Adolescents process emotional information primarily in the

amygdala (emotion-processing area) rather than in the frontal lobe (higher-level reasoning and thinking area); the reverse occurs in adults.

• The adolescent prefrontal cortex is not yet developed to control strong emotions (Nelson, 2003).

• Areas of the limbic system involved with reward and pleasure lead adolescents to seek novelty and to need higher levels of stimulation to experience pleasure.

• Slow development of prefrontal cortex means a lack of cognitive skill for controlling pleasure seeking, which may explain increased risk-taking and other problems.


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• Describe how the brain changes– Review

• What is the nature of brain physiology?• How does the brain change in infancy?• What characterizes the development of the brain in

childhood?• How does the brain change in adolescence and how

might this change be linked to adolescent behavior?


Slide 43


• Reflect– Claims are made that elementary and secondary

education should be brain-based. Some journalists suggest that educators look to neuroscientists for answers about how best to teach children and adolescents. Such statements are speculative and far removed from what neuroscientists know. Find an article on brain-based education in a magazine or on the Internet. Use your critical thinking skills to evaluate the article’s credibility. Does the author present research evidence to support the link between neuroscience and the brain-based method being recommended? Explain.


Slide 44

Sleep

• Sleep restores, replenishes, and rebuilds the brain and body.

• Some neuroscientists believe that sleep allows neurons that have been used during waking to shut down and repair themselves.


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Sleep: Infancy

– Newborns sleep 16 to 17 hours a day, although some sleep more and others sleep less.

– By age 1 month most infants sleep longer at night.– By age 4 months their patterns are closer to adult sleep

patterns.– There are cultural variations in sleep patterns.


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Sleep: Infancy

– REM Sleep• Adults spend about one-fifth of their night in REM

sleep and it usually appears about 1 hour after non-REM sleep.

• About one-half of an infant’s sleep is REM sleep, and infants often begin their sleep cycle with REM sleep rather than non-REM sleep.

• REM sleep might promote the brain’s development in infancy.


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Sleep: Infancy

Sleep Across the Human Life Span



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Sleep: Infancy

– Shared Sleeping• Sharing a bed with a mother is a common practice in

many cultures.• Shared sleeping remains a controversial issue.


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Sleep: Infancy

– SIDS• Sudden infant death syndrome (SIDS)—A

condition that occurs when an infant stops breathing, usually during the night, and suddenly dies without an apparent cause.

• SIDS decreases when infants sleep on their backs.• Risk factors include low birth weight, a sibling who

has died of SIDS, sleep apnea, being African American or Eskimo, lower socioeconomic status, exposure to cigarette smoking, and soft bedding.


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Sleep: Childhood

– Most young children sleep through the night and have one daytime nap, although they may try to drag out their bedtime routine.

– Sixth-graders go to bed an hour later than second-graders and report more daytime sleepiness.

– Sleep problems: Nightmares (frightening dreams that awaken the sleeper) and night terrors (sudden arousal from sleep with intense fear and physiological reactions) are common sleep problems.


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Sleep: Adolescence• Adolescents sleep an average of 9 hours and 25 minutes

when allowed to sleep as long as they like, but most get much less sleep, which creates sleep debt.

• Older adolescents are sleepier than younger adolescents due to hormonal phase shift of biological clocks.

• Melatonin, a hormone that prepares the body for sleep, is secreted an hour later in older adolescents than in younger adolescents.

• Starting school an hour later has improved tests scores and decreased discipline problems, illness, and depression for students in Edina, MN.


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• Summarize how sleep patterns change as people develop– Review

• How can sleep be characterized in infancy?• What changes occur in sleep during childhood?• How does adolescence affect sleep?


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– Reflect• Did your sleep patterns start to change when you

became an adolescent? Have they changed since you went through puberty? If so, how?


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Health

• Illnesses and Injuries among Children and Adolescents– Early Childhood:

• Vaccines have nearly eradicated many diseases.• Birth defects, cancer, and heart disease are the disorders

that are most likely to be fatal to children under age 5 today.

