Study Guide for Exam 2 NOTE Exams may contain material not included on this guide Material on guide is not guaranteed to be on exams Use this information as a GUIDE for your studying but do not treat it as a map that will show you everything This information comes from the textbook AND the lectures Chapter 5 Physical Growth Know the main factors that affect physical growth Especially when children are poorly fed ordinary childhood illnesses interact with Extreme emotional deprivation can interfere with the production of GH leading to influence growth by controlling the body s production of and sensitivity to hormones a Especially crucial during the first two years when infants need extra calories to keep their rapidly Heredity Genes process that can be disrupted by mutations Nutrition developing organs functioning properly during a time of rapid brain and body growth Infectious Disease malnutrition in a vicious spiral Emotional Well Being psychosocial dwarfism a growth disorder From book p 176 Compared with other animals primates including humans experience a prolonged period of physical growth Mice and rats develop from birth to puberty in just a few weeks about 2 percent of the lifespan By contrast in chimpanzees the species most similar to humans genetically growth takes about seven years or 16 percent of the lifespan Physical immaturity is even more exaggerated in humans who devote about 20 of their total years to growing This prolonged physical immaturity is adaptive By ensuring that children remain dependent on adults it gives them added time to acquire the knowledge and skills essential for life in a complex social world What gender differences and similarities exist in relation to physical growth plots the average size of a sample of children at each age indicating typical yearly progress Distance Curve toward maturity Growth in height is complete for most North American and European girls by age 16 boys by age 17 During infancy and childhood the two sexes are similar with the typical girl just slightly shorter and lighter Around age 10 to 11 the typical North American and European girl becomes taller and heavier for a time because her pubertal growth spurt takes place two years earlier than the boy s At age 14 however the girl is surpassed by the typical boy whose growth spurt has now started whereas than the typical boy hers is almost finished plots the average amount of growth at each yearly interval revealing the exact timing of growth Velocity Curve spurts Rapid but decelerating growth in infancy A slower constant rate during early and middle childhood A sharp increase in early adolescence followed by a swift decrease as the body approaches its adult size Girls growth spurt is earlier in puberty Changes in Body Proportions In infancy and childhood girls and boys have similar body proportions During adolescence however large differences appear caused by the action of sex hormones on the skeleton Boys shoulders broaden relative to the hips whereas girls hips broaden relative to the shoulders and waist Of course boys also end up considerably larger than girls and their legs are longer in relation to the rest of the body The major reason is that boys have two extra years of preadolescent growth when the legs are growing the fastest Changes in Muscle Fat Makeup At birth girls have slightly more body fat than boys a difference that persists into the early school years and then magnifies Around age 8 girls start to add more fat on their arms legs and trunk they continue to do so throughout puberty while the arm and leg fat of adolescent boys decreases Muscle accumulates slowly throughout infancy and childhood with a dramatic rise at adolescence Both sexes gain muscle at puberty but this increase is 150 greater in boys who develop larger skeletal Also the number of red blood cells and therefore the ability to carry oxygen from the lungs to the muscles Altogether boys gain far more muscle strength than girls contributing to their superior athletic performance muscles hearts and lung capacity increases in boys but not in girls during the teenage years Chart from class PowerPoint Birth Infancy Childhood Adolescence Fat Peaks at 9 months Girls have more From around age 8 girls add more fat on arms legs trunk than boys Girls add Boys lose Muscle Added slowly Added slowly Boys add much more than girls Fat Muscle boys Body fat increases prenatally and also after birth reaching a peak at about 9 months of age Girls have slightly more body fat than boys at birth a difference that persists into the early school years then magnifies increasing throughout puberty Muscle accumulates slowly in infancy and childhood with a dramatic rise in adolescence especially for The number of red blood cells increases in boys but not in girls giving boys greater ability to carry oxygen from the lungs to the muscles and contributing to boys greater muscle strength and superior athletic performance during the teenage years Skeletal Growth Because children of the same age differ in rate of physical growth researchers have devised methods for measuring progress toward physical maturity that are useful for studying the causes and consequences of these individual differences The best estimate of a child s physical maturity is skeletal age a measure of development of the bones of the body and childhood African American children tend to be slightly ahead of Caucasian American children in skeletal age Girls are considerably ahead of boys a gap of about four to six weeks at birth which widens over infancy Girls are advanced in development of other organs as well This greater physical maturity may contribute to girls greater resistance to harmful environmental influences As noted in Chapter 3 girls experience fewer developmental problems than boys and have lower infant and childhood mortality rates Gains in Gross Motor Skills Advances in Early and Middle Childhood Changes in size proportions and muscle strength support an explosion of new gross motor skills As the body becomes more streamlined and less top heavy the center of gravity shifts downward toward the trunk The resulting improvement in balance paves the way for new motor skills involving large muscles From PowerPoint notes Although size and strength contribute to boys superior athletic performance in adolescence in childhood the social environment plays a more prominent role By age 2 preschoolers gaits become smooth and rhythmic secure enough that they
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