Physical Development

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Physical Development

• Chapter 6

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• Prolonged period of physical growth
• Period between birth/puberty mice/rats (2 of
  lifespan)
• 7 years in chimpanzees (17 of lifespan)
• 20 of total years to growth
• Why?

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Changes in Body Size

• Rapid changes during infancy
• By end of first year, height 50 greater than
  birth
• End of second year, 75 greater
• Weight shows similar gains
• If rate maintained, children would be 10 feet
  tall and weigh over 200 pounds by age 10 12 feet
  tall and weigh several tons by age 18

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Changes in Body Size

• Slows in early and middle childhood
• Sharp acceleration in puberty

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• Figure 6.1 Gain in height per year by males and
  females from birth through adolescence. At age
  10 ½ , girls begin their growth spurt. Boys
  follow some 2 ½ years later and grow faster than
  girls once their growth begins. BASED ON TANNER,
  WHITEHOUSE, TAKAISHI, 1966.

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Changes in Body Proportions

• Different rates
• Cephalocaudal
• Proximodistal
• Exceptions to growth trends in adolescence

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Changes in Body Proportions

• Body proportions similar in infancy and childhood
• Major differences occur during adolescence

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Changes in Body Composition

• Changes in muscle-fat makeup
• Body fat increases pre/postnatally
• Peak 9 months
• Slender starting in second year until middle
  childhood

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Changes in Body Composition

• Girls more body fat at birth increases
• Around 8, changes begin through puberty for girls
• Opposite happens for boys

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Changes in Body Composition

• Muscle different rate than fat
• Infancy/childhood ? slow
• Adolescence ? rises
• In children, muscle composes 18-24 of body
  weight for both males and females
• By their mid-twenties, percent of body that is
  muscle averages 24 for females and about 40 for
  males

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Changes in Body Composition

• Both sexes gain muscle at puberty, gain is
  greater for boys
• Develop larger skeletal muscles
• Larger hearts
• Greater lung capacity
• Number of blood cells increases
• Thus?

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Skeletal Development

• Different rates
• Skeletal age
• Embryonic skeleton ? cartilage
• Beginning at 6th week of pregnancy, bones harden
  (ossify) process continues throughout childhood
  and adolescence

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Skeletal Development

• Skull ? fontanelles and sutures
• Ankles, feet, wrists, hands develop more bones

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Individual and Cultural Differences

• Most differences within normal range
• Children at extremes
• What accounts for differences in growth?
• Secular trends in physical growth

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Individual and Cultural Differences

• May be due to improved nutrition and health
• Orphaned babies from developing countries
• Low-income children
• Regions where poverty, famine, and disease are
  widespread

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Development of the Brain

• 100-200 billion neurons
• Neural tube of embryo
• Migrate and differentiate
• By end of second trimester, most neurons are
  formed
• Produce neurons?
• Brain can compensate

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Development of the Brain

• Synaptogenesis
• Infants more connections than adults
• Neurons in synapse get crowded and die
• Neurons need stimulation to survive
• Synaptic pruning

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Development of the Brain

• If most neurons are produced prenatally, what
  accounts for increase in size of brain?
• Glial cells
• Myelinization

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Development of the Brain

• Cerebral Cortex
• Largest structure
• Responsible for intelligence
• Order of development

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Development of the Brain

• 3-6 ? frontal lobes
• 6-puberty ? temporal and parietal lobes
• MRIs were used to compare brain activity in
  adolescents (10-18) and adults (20-40) while
  processing emotional information

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Development of the Brain

• Lateralization
• When does it occur?
• Tells us about brain plasticity
• Lateralization has already begun at birth
• Lateralization not complete

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Motor Development

• Sequence of motor skills same
• Large individual variation
• Rate of motor development ? future development
  outcomes

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Motor Development

• Gross motor development
• Fine motor development

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• Table 6.1 Age Norms (in Months) for Important
  Motor Developments (Based on European American,
  Latino, and African American Children in the
  United States)

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Motor Development

• Not a series of isolated, unrelated
  accomplishments
• Cross-cultural research

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Motor Development

• Beyond Infancy Motor Development in Childhood
  and Adolescence
• Each year, skills improve
• Large muscles, eye-hand coordination
• Young children ?overestimate
• Puberty males increase in muscle development
  females tend to become less active

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Hormonal Influences on Physical Growth

• Physical changes ? endocrine system
• Hormones
• Pituitary gland
• Growth hormone (GH)

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Hormonal Influences on Physical Growth

• GH ? body tissues except CNS and genitals
• No prenatal growth, essential from birth on
• Lack GH ? average mature height of 4 feet 4
  inches
• Catch-up growth

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Hormonal Influences on Physical Growth

• Sexual maturation ? pituitary secretions
• Estrogens ? female hormones
• Androgens ? male hormones
• Both in each sex, different amounts

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Hormonal Influences on Physical Growth

• Boys testes release large quantities of
  testosterone, which leads to muscle growth, body
  and facial hair, and other male sex
  characteristics, also contributes to gains in
  body size
• Estradiol causes the breasts, uterus, and vagina
  to mature and the body to take on feminine
  proportions, also help regulate menstrual cycle

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Hormonal Influences on Physical Growth

• Adrenal androgens
• Not sure what sets hormonal processes in motion
• Combination of heredity, hormones, and body fat

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• Figure 6.10 Hormonal influences on physical
  development.

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Hormonal Influences on Physical Growth

• In girls, rise in body weight and fat appears to
  play a role in sexual maturation
• Serious athletic training/eat little
• Overweight
• Body fat 17
• Athletes, eating disorders

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Puberty

• Physically mature produce offspring
• Changes in physical features related to sexual
  functioning
• Primary sexual characteristics
• Secondary sexual characteristics

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Puberty

• Boys
• Early maturation advantaged in emotional and
  social functioning (seen as more relaxed,
  independent, self-confident, and physically
  attractive also tend to be more popular, hold
  leadership positions, and are athletic stars)
• Late maturation not well liked (seen as anxious,
  overly talkative, and attention seekers)

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Puberty

• Girls
• Early maturation social difficulties (below
  average in popularity, withdrawn, lack
  self-confidence, hold few positions of
  leadership, more likely to be depressed,
  smoke/drink, have an eating disorder)
• Late maturation physically attractive, lively,
  sociable, leaders at school
• Advantages of maturing early and the
  disadvantages of maturing late are greater for
  boys than for girls

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Heredity vs. Environment

• Heredity ? hormones
• Nutrition
• Dietary diseases
• Marasmus
• Kwashiorkor
• Infectious disease

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Heredity vs. Environment

• Emotional Well-Being
• Nonorganic failure to thrive
• Deprivation dwarfism