• Accidents are the leading cause of death in young children.

• Parental smoking puts children at risk for respiratory problems and vitamin C deficiency.


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Health

Main Causes of Death in Children 1 Through 4 Years of Age



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Health

• Illnesses and Injuries among Children and Adolescents (continued)– Middle and Late Childhood:

• Mostly a time of excellent health.• Motor vehicle accidents are the most common cause

of severe injury and death; this can be reduced by use of seat belts.

• Cancer is the second leading cause of death for this age group.


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Health

• Illnesses and Injuries among Children and Adolescents (continued)– Adolescence:

• Leading cause of death is accidents, with alcohol involved in 50% of motor vehicle fatalities.

• Homicide is second leading cause of death, and suicide is third.


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Health

• Health, Illness, and Poverty among the World’s Children– 17% of children in the U.S. live in poverty, and 7%

have no source of routine health care.– Lead is linked to lower intelligence and achievement,

and to ADHD.


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Health

• Health, Illness, and Poverty Among the World’s Children (continued)– The poor are a majority in 20% of the world nations.– A leading cause of child death in impoverished

countries is diarrhea produced by dehydration; immunization programs help reduce death by measles, tetanus, and whooping cough.

– HIV/AIDS has dramatically increased for these children and is a major cause of death.


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Health

• Nutrition and Eating Behavior: Infancy– The importance of adequate energy and nutrient intake

consumed in a loving and supportive environment during the infant years cannot be overstated (Samour, Helm, & Lang, 2000).

– Breast-feeding versus bottle-feeding: Benefits include appropriate weight gain, fewer allergies, prevention and reduction of diseases, denser bones in childhood and adulthood, reduced childhood cancer, lower incidence of SIDS, and better visual acuity.


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Health

• Nutrition and Eating Behavior: Infancy– Breast-feeding versus Bottle-feeding

• Avoid breast-feeding when the mother has AIDS, tuberculosis, or is taking a drug that might not be safe for the infant.


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Health

Trends in Breastfeeding in the United States: 1970–2001



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Health

• Nutrition and Eating Behavior: Infancy– Malnutrition in Infancy

• Marasmus: A wasting away of body tissues in the infant’s first year, caused by severe protein-calorie deficiency.

• Kwashiorkor: A condition caused by a deficiency in protein in which the child’s abdomen and feet become swollen with water.

• The effects of nutrition in infancy extend at least into early childhood


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Health

• Nutrition and Eating Behavior: Childhood• Children in many developing countries face

malnutrition and starvation daily.• In the U.S. 11 million preschool children are

malnourished, putting their health at risk; malnutrition is associated with problem behaviors as they get older.

• Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) provides nutrition and counseling on nutrition to low-income participants.


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Health

• Nutrition and Eating Behavior: Childhood– Health and Unhealthy Eating

• Since the late 1970s, eating habits have shifted from healthy foods to salty snacks, soft drinks, pizza, and to high-fat beef and pork.

• Eating high-fat fast foods damages the heart.


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Health

• Nutrition and Eating Behavior: Childhood – Obesity

• Energy requirements depend on physical activity and basal metabolism rate (BMR).

• American eating trends are producing increasing numbers of overweight children and adults.

• Obesity increases the risk of developing medical and psychological problems.

• Experts recommend combining proper diet with exercise and behavior modification.


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Health

Relation of Being Overweight in Childhood with Being Overweight in Adulthood



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Health

• Nutrition and Eating Behavior: Adolescence• Adolescent girls want to weigh less.• Eating disorders are linked with negative body

disorders, sexual activity, and pubertal transition.• Anorexia nervosa is an eating disorder that

involves the relentless pursuit of thinness through starvation.

• Bulimia nervosa is an eating disorder in which the individual consistently follows a binge-and-purge eating pattern.


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Health

Percentage of Overweight U.S. Adolescent Boys and Girls in Different Ethnic Groups



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Health

• Nutrition and Eating Behavior: Adolescence– Exercise:

• Although exercise is linked with many aspects of physical and mental health, U.S. adolescents exercise less than their counterparts in most other countries.

