case study human growth and development

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StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-.

StatPearls [Internet].

Human growth and development.

Palanikumar Balasundaram ; Indirapriya Darshini Avulakunta .

Affiliations

Last Update: March 8, 2023 .

• Continuing Education Activity

Evaluation of growth and development is a crucial element in the physical examination of a patient. A piece of good working knowledge and the skill to evaluate growth and development are necessary for any patient's diagnostic workup. The early recognition of growth or developmental failure helps for effective intervention in managing a patient's problem. This activity reviews the various aspects of human growth and development and highlights the interprofessional team's role in assessing the kids for growth and developmental delay.

• Describe the stages of growth and development.
• Review the factors affecting growth and development.
• Outline the methods for growth measurements and standard screening tools for developmental assessment.
• Explain how interprofessional collaboration and communication can improve patient outcomes when assessing a patient's physical development.
• Introduction

In the context of childhood development, growth is defined as an irreversible constant increase in size, and development is defined as growth in psychomotor capacity. Both processes are highly dependent on genetic, nutritional, and environmental factors.  Evaluation of growth and development is a crucial element in the physical examination of a patient. A piece of good working knowledge and the skills to evaluate growth and development are necessary for any patient's diagnostic workup. The early recognition of growth or developmental failure helps for effective intervention in managing a patient's problem.

Stages in Human Growth and Development 

• Fetal stage: Fetal health issues can have detrimental effects on postnatal growth. One-third of neonates with intrauterine growth retardation might have curtailed postnatal growth. [1]  Good perinatal care is an essential factor in promoting fetal health and indirectly postnatal growth.
• Infancy (neonate and up to one year age)
• Toddler ( one to five years of age)
• Childhood (three to eleven years old) - early childhood is from three to eight years old, and middle childhood is from nine to eleven years old. 
• Adolescence or teenage (from 12 to 18 years old)

Factors Affecting Growth and Development 

The growth and development are positively influenced by factors, like parental health and genetic composition, even before conception. [3]

• Genetic factors play a primary role in growth and development. The genetic factors influencing height is substantial in the adolescence phase. [4]  A large longitudinal cohort study of 7755 Dutch twin pairs has suggested that the additive genetic factors predominantly explained the phenotypic correlations across the ages for height and body mass index. [5]  
• Fetal health has a highly influential role in achieving growth and development. Any stimulus or insult during fetal development causes developmental adaptations that produce permanent changes in the latter part of life.
• After birth, the environmental factors may exert either a beneficial or detrimental effect on growth. [6]
• Socioeconomic factors: Children of higher socio-economical classes are taller than the children of the same age and sex in the lower socioeconomic groups. Urbanization has positively influenced growth. The secular trend is observed in growth where the kids grow taller and mature more rapidly than the previous generation. This secular trend is observed significantly in developed countries like North America.
• The family characteristics: Higher family education levels have a positive impact on growth. The inadequate emotional support and inadequate developmental stimulus, including language training, might cause growth and development deterioration. 
• The human-made environment influences human growth and development significantly. Certain ongoing studies have proven the relationship of pollutants in sexual maturation, obesity, and thyroid function. [7]  The excess lead exposure antenatally significantly associates with low birth weight. Noise pollution due to transportation sources also has an association with reduced prenatal growth. 
• Nutrition  
• Malnutrition plays a detrimental role in the process of growth and development. 
• Deficiencies of trace minerals can affect growth and development. [8]  Iron deficiency usually affects psychomotor development and does not affect growth. Zinc deficiency might cause growth retardation and developmental delay. Selenium, iodine, manganese, and copper also play a significant role. 
• Growth faltering or rapid weight gain in early childhood influences health in the later part of life. The diet in early childhood has a strong association with the likelihood of obesity later in life. 'Early Protein Hypothesis' shows that lowering the protein supply during infancy helps achieve normal growth and reduce obesity in early childhood. [9]  This concept of the early protein hypothesis helps in improving the food products for children. 
• Genetic and environmental factors influence the growth and development in a perplexing interrelated pathway. Genetic and environmental risk factors are not mutually exclusive. Plasticity is the potential of a specific genotype to bring out diversified phenotypes in response to diverse environmental factors. [10]  The developmental plasticity can happen from the embryonic stage to adolescence and can be passed onto the next generation. 
• Role of experience during early childhood: Exposure to adverse experiences in early childhood might hinder development. Profound neglect during early childhood can impair development. Children adopted before six months of age have similar development when compared to their non-adoptive siblings. If children adopted after six months have a high risk of cognition deficits, behavioral issues, autism, and hyperactivity. [11]  Early intervention for children with adverse experiences is the pillar in healthy development.
• Issues of Concern

Measurement of Growth

Anthropometry is the gold standard by which clinicians can assess nutritional status. The major anthropometric measurements for age up to 2 years are weight, length, weight for length, and head circumference. The major measurements used for children above two years are weight, height, body mass index (BMI), and head circumference for the 2-3 years age group. 

