Physical Development Chapter 6

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

Changes in Body Size Rapid changes during infancy 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 Slows in early and middle childhood Sharp acceleration in puberty 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 Different rates Cephalocaudal Cephalocaudal Proximodistal Proximodistal Exceptions to growth trends in adolescence Exceptions to growth trends in adolescence

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

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

Changes in Body Composition Girls more body fat at birth – increases Girls more body fat at birth – increases Around 8, changes begin through puberty for girls Around 8, changes begin through puberty for girls Opposite happens for boys Opposite happens for boys

Changes in Body Composition Muscle different rate than fat Muscle different rate than fat Infancy/childhood  slow Infancy/childhood  slow Adolescence  rises Adolescence  rises In children, muscle composes 18-24% of body weight for both males and females 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 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 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 Different rates Skeletal age Skeletal age Embryonic skeleton  cartilage Embryonic skeleton  cartilage Beginning at 6 th week of pregnancy, bones harden (ossify) – process continues throughout childhood and adolescence Beginning at 6 th week of pregnancy, bones harden (ossify) – process continues throughout childhood and adolescence

Skeletal Development Skull  fontanelles and sutures Skull  fontanelles and sutures Ankles, feet, wrists, hands develop more bones Ankles, feet, wrists, hands develop more bones

Individual and Cultural Differences Most differences within normal range Most differences within normal range Children at extremes Children at extremes What accounts for differences in growth? What accounts for differences in growth? Secular trends in physical growth Secular trends in physical growth

Individual and Cultural Differences May be due to improved nutrition and health 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 billion neurons billion neurons Neural tube of embryo Neural tube of embryo Migrate and differentiate Migrate and differentiate By end of second trimester, most neurons are formed By end of second trimester, most neurons are formed –Produce neurons? –Brain can compensate

Development of the Brain Synaptogenesis Synaptogenesis –Infants more connections than adults –Neurons in synapse get crowded and die Neurons need stimulation to survive 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? If most neurons are produced prenatally, what accounts for increase in size of brain? –Glial cells –Myelinization

Development of the Brain Cerebral Cortex Cerebral Cortex –Largest structure –Responsible for intelligence –Order of development

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

Development of the Brain Lateralization 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 Sequence of motor skills same Large individual variation Large individual variation Rate of motor development ≠ future development outcomes Rate of motor development ≠ future development outcomes

Motor Development Gross motor development Gross motor development Fine 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 Not a series of isolated, unrelated accomplishments Cross-cultural research Cross-cultural research

Motor Development Beyond Infancy: Motor Development in Childhood and Adolescence 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 Physical changes  endocrine system Hormones Hormones Pituitary gland Pituitary gland Growth hormone (GH) Growth hormone (GH)

Hormonal Influences on Physical Growth GH  body tissues except CNS and genitals GH  body tissues except CNS and genitals No prenatal growth, essential from birth on No prenatal growth, essential from birth on Lack GH  average mature height of 4 feet 4 inches Lack GH  average mature height of 4 feet 4 inches Catch-up growth Catch-up growth

Hormonal Influences on Physical Growth Sexual maturation  pituitary secretions Sexual maturation  pituitary secretions Estrogens  female hormones Estrogens  female hormones Androgens  male hormones Androgens  male hormones Both in each sex, different amounts 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 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 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 Adrenal androgens Not sure what sets hormonal processes in motion 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 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 Physically mature; produce offspring Changes in physical features related to sexual functioning Changes in physical features related to sexual functioning –Primary sexual characteristics –Secondary sexual characteristics

Puberty Boys 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 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 Advantages of maturing early and the disadvantages of maturing late are greater for boys than for girls

Heredity vs. Environment Heredity  hormones Heredity  hormones Nutrition Nutrition –Dietary diseases  Marasmus  Kwashiorkor Infectious disease Infectious disease

Heredity vs. Environment Emotional Well-Being Emotional Well-Being –Nonorganic failure to thrive –Deprivation dwarfism