Chapter 4 Flashcards
(19 cards)
DESCRIBING GROWTH
height and weight
The growth charts show the average changes in height and weight that take place as children grow from birth to age 20.
- increases in height and weight are not steady. Looking at the average increase in weight and height annually - as opposed to the average total weight and height for each year-gives quite a different picture of the pattern of physical growth.
Between birth and 2 years, for example, average height increases from 19 to 32 inches; average weight increases from 7 to 22 pounds.
boys achieve half their adult height by 2 years, and girls by 18 months.
growth is extraordinarily rapid during the first year, when the average baby gains about 10 inches and 15 pounds. Growth is fairly steady through the preschool and elementary-school years, about 3 inches and 7 to 8 pounds each year. In early adolescence, growth is rapid again. During this growth spurt, which corresponds to the peaks in the middle of the charts
teenagers typically grow 4 inches and gain 16 to 17 pounds each year. After this spurt, which begins 1 to 2 years earlier in girls, growth again slows as children reach adulthood.
As children grow, their body parts develop at different rates, which means that infants and young children are not simply scaled-down versions of adults. The head and trunk grow faster than the legs.
MUSCLE, FAT, AND BONES.
Virtually all of the body’s muscle fibers are present at birth. During childhood, muscles become longer and thicker as individual fibers fuse together. This process accelerates during adolescence, particularly for boys.
A layer of fat appears under the skin near the end of the fetal period of prenatal development; just as insulation in walls stabilizes the temperature inside a house, fat helps the fetus and infant regulate body temperature. Fat continues to accumulate rapidly during the first year after birth, producing the familiar look we call baby fat. During the preschool years, children actually become leaner, but in the early elementary-school years they begin to acquire more fat again. This happens gradually at first, then more rapidly during ado- lescence. The increase in fat in adolescence is more pronounced in girls than in boys.
Bone begins to form during prenatal development. What will become bone starts as cartilage, a soft, flexible tissue. During the embryonic period, the center of the tissue turns to bone. Then, shortly before birth, the ends of the cartilage structures, known as epiphyses, turn to bone. Working from the center, cartilage turns to bone until finally the enlarging center section reaches the epiphyses, ending skeletal growth.
VARIATIONS ON THE AVERAGE PROFILE.
Today, adults and children are taller and heavier than previous generations, due largely to improved health and nutrition. Changes in physical development from one generation to the next are known as secular growth trends.
'’Average’’ physical growth varies not only from one generation to the next, but also from one country to another.
Youngsters from the United States, Western European countries, Japan, and China are about the same height, approximately 49 inches. Children in Africa and India are shorter, averaging just under 46 inches. And 8-year-olds in Polynesia are shorter still, averaging 43 inches.
Many children are much taller or shorter than average and perfectly normal
Mechanisms of Physical Growth
Sleep, nutrition
SLEEP
The amount of time that children spend asleep drops gradually, from roughly 11 hours at age 3 to 10 hours at age 7 and 9 hours at age 12
Sleep is essential for normal growth because about 80% of the hormone that stimulates growth-named, appropriately, growth hormone-is secreted while children and adolescents sleep. Growth hormone is secreted during sleep by the pituitary gland in the brain; from the brain, growth hormone travels to the liver, where it triggers the release of another hormone, somatomedin, which causes muscles and bones to grow
Sleep also affects children’s development in a less direct but no less important manner. Children’s sleep affects their cognitive processes and their adjustment to school.
One way to avoid sleep-related problems in younger children is a bedtime rou- tine that helps them wind down from busy daytime activities. This routine should start at about the same time every night (“It’s time to get ready for bed”) and end at about the same time
Sleep loss can be a particular problem for adolescents. On the one hand, ado- lescents often stay up later at night finishing ever-larger amounts of homework, spending time with friends, or working at a part-time job. On the other hand, adolescents often start school earlier than younger elementary-school students. The re- sult is often a sleepy adolescent who struggles to stay awake during the school day
NUTRITION
In a 2-month-old, roughly 40% of the body’s energy is devoted to growth
young babies must consume an enormous number of calories in relation to their body weight. An adult needs to consume only 15 to 20 calories per pound, depending on level of activity, but a 12-pound. 3-month-old should eat about 50 calories per pound of body weight, or 600 calories.
What’s the Best Food for Babies?