• Length or height:  For children less than two years or children with severe cerebral palsy, the length is the ideal way of measuring stature. Length is measured by placing the child supine on an infant measuring board. For children aged more than two years, standing height is measured in the stadiometer after removing shoes. The supine length is usually 1 cm higher than standing height. Length and height can be documented to the closest 0.1 cm. For children with severe cerebral palsy or spinal deformities, upper arm length, tibial length, and knee height can be useful to assess stature. [12]
• Weight:  The kids below one year are weighed on a scale after removing the clothes, shoes, diaper, and documented to the closest 0.01 kg. The kids outside the infancy phase should be measured without shoes, with little or no outer clothing, and documented to the closest 0.1 kg. 
• Head circumference or occipitofrontal circumference:  Head circumference is assessed by measuring the largest area from the prominent site at the back (occiput) to the frontal prominence above the supraorbital ridge. Brain growth is maximum in the first three years of life, so head circumference is used in children less than three years.  It is measured as the maximum diameter through the supraorbital ridge to the occiput and documented to the closest 0.01 cm. Microcephaly is more than two standard deviations below the mean. Macrocephaly is more than two standard deviations above the mean. 
• < 5th percentile - underweight 
• 5th to 84th percentile - normal 
• 85th to 95th percentile - overweight 
• 95th to 98th percentile - obesity 
• More than 99th percentile - severe obesity
• The weight to length ratio is an alternative for body mass index in predicting adiposity in less than two years. 
• Self-assessment of the hip to waist ratio can help to guide the measure of central adiposity,
• Triceps and subscapular skinfolds can also be a useful measure of adiposity. [13]
• The upper segment to lower segment (U/L) ratio is 1.7 at birth, 1.3 at three years, and reaches 1.0 at greater than seven years. A higher U/L ratio is a feature in short-limb dwarfism.
• Arm span to height ratio is a fixed ratio across all ages. The ratio of more than 1.05:1 is suggestive of Marfan syndrome. [14]
• Sexual maturity:  Tanner's stage can be used to assess sexual maturity.
• Skeletal maturity:  Bone age can be determined by doing Hand & Wrist radiographs from 3 to 18 years of age. 
• Dental assessment:  Primary tooth eruption begins with the central incisors at six months. No single tooth by 13 months of age is of concern. Permanent tooth eruption starts at six years of age and continues up to 18 years of age. 

Growth Velocity 

The growth velocity is different at different stages of life. Also, different tissues grow at different rates at the same stage of life. The lymphoid tissues can exceed adult size at six years of age. Girls are taller than boys at 12 to 14 years, but later they will not grow taller than their boy's counterpart. Growth velocity is maximum during infancy and adolescence. The head circumference reaches closer to adult size by six years of age. The prepubertal height velocity of less than 4 cm per year is of concern. During puberty, the height velocity is 10 to 12 cm per year in boys and 8 to 10 cm per year in girls. The prepubertal weight velocity of less than 1 kg per year is of concern. Weight velocity is highest during puberty, up to 8 kg per year.

Stages of Development

Development is a continuous process from neonatal to adulthood. Though the growth ceases after adolescence, adolescence is not the end for development. Each developmental stage has a new set of challenges and opportunities. 

• Infancy : Development progress in cephalo-caudal direction and also from the midline to the lateral direction.  A three to four-month variation can be there in achieving the developmental milestone. Social development is a cortical function that develops earlier than motor skills. Lack of social smile by four weeks is of concern. At birth, the infant is equipped with primitive reflexes. Certain primitive reflexes help in the normal physiology of infants. Sucking and rooting reflex helps inefficient feeding. Most of the primitive reflex disappears to facilitate the mature development process. For example, the grasp reflex disappears by six months, and the child develops mature grasp development from 6-12 months.
• Early and late childhood: Between ages 1 and 3 years, locomotion and language are crucial. The best predictor of cognitive function is language. Fine motor skills are related to self-help skills. The most common development in early childhood is to establish self-identity. A child may have independent existence by three years of age. The kids learn independent existence skills like feeding behavior, toilet training, and self dressing during this stage of early and late childhood. Questioning skills develop during early childhood development.   
• Adolescence:  Adolescence is hallmarked by puberty changes, which occur two years earlier in females than in males. Puberty changes are assessed using the Tanner staging. Acceptance of a new body and separation from home, and establishing oneself as an independent adult in society are the significant challenges in puberty.