• As age increases, physical activity decreases.• Television watching is linked with low activity and

obesity.


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Health

Percentage of Children Involved in Daily Physical Education Programs in the United States from 1969 to 1999



Slide 72

Health

• Nutrition and Eating Behavior: Adolescence– Substance Use:

• Cigarette smoking begins in childhood and adolescence, and alcohol abuse begins in high school or college.

• The earlier use begins, the greater the detrimental long-term effects.

• Trends in drug use: Declined in 1980s, increased in 1990s; the U.S. has the highest rate of adolescent drug use of any industrialized nation.


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Health

Trends in Drug Use by U.S. Eighth-, Tenth-, and Twelfth-Grade Students



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Health

• Nutrition and Eating Behavior: Adolescence– Substance Use (continued)

• Alcohol use has declined over the past 10 years.• Cigarette smoking is also decreasing; smoking in

adolescence causes permanent genetic changes in the lungs.

• Parents and peers play important roles in preventing adolescent drug abuse.


Slide 75


• Characterize health in childhood and adolescence– Review

• What are the key health problems facing children?• What are some important aspects of children’s

nutrition and eating behavior?• What role does exercise play in children’s

development?• What is the nature of substance use in adolescence?


Slide 76


– Reflect• What were your eating habits like as a child? In

what ways are they similar to or different from your current eating habits? Were your early eating habits a forerunner of whether or not you have weight problems today?


Slide 77

Summary• The cephalocaudal pattern is the sequence in which the

greatest growth occurs at the top—the head—and gradually proceeds from top to bottom.

• The proximodistal pattern is the sequence in which growth starts at the center of the body and moves toward the extremities.

• Height and weight increase rapidly in infancy, then take a slower course in childhood.

• Puberty is a rapid maturation involving hormonal and body changes that occur primarily in early adolescence.


Slide 78

Summary• Each hemisphere of the brain has four lobes (frontal,

occipital, temporal, and parietal).• Communication between neurons occurs through the release

of neurotransmitters.• Myelination begins prenatally and continues after birth, with

enormous increase in synaptic connections during infancy.• During early childhood, the brain and head grow more

rapidly than other parts of the body.• Later development of frontal lobes and earlier dominance of

the amygdala play an important role in adolescent risk-taking behavior.


Slide 79

Summary

• Newborns sleep 16 to 17 hours a day; by 4 months most infants have sleep patterns similar to adults.

• Infants have more REM sleep than older children and adults.

• Sleeping arrangements vary across cultures.• Young children sleep through the night and have a

daytime nap.• Adolescent sleep patterns change due to hormonal

changes that shift their biological clocks.


Slide 80

Summary• In recent decades, vaccines have eradicated many

diseases.• Today the most fatal childhood disorders are birth

defects, cancer, and heart disease.• Accidents are the number one cause of death in

young children.• The leading causes of death for adolescents are

accidents, homicide, and suicide.• Poverty affects the health of children around the

world.


Slide 81

Summary

• Diarrhea caused by dehydration is a major cause of death for children in poor countries, and HIV/AIDS has increased for those children dramatically.

• Adequate energy intake is critical for infants, and breast-feeding is usually recommended over bottle-feeding.

• Marasmus and kwashiorkor are diseases caused by severe malnutrition.


Slide 82

Summary

• Nutritional concerns for children focus on fat content and obesity, with more than 20% of U.S. children being overweight and 10% being obese.

• Obesity increases risks for medical and psychological problems.

• In adolescence, nutrition and being overweight are problems, as are anorexia nervosa and bulimia nervosa.


Slide 83

Summary

• Most children and adolescents in the U.S. do not get enough exercise.

• The U.S. has the highest rate of adolescent drug use of any industrialized nation, and special concerns are alcohol and cigarette smoking.

• Parents and peers play important roles in preventing drug abuse in adolescents.

Documents

5—Physical Development in Infancy