- Breast-feeding is the best way to ensure that babies get the nourishment they need. Human milk contains the proper amounts of carbohydrates, fats, protein, vitamins, and minerals for babies. they are ill less often because a mother’s breast milk contains antibodies that kill bacteria and viruses. Breast-fed babies are less prone to diarrhea and constipation. Breast-fed babies typically make the transition to solid foods more easily. breast milk cannot be contaminated (as long as a nursing mother avoids certain drugs, such as cocaine) j in contrast, contamination is often a significant problem when formula is used in developing countries to bottle-feed babies.
Formula, when prepared in sanitary conditions, provides generally the same nutrients as human milk, but infants are more prone to develop al- lergies from formula, and formula does not protect infants from disease.
In the United States and Canada, newborns and very young babies are often breast-fed exclusively. Beginning at about 4 to 6 months, breast-feeding is supplemented by cereal and strained fruits and vegetables. Strained meats are introduced at 7 to 9 months and finely chopped table foods are introduced at 10 to 12 months
A good rule is to introduce only one new food at a time.
One rule of thumb is that preschoolers should consume about 40 calories per pound of body weight, which works out to be roughly 1,500 to 1,700 calories daily for many children in this age group.
More important than the sheer number of calories, however, is a balanced diet that includes all five major food groups (grains, vegetables, fruits, milk, meat, and beans). A healthy diet also avoids too much sugar and, especially, too much fat.
encouraging children to be more open-minded
about foods and for dealing with them when they aren’t:
* When possible, allow children to pick among different healthy foods (e.g., milk versus yogurt).
* Allow children to eat foods in any order they want.
* Offer children new foods one at a time and in small amounts; encourage but don’t force children to eat new foods.
* Don’t force children to “clean their plates.”
* Don’t spend mealtimes talking about what the child is or is not eating; instead, talk about other topics that interest the child.
* Never use food to reward or punish children.
The Adolescent Growth Spurt and Puberty
For many child-development researchers, adolescence begins officially with puberty, which refers to the adolescent growth spurt and sexual maturation
hysical growth is slow during the elementary-school years: In an average year, a 6- to lO-year-old girl or boy gains about 5 to 7 pounds and grows 2 to 3 inches. But during the peak of the adolescent growth spurt, a girl may gain as many as 20 pounds in a year and a boy, 25
This growth spurt lasts a few years.
girls typically begin their growth spurt about 2 years before boys do. That is, girls typically start the growth spurt at about age 11, reach their peak rate of growth at about 12, and achieve their mature stature at about age 15. In contrast, boys start the growth spurt at 13, hit peak growth at 14, and reach mature stature at 17.
During the growth spurt, bones become longer (which, of course, is why adolescents grow taller) and become more dense.
Muscle fibers become thicker and denser during adolescence, producing substantial increases in strength. However, muscle growth is much more pronounced in boys than in girls
Body fat also increases during adolescence, but much more rapidly in girls than boys. Finally, heart and lung capacities increase more in adolescent boys than in adolescent girls.
Osteoporosis is a disease in which a person’s bones become thin and brittle, and, as a consequence, sometimes break.
- healthy bone growth in adolescence is also an essential defense to fight against this disease
dolescents not only become taller and heavier, but also become mature sexually. Sexual maturation includes change in primary sex characteristics, which refer to organs that are directly involved in reproduction. These include the ovaries, uterus, and vagina in girls and the scrotum, testes, and penis in boys. Sexual maturation also includes change in secondary sex characteristics, which are physical signs of maturity that are not linked directly to the reproductive organs. These include the growth of breasts and the widening of the pelvis in girls, the appearance of facial hair and the broadening of shoulders in boys, and the appearance of body hair and changes in voice and skin in both boys and girls.
For girls, puberty begins with growth of the breasts and the growth spurt, followed by the ap- pearance of pubic hair. Menarche, the onset of menstruation, typically occurs at about age 13
Early menstrual cycles are usually irregular and without ovulation.
For boys, puberty usually commences with the growth of the testes and scrotum, followed by the appearance of pubic hair, the start of the growth spurt, and growth of the penis. At about age 13, most boys reach spermarche, the first spontaneous ejaculation of sperm-laden fluid. Initial ejaculations often contain relatively few sperm; only months or sometimes years later are there sufficient sperm to fertilize an egg
CULTURAL INFLUENCES - Adolescent Rites of Passage
In ancient Japan, for example, a ceremony
was performed for 12- and 14-year-old boys and girls in which they received adult clothing and adult hair styles.
Traditionally, as adolescents, indigenous Australian males walked alone in the wilderness, retracing their ancestors’ paths.
Modern variants of these ceremonies include bar and bat mitzvah, which recognize that young Jewish adolescents are now responsible for their own actions, and Quinceafiera, which celebrates coming of age in I5-year-old girls in many Spanish- speaking regions in North, Central, and South America.