Psychosocial Development 

Erikson has postulated eight stages of psychosocial development.

• Trust and mistrust in infancy (< 1 year):  Infants develop trust with a warm response from the caretaker.  
• Autonomy and doubt in the toddler age group ( one to three years):   Children feel autonomous if caregivers encourage independence. Otherwise, they will doubt their abilities.
• Initiative and guilt in the preschool age group (three to six years):  By imaginative play, kids experiment with their ambitions. If parents do not encourage their initiative, the kids will feel guilt.  
• Industry and inferiority in early school years:  In school, children learn to work as a group. They will have inferiority feelings if the peer environment is hostile.
• Identity and role confusion in adolescence:  Self-identity is a significant development during adolescence. 
• Intimacy and isolation in early adulthood:  Those who cannot establish relationships or intimacy are prone to be socially isolated.
• Generativity and stagnation in middle adulthood:  Parenting is the best example to guide the younger generation. 
• Ego integrity and despair in late adulthood:  People who are not satisfied with what they did during their lifetime will be in despair.
• Clinical Significance

Understanding normal growth and development milestones are important for a clinician evaluating pediatric patients. It isn't easy to recognize aberrance if you are not familiar with normal. By using growth charts and doing the developmental screening, oftentimes, challenges in care can be identified early.

Growth Charts

• The CDC charts include children raised in a variety of nutritional conditions in the United States. In the CDC charts, the normal range between 5th and 95th percentiles. 
• The WHO growth chart describes children from birth to five years raised under optimal environmental conditions. The normal range is expressed as a Z score between -2.0 and +2.0, corresponding to 2 and 98 percentiles. Z-scores are the number of Standard deviations from the mean.
• The WHO growth charts represent a growth standard, whereas the CDC growth chart represents a growth reference. WHO growth charts are used for children under two years of age, and the CDC growth charts are used in children for more than two years. 
• When using the WHO charts, the prevalence of short stature and obesity is similar to the CDC charts, but the underweight prevalence was lower than the CDC charts. [15] [16]
• Preterm infants 
• During the stay in the neonatal intensive care unit, preterm growth charts like Fenton growth charts are used for all preterm infants less than 37 weeks gestational age. Fenton charts can be used from 22 weeks gestational age and up to ten weeks post-term.
• WHO charts are useful to monitor the growth of preterm infants less than 37 weeks after discharge. The corrected postnatal age is used for up to two years. Corrected age for preterm kids is calculated as actual age in weeks - (40 weeks - gestational age at birth in weeks). [17]

Developmental Screening 

Only 20% of the children with developmental delay in the United States receive early intervention before three years. Early intervention is useful in high-risk children to improve their cognitive and academic performance. Less than 50 % of clinicians are only using standardized screening tools in practice. Time constraints, lack of training are essential barriers in using the developmental screening tool. The Ages and Stages Questionnaire (ASQ), the Parents' Evaluation of Developmental Status, and the Child Development Inventory are standard screening tools used in practice. ASQ tool can be used for up to 66 months. The PEDS tool can be used up to eight years of age.  Gross and fine motor milestones are assessed at every well-child visit in the first four years. Standardized developmental assessments using ASQ are mandatory at 9, 18, and 24 or 30 months. [18]  

The clinician may screen more frequently if there are risk factors like prematurity, lead exposure, or low birth weight. Autism screening needs to be done at 18 and 24 months of age. If the screening tool reveals developmental delay, the child needs referrals to developmental pediatricians. Children up to three years with developmental delay are referred to early intervention programs, and children above three years of age are referred to special education services. 

