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Unformatted text preview: Chapter 3: Physical Growth, Maturation, and Aging Growth and Aging Genetic and extrinsic factors interact and influence growth and aging Universality ~ genetic factors drive orderly and sequenced patterns of development Variability ~ individuals have unique potential and rates of development Important to know both expected patterns and range of variation to make tasks developmentally appropriate Embryonic Development Occurs from conception to 8 weeks # of cells and cells differentiate to form specific tissues and organs Limbs are formed and heartbeat begins at 4 weeks Human form is observable at 8 weeks See Table 3.1 Implantation Fetal Development Occurs from 8 weeks until birth Continued growth leading to functional capacity hyperplasia (increased number of cells) hypertrophy (increased size of cells) Growth proceeds in 2 directions cephalocaudal (head to toe) proximodistal (near to far; body to extremities). There is a degree of plasticity ~ capability of taking on a new function If some cells in a system are injured, the remaining cells might be stimulated to perform the role of the damaged cells Cells of the CNS have high degree of plasticity Assessment of Prenatal Growth Invasive prenatal assessments: Amniocentesis Chorionic villus sampling Noninvasive prenatal assessments: Ultrasound New imaging software constructs 3-D images Brain Development Prenatal Development Prenatal development is under the control of genes Normal development Abnormal development The embryo or fetus can also be influenced by extrinsic factors Positive effects Negative effects Typical Development Fetal Alcohol Syndrome Abnormal development can therefore result from either genetic or extrinsic factors Congenital defects Anomalies present at birth, regardless of whether their causes are genetic or extrinsic Prenatal Development - Genetics Prenatal development is primarily controlled through genetics Normal development Abnormal development Genes can be: Dominant (defective gene from 1 parent) Recessive (defective gene from both parents) X-linked Genetic abnormalities can also result from a new mutation, alteration or deletion of a gene during formation of the egg or sperm cell potential for this increases with advancing maternal age Mutations can also occur spontaneously Effects of genetic abnormalities on growth and maturation are variable Some are obvious at birth, and some abnormalities do not appear until later in postnatal development Prenatal Development Extrinsic Factors Prenatal development is sensitive to extrinsic factors Nourishment ~ diffusion of oxygen, nutrients, and waste products between fetal and maternal blood in the placenta Poor maternal health status can affect the fetus Teratogens ~ any drug or chemical agent that causes abnormal development Effect depends on stage of fetal development when substance is introduced and amount of substance Placenta screens some substances, but not all Pressure applied to mother's abdomen, temperature, exposure to x-rays or gamma rays, oxygen deficiency, pollutants are other potentially harmful environmental factors Postnatal Development Continuation of prenatal growth Predictable and consistent, but not linear Overall growth follows sigmoid pattern (Sshaped) Timing of spurts and steady periods (i.e., rate of growth) likely to vary among individuals Universality vs. Variability Rapid growth after birth, gradual but steady growth during childhood, rapid growth during early adolescence, and then leveling off Timing differs between genders No difference in size at birth Assessment of Postnatal Growth Distance curves show the extent of growth Velocity curves show the rate of growth Peaks on velocity curves show the age at which the rate of growth changes from faster to slower Gender Gender differences minimal in early childhood Girls tend to mature faster than boys Age at Takeoff: age at which the rate of growth begins to increase o Girls are often about 9years old o Boys are on average 11 years old Height Follows the sigmoid pattern Peak Velocity: age at which one is growing the fastest Girls Peak height velocity occurs at 11.5 to 12 years Growth in height plateaus around 14, ends around 16 Boys Peak height velocity occurs at 13.5 to 14 years. Growth in height plateaus around 17, ends around 18 "Rule of Thumb" (Krogman, 1972) Boys: 2 X height at 2 years Girls: 2 X height at 1 years Weight Follows the sigmoid pattern Weight is susceptible to extrinsic factors Diet and exercise Disease can also influence body weight Peak weight velocity follows peak height velocity by 2.5 to 5 months in boys and 3.5 to 10.5 months in girls Individuals grow up and then fill out Relative Growth The body as a whole follows the sigmoid pattern, but specific parts, tissues, and organs have different growth rates Body proportions change from a head-heavy, short-legged form at birth to adult proportions. In adolescence: Boys increase in shoulder breadth Girls shoulder to hip ratio remains relatively constant Physiological Maturation Developmental process leading to a state of full function As children and youths become older, they grow in size and mature Children vary in maturation rate Girls as a group mature earlier than boys It is difficult to infer maturity from age alone, size alone, or age and size together Maturation = age-related (vs age-dependent) Secondary Sex Characteristics Appear as a function of maturation Appear at a younger age in early maturers Girls: Breast growth, pubic hair, menarche (first menstrual cycle) Menarche typically follows the peak height velocity by 11 to 12 months Boys: Testes