The Western Apache, who live in the southwest portion of the United States, are unusual in having a traditional ceremony to celebrate a girl’s menarche
- After a girl’s first menstrual period, a group of older adults decide when the ceremony will be held and select a sponsor-a woman of good character and wealth (she helps to pay for the ceremony) who is unrelated to the initiate. On the day before the ceremony, the sponsor serves a large feast for the girl and her family; at the end of the ceremony, the family reciprocates, symbolizing that the sponsor is now a member of their family. The ceremony includes eight distinct phases in which the initiate dances or chants, sometimes accompanied by her sponsor or a medicine man.
MECHANISMS OF MATURATION
What causes the many physical changes that occur during puberty? The pituitary gland in the brain is the key player.
the pituitary helps to regulate physical development by releasing growth hormone. In addition, the pituitary regulates pubertal changes by signaling other glands to secrete hormones. During the early elementary-school years, the pituitary signals the adrenal glands to release androgens, initiating the biochemical changes that will produce body hair. A few years later, in girls the pituitary signals the ovaries to release estrogen, which causes the breasts to enlarge, the female genitals to mature, and fat to accumulate. In boys the pituitary signals the testes to release the androgen testosterone, which causes the male genitals to mature and muscle mass to increase.
The timing of pubertal events is regulated, in part, by genetics.
mother’s age at menarche is related to her daughter’s age at menarche
However, these genetic forces are strongly influenced by the environment, particularly an adolescent’s nutrition and health. In general, puberty occurs earlier in adolescents who are well nourished and healthy than in adolescents who are not.
Cross-cultural comparisons reveal that menarche occurs earlier in areas of the world where nutrition and health care are adequate. For example, menarche occurs an average of 2 to 3 years earlier in Western European and North American countries than in African countries. And, within regions, socioeconomic status matters: Girls from affluent homes are more likely to receive adequate nutrition and health care and, consequently, they reach menarche earlier
In many industrialized countries around the world, the average age of menarche has declined steadily over the past 150 years.
- This drop reflects improvements and better health care over this period.
What may surprise you is that the social environment also influences the onset of puberty, at least for girls. Menarche occurs at younger ages in girls who experience chronic stress or who are depressed
A Paternal Investment Theory of Girls’ Pubertal Timing
- According to Ellis, when a girl’s childhood experiences indicate that paternal investment is common and of high quality, this may delay timing of maturation. But when those experiences indicate that paternal investment is uncommon and often of low quality, this may trigger early maturation.
- Puberty was earlier when father-daughter interactions were uncommon or negative, which, according to Ellis, indicates that the environment contains relatively few high-quality fathers
PSYCHOLOGICAL IMPACT OF PUBERTY
For example, compared to children and adults, adolescents are much more concerned about their overall appearance
Maturing early or late has psychological consequences that differ for boys and girls. Several longitudinal studies show that early maturation can be harmful for girls. Girls who mature early often lack self-confidence, are less popular, are more likely to be depressed and have behavior problems, and are more likely to smoke and drink
And early maturation can have life-changing effects on early-maturing girls who are pressured into sex and become mothers while still teenagers: as adults they typically have less prestigious, lower-paying jobs
When early-maturing girls have warm, supportive parents, for example, they are less likely to suffer the consequences of early maturation
Some early studies suggested that early maturation benefits boys.
But other studies have supported the “off-time hypothesis” for boys. In this view, being early or late is stressful for boys, who strongly prefer to be “on time” in their physical development.
Malnutrition
Worldwide, about one in four children under age 5 suffers from malnutrition, as indicated by being small for their age
In fact, nearly half of the world’s undernourished children live in India, Bangladesh, and Pakistan
malnutrition is regrettably common in industrialized countries, too. Many American children growing up homeless and in poverty are malnourished. Approximately 10% of American households do not have adequate food
Children who were malnourished as infants were just as tall and weighed just as much as their peers. However, the children with a history of infant malnutrition had much lower scores on intelligence tests. They also had difficulty maintaining attention in school; they were easily distracted. Malnutrition during rapid periods of growth apparently damages the brain, affecting a child’s intelligence and ability to pay attention
Bad cycle: A biological influence - lethargy stemming from insufficient nourishment - causes a profound change in the experiences - parental teaching - that shape a child’s development
SHORT-TERM HUNGER.
- Breakfast should provide about one-fourth of a child’s daily calories. Yet, many children-in developed and developing countries-do not eat breakfast
- When children don’t eat breakfast, they often have difficulty paying attention or remembering in school
- One strategy to attack this problem is to provide free and reduced-price meals for children at school. Lunch programs are the most common, but breakfast and dinner are sometimes available, too.