Red Flags in Growth and Development 

• Red flag signs in motor development are persistent fisting for more than three months, the persistence of primitive reflexes and rolling before two months, and hand dominance before 18 months. 
• No babbling by twelve months, no single words by sixteen months, no two-word sentences by two years, and loss of language skills are red flags.
• Children whose height or weight readings below the 5th percentile, above the 95th percentile, or cross two major centile lines need further evaluation.
• Enhancing Healthcare Team Outcomes

The health care team should understand the developmental stages that their patients go through during early childhood. We should increase the awareness of health care professionals about the importance of standardized growth monitoring and the appropriate use of growth charts. Also, they need adequate training for using standard developmental screening tools.

Every clinician and nurse managing pediatric patients should have appropriate awareness of referral service to early intervention for eligible patients. Interprofessional collaboration between clinicians, mid-level practitioners, and nurses can improve patient outcomes as developmental delays require prompt intervention when caught, and earlier is always better. Children up to three years with developmental delay are referred to early intervention programs, and children above three years of age are referred to special education services.

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Disclosure: Palanikumar Balasundaram declares no relevant financial relationships with ineligible companies.

Disclosure: Indirapriya Darshini Avulakunta declares no relevant financial relationships with ineligible companies.

This book is distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ), which permits others to distribute the work, provided that the article is not altered or used commercially. You are not required to obtain permission to distribute this article, provided that you credit the author and journal.

• Cite this Page Balasundaram P, Avulakunta ID. Human Growth and Development. [Updated 2023 Mar 8]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-.

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Human Growth and Development

Concepts of human growth and development.

Mary is dealing with two separate, though related, events in her life at the moment; bereavement and ageing. Both of these are transitions , and these always present us with a problem of adjustment. You might like to think about this in terms of your own life experience, as suggested in HGD: 17). Both of these changes in Mary’s life are beyond her control, and therefore likely to be harder to negotiate than those which she chose, like marrying Ken, or becoming a foster carer . But from what we know about Mary, she is likely to have qualities of resilience (HGD: 17); she has coped in the past with the challenges of fostering, and it is probable that she had secure attachments in her family of origin (Coleman, 2011, cited in HGD: 130). (Although, as we point out above, a strong attachment is not always a secure one (HGD: 61), it seems likely to have been so in Mary’s case).

As we noted in our discussion of family systems theory , (HGD: 187), different family members may be going through different stages of the family life cycle at the same time, and  Tracey, Mary’s foster-daughter,  is also going through her own process of transition at the moment. In our discussion of Tracey we noted the importance of emotion-focused strategies for building resilience to cope with life’s difficulties; they help us to manage our feelings about them, even when the difficulties themselves are beyond our control (HGD: 129). The other broad group of coping strategies is problem-focused , and these work better when we have some control over the situation (Lazarus and Folkman, 1984; Lazarus, 1993, cited in HGD: 129) Here Richard is picking up this distinction when he realises that he needs to take a different role with Mary than he did in similar situations in his previous human resources experience; he needs to just be with her rather than take problem-solving action. Working with emotion-focused strategies, however, does make different and emotionally more complex demands on those in a helping role, and this is what Richard is finding hard.

In addition, Ken’s death and Mary’s own ageing are just a part, albeit a major one, of a broader pattern of change and loss in her life. If Richard can give her the opportunity to acknowledge these other losses too, this will help her not to feel so overwhelmed by Ken’s death, which at the moment is carrying more than its own weight, and to make the transition into late adulthood. Erikson (HGD: 41) described the task of this last of his stages of psychosocial development as achieving integrity and avoiding despair. To achieve this ego integration (HGD: 218) one needs to be able to look back over one’s life and what one has achieved with a sense of acceptance and not too many regrets. We can see here that, although Mary has achieved much in her life, she has a tendency to undervalue this, giving all the credit to Ken, and she does have some regrets about educational and career opportunities not taken. If Richard can help her to re-evaluate her own achievements, this will help her towards ego integration.

Mary is feeling very disabled by her physical problems, and her confidence has been undermined by the fall that she had in the early days after Ken’s death. This has led her to avoid going out, and to withdraw socially. As a result she has become depressed, which has then further reinforced her withdrawal. It is often assumed that poor health and physical disability are an inevitable part of old age (HGD: 216), and according to the disengagement theory of ageing (Cummings and Henry 1961, cited in HGD: 221) Mary’s withdrawal from the world might be seen as age-appropriate. But the picture is more complex than this, as Mary’s GP has clearly realised. Anxiety and post-traumatic stress reactions are typical of early stages of bereavement (Murray Parkes and Prigerson, 2010, cited HGD: 236) and Mary’s reaction to her fall has probably been coloured by this. At a metaphorical level, she had lost her main emotional support, Ken, so she doubted her ability to stand without physical support in those early days, and this loss of confidence has stayed with her. And although the physical symptom which caused the fall, low blood pressure, has long since been stabilised, the inactivity and weight gain resulting from her withdrawal are now limiting her mobility.

