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21: Disease

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    This chapter discusses disease as homeostatic dysfunction and explores causes and types of human diseases, including both infectious diseases and noninfectious diseases. Special emphasis is given to sexually transmitted infections, HIV/AIDS, and cancer.

    • 21.1: Case Study: Threats to Our Health
      Nineteen-year-old Ximena spent a relaxing week of summer vacation visiting her grandparents in New Jersey. She particularly enjoyed taking their dog on long walks in the woods near their home, occasionally spotting deer on the overgrown paths. The discovery of a distinctive rash upon her return, however, leads to a very serious diagnosis.
    • 21.2: Homeostasis and Disease
      When the human body is maintained in a steady state, the condition is called homeostasis. The body consists of trillions of cells that perform many different functions, but all of them require a similar internal environment with important variables kept within narrow ranges. For example, cells require a certain range of body temperature, pH of extracellular fluids, and concentrations of mineral ions and glucose in the blood. Each of these variables must be maintained within a narrow range of val
    • 21.3: Infectious Diseases
      Her real name was Mary Mallon (1869-1938), but she was nicknamed "Typhoid Mary." She gained notoriety (as evidenced by this newspaper article) by being the first person in the United States to be identified as an asymptomatic carrier of the pathogen that causes typhoid fever.
    • 21.4: Sexually Transmitted Infections
      Syphilis is one of many sexually transmitted infections. A sexually transmitted infection (STI)is an infection caused by a pathogen that spreads mainly through sexual contact. This generally involves direct contact between mucous membranes or their secretions. To be considered an STI, an infection must have only a small chance of spreading naturally in other ways.
    • 21.5: HIV and AIDS
      AIDS stands for acquired immunodeficiency syndrome and is a disease caused by infection with the human immunodeficiency virus, or HIV. HIV is a sexually transmitted virus that infects and destroys helper T cells of the human immune system. AIDS eventually develops in most people with untreated HIV infections, usually several years after the initial infection with the virus. AIDS is diagnosed when the immune system has been weakened to the point that it can no longer fight off diseases.
    • 21.6: Noninfectious Diseases
      Noninfectious diseases include all diseases that are not caused by pathogens. Instead, noninfectious diseases are generally caused by genetic or environmental factors other than pathogens, such as toxic environmental exposures or unhealthy lifestyle choices. Most noninfectious diseases have a complex, multifactorial set of causes, often including a mix of genetic and environmental variables.
    • 21.7: Cancer
      Cancer is actually a group of more than 100 diseases, all of which involve abnormal cell growth with the potential to invade or spread to other parts of the body. In general terms, cancer occurs when the cell cycle is no longer regulated due to DNA damage. The number of potential underlying causes of this DNA damage is great, so there are many different risk factors for cancer. Any cells that become cancerous divide more quickly than normal cells. They may form a mass of abnormal cells called a
    • 21.8: Case Study Conclusion: Lyme and Chapter Summary
      As you learned in the beginning of the chapter, Ximena came down with symptoms of Lyme disease, including the distinctive bulls-eye rash that allowed for a relatively quick diagnosis and the beginning of treatment. Lyme disease is a common infectious disease transmitted by ticks—and the most common vector-borne disease in the U.S. Thankfully, there are steps you can take to protect yourself!

    Thumbnail: This colorized transmission electron microscopic (TEM) image revealed some of the ultrastructural morphology displayed by an Ebola virus virion. (Public Domain; Frederick A. Murphy via CDC).​​​​

    21: Disease is shared under a CK-12 license and was authored, remixed, and/or curated by Suzanne Wakim & Mandeep Grewal via source content that was edited to conform to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.

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    CK-12 Foundation is licensed under CK-12 Curriculum Materials License