23.1: Case Study: How Our Bodies Change Throughout Life

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.

Figure \(\PageIndex{1}\): Baby with a phone in its mouth

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.

Figure \(\PageIndex{2}\): Lead can be found in paint, water pipes, toys, jewelry, imported candies, jobs, and hobbies, etc.

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:

1. 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?
2. 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?
3. Why is Dr. Morrison less concerned about Paul’s lead level than he is about Vanessa’s and Lucas’ levels?

Attributions

1. Yummies by cplbasilisk, licensed CC BY 2.0 via Flickr
2. Lead Infographic by Center for Disease Control, public domain
3. Text adapted from Human Biology by CK-12 licensed CC BY-NC 3.0