The social context is important here too. In terms of the physical structure of her community, changes during Mary’s lifetime have made it harder for her to be independent and connected with her neighbours; most shops are now a bus ride away, and local social focuses, like pubs and cinema, have disappeared. So Mary is disabled both by her physical impairment and the additional barriers that these social changes have put in her way. Disability involves an interaction between the individual and society (HGD:  156), and needs to be understood in terms of social construction (HGD: 197) as well as bodily functioning. Other aspects of social construction are likely to be affecting Mary too; when she says she is reluctant to use a stick because it makes her feel like an old woman she is probably talking about her awareness of how others will see her, and how this will then affect the way she feels about herself. The negative stereotypes (HGD: 200) associated with old age are often summed up in the term ageism (HGD: 223). If she accepts the inevitability of her withdrawal from active engagement with the world, rather than feeling that she has a choice, Mary will be influenced by the kind of ageist stereotypes that the theory of disengagement mentioned above can sometimes be used to reinforce. There is evidence in her meeting with Richard of a woman who still has an appetite for social interaction and the potential to re-engage with the world as she works through the process of grieving for her husband. Social construction affects the grieving process too. When Mary says she should be getting over Ken’s death by now, she is responding to contemporary social norms about death and grieving, which, as we point out (HGD: 231) tend towards denial , with mourning practices and rituals not giving the kind of permission to express grief which they have done in other times and in other cultures. Those around her may be finding her grief hard to bear because it reminds them of their own mortality and vulnerability to loss, and so may be needing to hurry the process along.

We have seen the extent to which Mary’s sense of her identity has been bound up with her relationship with Ken. She is now grieving not only for Ken but for that part of herself which was invested in their relationship, and which she now feels she has lost. Hopefully, her work with Richard will help her to construct a new narrative (HGD: 237) for herself which does not end with Ken’s death, but helps her to let go of what she has lost while finding a new identity which does not depend on being one half of a couple. In terms of Stroebe and Schut’s dual process model of bereavement (HGD: 238–9), she needs some support in achieving more of a balance between a loss-orientated and restoration-orientated focus in coming to terms with Ken’s death. Richard may be able to help her reframe her regrets for lost learning opportunities as a desire to learn from new experiences in the present and future; the way she spoke about her learning from her role as a foster carer showed a spark of enthusiasm which contrasted with the sad focus on loss of most of her conversation with Richard.

It is never too late to revisit the developmental tasks of life’s stages. In working through her grief for Ken, Mary now has an opportunity to return to the unfinished business of her adolescence and develop a stronger, more independent sense of her own identity as a result.

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12.1: Case Study: How Our Bodies Change Throughout Life

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• Page ID 92759

• Tara Jo Holmberg
• Northwestern Connecticut Community College

Case Study: Lead Danger

Instead of using a phone to make a call, the infant in Figure \(\PageIndex{1}\) is using it for a purpose more suited to their current stage of life—to relieve the pain of teething. Although this may look cute, the tendency that infants and young children have of putting objects in their mouths makes them particularly vulnerable to being exposed to toxic substances in their environment that can seriously—and sometimes permanently—damage their health.

One such toxic substance is lead. Lead is a metal that can be found throughout the environment—including inside homes—and is toxic to humans. According to the Centers for Disease Control and Prevention (CDC), there are about a half million children in the U.S. between the ages of one and five who have blood lead levels above 5 micrograms per deciliter (µg/dL), the level at which steps should be taken to reduce lead exposure. There is no known safe blood level of lead in children.

This is why Paul, the father of a toddler named Lucas, brings Lucas to his pediatrician, Dr. Morrison, to test his blood for lead. Eighteen-month-old Lucas seems to be healthy, but the detrimental effects of lead exposure are often not apparent until later in life, so many medical professionals routinely screen children for lead toxicity between the ages of one and two.