and scrotum grow in size, pubic hair Maturation Structural Constraint Individuals who are more mature are likely to be stronger and more coordinated than those who are less mature, even at the same chronological age Parents/Educators/Therapists must consider maturation status when designing activities and therapies for youth and when setting performance goals Extrinsic Influence on Postnatal Growth Genetics control the timing and rate of an individual's growth and maturation During periods of rapid growth, individuals are especially sensitive to extrinsic factors Catch-up growth demonstrates extrinsic influences Relatively rapid physical growth of the body to recover some or all of retarded growth during a period of negative extrinsic influence once the negative influence is removed Adulthood and Aging Changes in body size reflect aging of tissues and influence of extrinsic factors Height is stable in adulthood but might decrease in older adulthood Compression of the cartilage pads between the vertebrae Osteoporosis The average adult starts gaining weight in the 20s Diet and exercise Loss of muscle mass Summary Prenatal development is under genetic and extrinsic influences Most extrinsic factors are influential through the nourishment system Growth abnormalities can be caused by the genes, the environment, or both Whole-body growth follows the sigmoid pattern, with timing differences between the sexes and among individuals With advancing age, extrinsic factors contribute more to individual variability Discussion Questions 1. Discuss the differences between measurements of growth and direct measurements of maturation. What does each measure? What are examples of each? - Growth measurements look at the overall growth of the individual -and generally compares to an `average height' for the given age -quantitative measurement of development -example: height and weight measurements -Maturation looks at individual organs, systems, etc... that make up the individual -direct measurements include: -dental eruption (appearance of new teeth, indicated maturation status but is restricted to 2 age spans) -appearance of secondary sex characteristics -assessment of skeletal maturation using X-rays -difference with measuring growth is that early maturers have an older skeletal age than chronological age and late maturers have a younger skeletal age than chronological age 2. What is the difference between a distance curve and a velocity curve? What does each type of curve tell you about growth? Why are peaks in the velocity curve of interest? -Distance curve shows the extent of growth -shape of the curve is sigmoid (increases and levels off) -Velocity curve shows the rate of growth -first derivative of the distance curve -shape of the curve is overall decreasing and is irregular in shape -peaks are of interest because they show the age at which the individual is growing the fastest, and also show when the rate of growth is accelerating and decelerating -peak velocities will also correspond to when children hit puberty -example, in girls, menarche typically follows peak height velocity by about a year 3. What areas of a fetus's body advance first? In what directions does growth proceed? -growth proceeds in a cephalocaudal direction (head to toe) and in a proximodistal direction (body toward the extremities) -i.e. the head and facial structures grow fastest, then the upper body, followed by the lower body (cephalocaudally) -i.e. the trunk first, then the nearest parts of the limbs, and finally the distal parts of the limbs -At 8 weeks, eyes, ears, nose, mouth, fingers and toes are formed -At 12 weeks, the sex is externally recognizable, head is very large for rest of the body 4. Describe how teratogens reach a fetus. What are some of the factors that determine the effect a teratogen has on a fetus? -Teratogens reach the fetus through the exchanges that occur between the maternal and fetal blood via the placenta -effect of teratogen depends on the stage of fetal development, the amount and type of teratogen 5. Describe the gender differences in the course of overall growth from infancy to adulthood. Include the average ages for entering the adolescent growth spurt, peak height velocity, puberty, and the tapering off of growth in height. -Infancy minimal difference -Early childhood boys slightly taller and heavier -Throughout childhood, girls tend to mature at a faster rate than boys -Girls begin adolescent growth spurt at about 9, boys begin at about 11 -Peak height velocity -Girls 11.5 -12 years -Boys 13.5 -14 years -Tapering off of growth -Girls 14-16 -Boys 17-18 6. What body measurements can change in older adulthood? How do they change? -Stature (height) can decrease in older adults -compression and flattening of cartilage pads between the vertebrae compression of spinal column and decrease in trunk length -Bone density -modifications in the protein matrix of the skeleton osteoporosis -Weight loss -inactivity and therefore loss of muscle tissue -also due to loss of appetite 7. Imagine someone who gradually gains 20 pounds between the ages of 20 and 40 years. What could have caused the change? What are the repercussions of the additional weight? -Change could be caused by: -lifestyle changes busy careers and families; don't have the time they used to to exercise, eat properly, etc... sedentary desk job -Repercussions -increased risk for disease high blood pressure, cardiovascular disease, high cholesterol, diabetes ...
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This note was uploaded on 04/18/2008 for the course EDKP 261 taught by Professor Staples during the Fall '07 term at McGill.
- Fall '07