Eating Disorders: Anorexia and Bulimia
Anorexia nervosa is a disorder marked by a persistent refusal to eat and an irrational fear of being overweight.
- Anorexia is a very serious disorder, often leading to heart damage. Without treatment, as many as 15% of adolescents with anorexia die
Individuals with bulimia nervosa alternate between binge eating periods when they eat uncontrollably and purging through self-induced vomiting or with laxatives.
Anorexia and bulimia are alike in many respects. Both disorders primarily affect females and emerge in adolescence
- many of the same factors put teenage girls at risk for both eating disorders
- heredity puts some girls at risk, and molecular genetic studies have implicated genes that regulate both anxiety and food intake
- when kids have history of eating problems, such as being a picky eater or being diagnosed with pica (i.e., eating nonfood objects such as chalk, paper, or dirt), they’re at greater risk for anorexia and bulimia during adolescence.
- Teenagers who experience negative self-esteem or mood or anxiety disorders are at risk. However, the most important risk factor for adolescents is being overly concerned about one’s body and weight and having a history of dieting.
Although eating disorders are more common in girls, boys make up about 10% of diagnosed cases of eating disorders.
Obesity
The technical definition for overweight is based on the body mass index (BMI), which is an adjusted ratio of weight to height. Children and adolescents who are in the upper 5% (very heavy for their height) are defined as being overweight.
In the past 25 to 30 years, the number of overweight children has doubled and the number of overweight adolescents has tripled, so that today roughly one child or adolescent out of seven is overweight
Heredity plays an important role in juvenile obesity
- Genes may influence obesity by influencing a
person’s activity level. In other words, being genetically more prone to inactivity makes it more difficult to burn off calories and easier to gain weight.
- Heredity may also help set basal metabolic rate, the speed at which the body consumes calories. Children and adolescents with a
slower basal metabolic rate burn off calories less rapidly, making it easier for them to gain weight
The environment is also influential. Television advertising, parents, etc.
Obese youth can lose weight. The most effective weight-loss programs have several features in common:
* The focus of the program is to change obese children’s eating habits, encourage them to become more active, and discourage sedentary behavior.
* As part of the treatment, children learn to monitor their eating, exercise, and sedentary behavior. Goals are established in each area, and rewards are earned when the goals are met.
* Parents are trained to help children set realistic goals and to use behavioral principles to help children meet these goals. Parents also monitor their own lifestyles to be sure they aren’t accidentally fostering their child’s obesity.
- only 20% of these programs work, the remaining 80% were ineffective
Disease
Around the world more than 10 million children die before their fifth birthday.
The leading killers of young children worldwide are five conditions: pneumonia, diarrhea, measles, malaria, and malnutrition
- most preventable
World Health Organization (WHO) has worked to vaccinate children worldwide. Due to these efforts, vaccination rates have skyrocketed in many developing countries. More recently, WHO has joined with the United Nations Children’s Fund (UNICEF) to create Integrated Management of Childhood Illness (IMCI), a program to combat pneumonia, diarrhea, measles, malaria, and malnutrition (World Health Organization, 1997)
One component of IMCI is training health care professionals to become more skilled in dealing with childhood illnesses. A second component is improving health care systems so that they are better able to respond to childhood illness. A third component involves changing family and community practices to make them more conducive to healthy growth.
Accidents
n the United States, most infant deaths are due to medical conditions associated with birth defects or low birth weight. From age 1, however, children are far more likely to die from accidents than from any other single cause
Motor vehicle accidents are the most common cause of accidental death in children.
Many infants and toddlers also drown, die from burns, or suffocate.
Some accidents happen because parents have too much confidence in their children’s cognitive and motor skills.
For adolescents, motor vehicle accidents remain the leading cause of death. The difference, of course, is that adolescents are no longer passengers but are driving. And, sadly, far too many adolescents are killed because they drive too fast, drive while drunk, and drive without wearing a seat belt
Among teenage boys, firearms represent a leading cause of death. In fact, firearms kill more 15- to 19-year-old African American youth than any other single cause
Organization of the Mature Brain
The basic unit of the brain and the rest of the nervous system is the neuron, a cell that specializes in receiving and transmitting information.
he cell body at the center of the neuron contains the basic biological machinery that keeps the neuron alive. The receiving end of the neuron, the dendrite, looks like a tree with many branches.
The tube- like structure at the other end of the cell body is the axon, which sends information to other neurons. The axon is wrapped in myelin, a fatty sheath that allows it to transmit information more rapidly.