Paul and his wife Vanessa are shocked to find out that Lucas’ blood lead level is 10 µg/dL, which is considered high. Medical treatment for lead poisoning is not recommended in children who do not have symptoms unless their blood level is at or over 45 µg/dL. However, Dr. Morrison tells Paul and Vanessa that they must take action to limit any further exposure, such as finding and eliminating the source of lead and limiting Lucas’ contact with potential lead-containing substances. Sources of lead that children may be exposed to include deteriorating lead-based paint, dust from peeling and cracking paint, water from lead pipes, toys, and jewelry, among others. Figure \(\PageIndex{2}\) illustrates some possible sources and routes of lead exposure in the home. One reason that young children are particularly susceptible to lead exposure is that they tend to put objects and unwashed hands into their mouths, which can directly introduce lead objects or lead-containing dust into their bodies.

Lead exposure in infants and young children can cause a variety of adverse health effects, some of which may not be noticeable until later in childhood. These effects include developmental delays, lower IQ, hyperactivity, behavior and learning problems, slowed growth, hearing problems, and anemia. When there is a very high level of exposure, serious immediate consequences of lead poisoning can occur, such as seizures, coma, and even death.

Paul and Vanessa are very concerned, not only for Lucas but also because Vanessa is three months pregnant. They are worried about whether Vanessa was also exposed to lead. If so, what effects could it have on the developing baby? Dr. Morrison shares their concern and strongly recommends that Vanessa get her blood tested for lead. Paul wonders if he should get tested, as well. Dr. Morrison says that testing Paul is less urgent than testing Vanessa, especially since Lucas’ lead level is not extremely high and Paul is not having any symptoms of lead poisoning—but if there is a source of lead in the home, it would be good for him to be tested eventually.

Lead clearly can cause significant adverse health effects, but its impact varies depending on the stage of life of the person exposed. Although lead exposure can cause health problems in adults, exposure to low levels of lead usually has much more of an impact on humans in earlier developmental stages, such as the embryo, fetus, infants, and young children. As you read this chapter, you will learn about these early stages, as well as the later stages of adolescence, early and middle adulthood, and old age. Many changes occur across a human’s lifespan, including physical characteristics, motor and cognitive abilities, behavior, and susceptibility to damage and disease.

At the end of this chapter, you will learn how Lucas likely became exposed to lead, whether his parents and developing sibling have been exposed, the potential impact on the family members at their different life stages, and what they—and you—can do to protect against the dangerous effects of lead exposure.

Chapter Overview: Human Growth and Development

In this chapter, you will learn about the growth and development of humans from fertilization to old age. Specifically, you will learn about:

• The germinal stage of human development, which starts at fertilization; goes through the early cell divisions and developmental stages of the zygote, morula, and blastocyst; and ends when the blastocyst implants in the uterus to become an embryo
• The embryonic stage, which starts at implantation and lasts until the eighth week after fertilization. This period involves significant growth and changes in the developing embryo, which occur through processes such as gastrulation, neurulation, and organogenesis.
• The three germ layers (which ultimately develop into different tissues of the body), and the extraembryonic tissues which nourish and protect the developing embryo and fetus, including the yolk sac, amnion, and placenta
• The fetal stage, which starts at the ninth week after fertilization and lasts until birth. This stage includes the final stages of prenatal growth and development, including the functioning of most organs and sensory systems.
• The differences between fetal and postnatal blood circulation and hemoglobin, due to the lungs not being used until birth
• Factors that affect fetal growth, birth weight, and viability
• Characteristics of newborns, and how health is assessed at birth
• Infancy, which is the first year of life—and the physical, motor, sensory, and cognitive changes that occur during this time period
• Childhood, which is defined biologically as the period between birth and adolescence—and the physical, cognitive, behavioral, and social changes that occur at different sub-stages of childhood
• Adolescence, which is the period between childhood and adulthood. This stage includes puberty—the period when sexual and physical maturation occurs—as well as further maturation of the brain, a stronger sense of personal identity, and changes in relationships.
• The stages of adulthood—early, middle, and old age—and the physical, cognitive, and social changes that typically occur during these times
• Susceptibility to diseases and common causes of death at different stages of adulthood, along with possible causes of aging

As you read the chapter, think about the following questions:

• Vanessa is three months pregnant. What are the major developmental events that have occurred in her pregnancy so far? If she has been exposed to lead, what effects might it have on her developing offspring?
• Lead exposure in infants and toddlers can cause developmental delays and other effects that may only become obvious later in childhood. What do you think is meant by a developmental delay? Why do you think that some of the effects of lead are only noticeable at older ages?
• Why is Dr. Morrison less concerned about Paul’s lead level than he is about Vanessa’s and Lucas’ levels?