Chapter 17 Review

chapter 17Review

Key Terms

Learning Objectives Revisited

• Identify the different types of human diseases.

  Human diseases can be categorized as either infectious or noninfectious. Infectious diseases are caused by pathogens such as viruses, bacteria, fungi, protists, and helminths. Human diseases can also be categorized as either acute, which means they rapidly impair a body’s functions, or chronic, which means they slowly impair a body’s functions.

• Understand the risk factors for human chronic diseases.

  Risk factors for human health differ between low- and high-income countries. In low-income countries, the top risk factors include unsafe drinking water, poor sanitation, and malnutrition. In high-income countries, the top risk factors include tobacco use, less active lifestyles, poor nutrition, and overeating that leads to high blood pressure and obesity.

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• Discuss the historically important human diseases.

  Among the historically important infectious diseases, plague is caused by a bacterium that is carried by fleas, malaria is caused by several different species of protists, and tuberculosis is caused by a bacterium that primarily infects the lungs.

• Identify the major emergent infectious diseases.

  Among the emerging infectious diseases, HIV/AIDS is caused by a virus that weakens the immune system, Ebola hemorrhagic fever is caused by a highly lethal virus, and mad cow disease is caused by a prion that damages the nervous system. In addition, the viruses that cause bird flu and swine flu are easily spread and sometimes lethal, SARS is a type of pneumonia caused by a virus, and West Nile virus normally infects birds but can be transmitted to humans by mosquitoes.

• Discuss the future challenges for improving human health

  The future challenges for improving human health including the improvement of nutrition and sanitation in low-income regions of the world and promoting healthier lifestyles in high-income regions of the world. We also need to educate people about the importance of taking the full duration of medicines that combat pathogens to prevent the evolution of drug-resistant strains of pathogens. Finally, we need to continue to develop rapid response to emerging infectious diseases to reduce the probability of them spreading worldwide.

• Identify the major types of harmful chemicals.

  The major types of harmful chemicals are neurotoxins, carcinogens, teratogens, allergens, and endocrine disruptors. Neurotoxins disrupt the nervous systems of animals and they include insecticides, lead, and mercury. Carcinogens are cancer-causing chemicals that include asbestos, formaldehyde, radon, and chemicals from tobacco. Teratogens interfere with the normal development of embryos or fetuses and include thalidomide and alcohol. Allergens cause abnormally strong immune responses and a given allergen typically only affects a small fraction of people. Endocrine disruptors such as hormones from animal rearing facilities interfere with the normal functioning of hormones in organisms.

• Explain how scientists determine the concentrations of chemicals that harm organisms.

  Scientists can conduct LD50 experiments to determine lethal effects of chemicals and ED50 experiments to determine sublethal effects of chemicals. They can also follow large groups of individuals backward in time using retrospective studies or forward in time using prospective studies. Once we know the chemical concentrations that can cause harm, we also need to determine the routes of exposure by which an individual may come in contact with the chemical as well as the chemical’s solubility and its potential to bioaccumulate and biomagnify.

• Explain the processes of qualitative versus quantitative risk assessment.

  For a given environmental hazard, we can qualitatively categorize risks as relatively low, medium, or high. However, the actual risk of a given hazard may be quite different from our qualitative assessments. Quantitative assessments use actual data to determine the actual probability of various risks, either based on government death statistics or by calculating the probability of being exposed to a hazard multiplied by the probability of being harmed if exposed.

• Understand how to determine the amount of risk that can be tolerated.

  Individuals differ in how much risk they are willing to tolerate. For most environmental hazards, we often set risk tolerance at 1 in 1 million.

• Discuss how risk management balances potential harm against other factors.

  Understanding the level of risk is important, but we must also assess the effects of trying to reduce the risk. Such effects include economic, political, and social considerations that collectively can come to some compromise that balances all of these factors. Whereas risk assessment is conducted by environmental scientists, risk management is typically conducted by local, national, or international government agencies.

• Contrast the innocent-until-proven-guilty principle and the precautionary principle.

  According to the innocent-until-proven-guilty principle, a potential hazard should not be considered harmful until it can definitively be demonstrated to cause harm. According to the precautionary principle, when a hazard is plausible but not yet certain, we should reduce or remove the hazard.