Physical Development
Chapter 6
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?

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
Changes in Body Size

Slows in early and middle childhood

Sharp acceleration in puberty
•
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.
Changes in Body Proportions
Different rates
 Cephalocaudal
 Proximodistal
 Exceptions to growth trends in
adolescence

Changes in Body Proportions
Body proportions similar in infancy and
childhood
 Major differences occur during
adolescence

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

Changes in Body Composition
Girls more body fat at birth – increases
 Around 8, changes begin through puberty
for girls
 Opposite happens for boys

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

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…?
Skeletal Development
Different rates
 Skeletal age
 Embryonic skeleton  cartilage
 Beginning at 6th week of pregnancy, bones
harden (ossify) – process continues
throughout childhood and adolescence

Skeletal Development
Skull  fontanelles and sutures
 Ankles, feet, wrists, hands develop more
bones

Individual and Cultural Differences
Most differences within normal range
 Children at extremes
 What accounts for differences in growth?
 Secular trends in physical growth

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
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
Development of the Brain

Synaptogenesis
– Infants more connections than adults
– Neurons in synapse get crowded and die

Neurons need stimulation to survive
– Synaptic pruning
Development of the Brain

If most neurons are produced prenatally,
what accounts for increase in size of
brain?
– Glial cells
– Myelinization
Development of the Brain

Cerebral Cortex
– Largest structure
– Responsible for intelligence
– Order of development
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
Development of the Brain

Lateralization
– When does it occur?
– Tells us about brain plasticity
– Lateralization has already begun at birth
– Lateralization not complete…
Motor Development
Sequence of motor skills same
 Large individual variation
 Rate of motor development ≠ future
development outcomes

Motor Development

Gross motor development

Fine motor development
•
Table 6.1 Age Norms (in Months) for Important Motor Developments (Based on European
American, Latino, and African American Children in the United States)
Motor Development

Not a series of isolated, unrelated
accomplishments

Cross-cultural research
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
Hormonal Influences on Physical
Growth
Physical changes  endocrine system
 Hormones
 Pituitary gland
 Growth hormone (GH)

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

Hormonal Influences on Physical
Growth
Sexual maturation  pituitary secretions
 Estrogens  female hormones
 Androgens  male hormones
 Both in each sex, different amounts

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

Hormonal Influences on Physical
Growth
Adrenal androgens
 Not sure what sets hormonal processes in
motion

– Combination of heredity, hormones, and body
fat
•
Figure 6.10 Hormonal influences on physical development.
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
Puberty
Physically mature; produce offspring
 Changes in physical features related to
sexual functioning

– Primary sexual characteristics
– Secondary sexual characteristics
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)
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
Heredity vs. Environment
Heredity  hormones
 Nutrition

– Dietary diseases
 Marasmus
 Kwashiorkor

Infectious disease
Heredity vs. Environment

Emotional Well-Being
– Nonorganic failure to thrive
– Deprivation dwarfism