chapter 4 Physical Growth, Maturation, and Aging

Growth and Aging Change Individual Constraints Genetic and extrinsic factors combine to influence growth and aging. We observe patterns in growth and aging. Universality: patterns that hold for all humans Specificity: individual variation Educators and therapists can make tasks developmentally appropriate.

Prenatal Development Early development is controlled by genes. Normal development Inherited abnormal development The embryo or fetus is sensitive to extrinsic factors. Positive effects Negative effects

Embryonic Development Conception to 8 weeks Differentiation of cells to form specific tissues and organs Limbs formed at 4 weeks Human form noticeable at 8 weeks

Implantation

Fetal Development 8 weeks to birth Continued growth by hyperplasia (cell number) and hypertrophy (cell size) Cephalocaudal (head to toe) and proximodistal (near to far) Plasticity (capability of taking on a new function)

Fetal Nourishment Oxygen and nutrients diffuse between fetal and maternal blood in placenta. Poor maternal health status can affect fetus.

Abnormal Prenatal Development Source of abnormal development can be genetic or extrinsic. Congenital defects (present at birth) can derive from genetic or extrinsic source.

Genetic Causes of Abnormal Development Can be dominant disorders (defective gene from one parent) or recessive disorders (defective gene from each parent). Can result from mutation of a gene. Effects on growth and maturation are variable. (continued)

Genetic Causes of Abnormal Development (continued) What are some genetic disabilities? What effects does each have on normal growth and development?

Extrinsic Causes of Abnormal Development Extrinsic factors can affect fetus through nourishment or physical environment. Teratogens delivered through nourishment system act as malformation-producing agents. Some teratogenic effects result from too much of a substance, some from too little. (continued)

Extrinsic Causes of Abnormal Development (continued) Placenta screens some substances (e.g., large viruses) but not all harmful ones. Harmful environmental factors include pressure, temperature, X and gamma rays, oxygen-deficient atmospheres, pollutants. Tissues undergoing rapid development at time of exposure are most vulnerable.

Teratogens What are some substances pregnant women are told to avoid? What environments or situations are pregnant women encouraged to avoid? (Hint: consider doctor and dentist offices.) What substances or supplements are women encouraged to take during pregnancy?

Postnatal Development Overall growth follows sigmoid (S-shaped) pattern. Timing of spurts and steady periods can vary between individuals. Timing differs between the sexes.

Height Follows sigmoid pattern. Girls Boys Peak height velocity occurs at 11.5 to 12 years. Growth in height tapers off around 14, ends around 16. Boys Peak height velocity occurs at 13.5 to 14 years. Growth in height tapers off around 17, ends around 18. Long growth period of males contributes to absolute height differences.

Velocity Curves for Height

Individual Variation Average ages for peak height velocity and tapering of growth are based on groups. Individuals can differ from the averages. In what ways can individuals vary from the average pattern?

Weight Follows sigmoid pattern. Is susceptible to extrinsic factors, especially diet and exercise. Individuals grow up, then fill out: Peak weight velocity follows peak height velocity (by 2.5–5 months in boys, 3.5–10.5 in girls).

Relative Growth Body as a whole follows sigmoid pattern; specific parts, tissues, and organs have different growth rates. Body proportions change from head-heavy, short-legged form at birth to adult proportions. In adolescence, boys increase in shoulder breadth.

Body Proportions Are adults all of the same proportions? Describe differences in proportion among your friends and acquaintances.

Physiological Maturation As children and youth become older, they grow in size and mature. Children vary in maturation rate. It is difficult to infer maturity from age alone, size alone, or age and size together.

Implications of Maturation Rate How should we counsel parents of an early maturer and star athlete about the child’s future in athletics?

Secondary Sex Characteristics Characteristics appear as a function of maturation. They appear at a younger age in early maturers. Have you seen variations among a group of preteens in appearance of secondary sex characteristics? Which ones?

Extrinsic Influences on Postnatal Growth Individuals are especially sensitive during periods of rapid growth. Catch-up growth demonstrates extrinsic influences. What extrinsic factors are most likely to affect growth during infancy? During the adolescent growth spurt?

Adulthood and Aging Height is stable in adulthood but may decrease in older adulthood. Compression of cartilage pads Osteoporosis Average adult starts gaining weight in the 20s. Diet and exercise Loss of muscle mass

Growth, Maturation, and Aging: Summary Prenatal development is influenced by genetic and extrinsic factors. Most extrinsic factors are influential through the nourishment system. Growth abnormalities can be caused by genes, environment, or both. (continued)

Growth, Maturation, and Aging: Summary (continued) Whole-body growth follows sigmoid pattern (with timing differences between the sexes and between individuals). With advancing age, extrinsic factors contribute more to individual variability.

Assessment of Prenatal Growth Invasive prenatal assessments Amniocentesis Chorionic villus sampling Noninvasive prenatal assessments Ultrasound (most common) 3-D images (using new imaging software) Click to add notes

Assessment of Extent and Rate of Postnatal Growth Distance curves show extent of growth. Velocity curves show rate of growth. Peaks on velocity curves show ages at which rate of growth changes from faster to slower.