At the end of the axon are small knobs called terminal buttons, which release neurotransmitters, chemicals that carry information to nearby neurons. Finally, you’ll see that the terminal buttons of one axon don’t actually touch the dendrites of other neurons.
The gap between one neuron and the next is a synapse.
Take 50 to 100 billion neurons like these and you have the beginnings of a human brain. An adult’s brain weighs a little less than 3 pounds, and it easily fits into your hands. The
wrinkled surface of the brain is the cerebral cortex; made up of about 10 billion neurons, the cortex regulates many of the functions that we think of as distinctly human. The cortex consists of left and right halves, called hemispheres, that are linked by millions of axons in a thick bundle called
the corpus callosum.
Personality and your ability to make and carry out plans are largely functions of an area at the front of the cortex that is called, appropriately, the frontal cortex.
the ability to produce and understand language, to reason, and to compute is largely due to neurons in the cortex of the left hemisphere. Also for most people, artistic and musical abilities, perception of spatial relations, and the ability to recognize faces and emotions come from neurons in the right hemisphere.
EMERGING BRAIN STRUCTURES.
At roughly 3 weeks after conception, a group of cells form a flat structure known as the neural plate. At 4 weeks, the neural plate folds to form a tube that ultimately becomes the brain and spinal cord. When the ends of the tube fuse shut, neurons are produced in one small region of the neural tube. Production of neurons begins about 10 weeks after conception, and by 28 weeks the developing brain has virtually all the neurons it will ever have.
From the neuron-manufacturing site in the neural tube, neurons migrate to their final positions in the brain. The brain is built in stages, beginning with the innermost layers. Neurons in the deepest layer are positioned first, followed by neurons in the second layer, and so on. This layering process continues until all six layers of the mature brain are in place, which occurs about 7 months after conception
In the 4th month of prenatal development, axons begin to acquire myelin- the fatty wrap that speeds neural transmission. This process continues through infancy and into childhood and adolescence
- You can see the effect of more myelin in improved coordination and reaction times. The older the infant and, later, the child, the more rapid and coordinated are his or her reactions.
In the months after birth, the brain grows rapidly. Axons and dendrites grow longer, and, like a maturing tree, dendrites quickly sprout new limbs.
- As the number of dendrites increases, so does the number of synapses, reaching a peak at about the first birthday
- Soon after, synapses begin to disappear gradually, a phenomenon known as synaptic pruning. Thus, beginning in infancy and continuing into early adolescence, the brain goes through its own version of “downsizing;’ weeding out unnecessary connections between neurons.
- Pruning is completed first for brain regions associated with sensory and motor functions. Re- gions associated with basic language and spatial skills are completed next, followed by regions associ- ated with attention and planning
STRUCTURE AND FUNCTION of brain
different methods to map functions onto particular brain regions
- Studies of children with brain damage
- Studies of electrical activity: Metal electrodes placed on an infant’s scalp, as shown in the top photo, produce an electroencephalogram (EEG), a pattern of brain waves.
- Studies using imaging techniques: Functional magnetic resonance imaging (f-MRI) uses magnetic fields to track the flow of blood in the brain.
None of these methods is perfect; each has drawbacks. In cases of brain injury, for example, multiple areas of the brain may be damaged, making it hard to link impaired functioning to a particular brain region. fMRI is used sparingly because it’s very expensive and participants must lie still for several minutes at a time.
EEG studies show that a new-born infant’s left hemisphere generates more electrical activity in response to speech than the right hemisphere
Right-Hemisphere Specialization for Face Processing
BRAIN PLASTICITY AND THE ROLE OF ENVIRONMENTAL INPUT.
Plasticity refers to the extent to which brain organization is flexible.
Neurons can take over language-related processing from the damaged neurons. This recovery of function is not uncommon, particularly for young children, and shows that the brain is plastic. In other words, young children often recover more skills after brain injury than older children and adults, apparently because functions are more easily reassigned in the young brain
However, the brain is not completely plastic-brains have a similar structure and similar mapping of functions on those structures. The visual cortex, for example, is always near the back of the brain. The sensory cortex and motor cortex always run across the middle of the brain.
The human brain IS plastic, its organization and function can be affected by experience
emphasize the role of environmental stimulation in normal brain development.
In this case, environmental input influences experience-expectant growth-over the course of evolution, human infants have typically been exposed to some forms of stimulation that are used to adjust brain wiring, strengthening some circuits and eliminating others.
Experience-dependent growth denotes changes in the brain that are not linked to specific points in development and that vary across individuals and across cultures.
