Causes of Noninfectious Diseases
Most noninfectious diseases have more than one cause. The causes may include genes and an
unhealthy lifestyle. Genes may increase the chances that people will have certain diseases.
However, other factors may determine whether the diseases actually develop. For example,
what people eat or whether they smoke may also play a role.
Several noninfectious diseases are discussed in other chapters. For example, heart disease is
discussed in Cardiovascular System chapter. In this lesson, the focus is on cancer, diabetes,
and diseases of the immune system.
Cancer
Canceris a disease in which abnormal cells divide out of control. Normally, the body has
safeguards that prevent abnormal cells from dividing. In cancer, these safeguards fail.
What Causes Cancer?
Cancer is usually caused by mutations. From theCell Division, Reproduction, and DNA
chapter, you know that mutations are random errors in genes. Mutations that lead to cancer
(usuallymultiplemutationsinthesamecell)usuallyoccuringenesthatcontrolthecellcycle.
Due to the mutations, abnormal cells divide uncontrollably. This often leads to a tumor. A
tumoris a mass of abnormal tissue. As a tumor grows, it may harm normal tissues around
it.
Anything that can cause cancer is called acarcinogen. Carcinogens may be pathogens,
chemicals, or radiation. Figure 1 gives examples of carcinogens of each type.
Causes of Cancer
Pathogens Pathogens that cause cancer include the human papilloma virus (HPV) and
the hepatitis B virus. HPV is spread through sexual contact. It can cause cancer of
the reproductive system in females. The hepatitis B virus is spread through sexual
contact or contact with blood containing the virus. It can cause cancer of the liver
(Figures21.9and21.10).
Chemicals Many different chemical substances cause cancer. Dozens of chemicals in to-
bacco smoke, including nicotine, have been shown to cause cancer. In fact, tobacco
smoke is one of the main sources of chemical carcinogens. Smoking tobacco increases
the risk of cancer of the lung, mouth, throat, and bladder. Using smokeless tobacco
can also cause cancer.