GED Science Practice Test: Human Disease

Errors in metabolism or homeostasis may indicate the presence of disease. For instance, heart failure in humans may occur when negative feedback mechanisms become overwhelmed and destructive positive feedback mechanisms take over. Many human diseases can result from a homeostatic imbalance, including diabetes, dehydration, hypoglycemia, hyperglycemia, gout and any disease caused by the presence of a toxin in the bloodstream. In mild cases, the body may be able to get back to homeostatic balance independently, but in more severe cases, medical intervention (e.g. drugs, medical treatments or procedures) may be needed to regain homeostasis and prevent permanent damage.

A disease is an abnormal condition that affects the structure or function of an organism, and usually disrupts homeostasis or metabolism in some way. Most diseases are associated with – and identified by – specific symptoms and signs. Diseases can be classified in many ways.  One way is to classify the disease by body system, such as cardiovascular disease (a disease of the heart and vessels), or endocrine disease (a disease of the endocrine system).  Another way to classify disease is by their cause:

  • Pathogenic diseases, or infection diseases are caused by an external sources, such as bacteria or viruses. Examples include the common cold, botulism, and AIDS.
  • Deficiency diseases are caused by a deficiency of a nutrient, sunlight, hormone, or other resource needed for normal health and functioning. Examples include rickets and anemia.
  • Hereditary diseases are caused by inheriting a gene that confers a disorder. Examples include sickle cell anemia, Tay-Sachs disease, and some cancers.
  • Physiological diseases are caused by internal abnormalities in the function of a cell, tissue, organ, or organ system. Examples include heart disease, rheumatoid arthritis, allergies, and some cancers.

Inflammation: A particularly interesting aspect of disease is inflammation.   Inflammation is a complex process involving immune cells, blood vessels, and other chemicals.  You experience inflammation as heat, redness, pain, and swelling.  If you cut your finger, and it becomes infected, that cut and your finger will become inflamed.  If it becomes particularly infected, it might ooze pus, which are dead white blood cells that came to fight the infection.

Inflammation is a welcome process in such circumstances.  Too little inflammation, and a bacterial infection could escalate .  However, chronic inflammation is implicated in a number of diseases, such as hay fever, gum disease, rheumatoid arthritis, and others.  Rheumatoid arthritis is an auto-immune disease, which means that the body mistakenly attacks itself.  In this disease, the body attacks the soft lining of the joints.  This causes a chronic inflammation of the joints which can further damage the cartilage and bone around the joint.


Inflammation also plays a large role in the risk of getting cancer of the esophagus, the tube that connects the mouth with the stomach.  People who have chronic acid reflux have large amounts of acid irritate the part of the esophagus close to the stomach.  This irritation causes inflammation, which increases the risk of DNA damage.  This irritation can create changes in the structure of the esophagus, called Barrett’s esophagus.


Chronic inflammation is an example of a positive feedback system.  The more inflammation there is, the more inflammatory chemicals are called to the site, which in turn causes more inflammation.  In many diseases that exhibit and/or are caused by chronic inflammation, one form of treatment is to reduce inflammation by reducing swelling.  Steroids are a type of drug that lowers swelling.

Approaches to Dealing with Disease: There are two main approaches to deal with disease:  prevention and treatment.  Prevention tries to anticipate and prevent the disease from occurring.  For example, you can prevent heart disease by lowering the amount of fats and cholesterol in your diet. You can also prevent heart disease by using medications such as cholesterol-lowering drugs. Treatment tries to alleviate the symptoms of disease, or in some cases, cure the disease altogether.  For example, antibiotics can be given to treat, and hopefully cure, a bacterial infection.  There are three main methods to prevent or treat disease:  nutrition, drugs, surgery, and genetic counseling.

Nutrition is about providing the body with the nutrients and food that are needed for human growth. Nutrients are the components in foods that an organism utilizes to survive and grow, and they play an important role in maintaining homeostasis and health and helping to prevent certain kinds of disease. In some cases, improving nutrition can help treat or cure disease. Macronutrients, such as carbohydrates, lipids, and proteins, provide the bulk energy for an organism’s metabolic system to function, while micronutrients, which include vitamins and minerals, provide the necessary cofactors for metabolism to be carried out. When a nutritional deficiency occurs for a prolonged period of time, a deficiency disease will likely result.

Drugs are chemical substances that are used in the treatment or prevention of disease. Many drugs are used to treat diseases or to counteract or lessen their symptoms, and can be used for both short-term conditions (e.g., antibiotic drugs for infections) or for chronic conditions (e.g., steroid drugs to help treat the symptoms of severe dust allergies). Additionally, some drugs can be used for psychological effects – for example, one of the most commonly used drugs is caffeine, which many people use to feel more alert and active. However, there are also recreational drugs that can have negative effects, including addiction. Furthermore, some drugs that are meant to support physical well-being (e.g. certain painkillers) can have become addictive and have a negative effect on human health if abused or taken incorrectly.

Surgery is an effective treatment for diseases which require removal of abnormal tissues or organs (such as a diseased gallbladder), or unwelcome growths on those tissues or organs (such as cancer).  Again, in some cases, treatment through surgery can cure the disease.  Surgery is an extreme option for  most diseases, and other, less invasive methods are preferred first.

Genetic counseling is an approach to disease that seeks to inform people about any genetic abnormalities they or their offspring may have.  Genetic counselors help people understand the risks associated with diseases they may have genes for.  For example, Huntington’s disease is a disease that causes a breakdown of the nerve cells in the brain.  Because it is a disease caused by a dominant gene, offspring only have to get one copy of the gene from either their mother or their father to get the disease.  Genetic testing, and subsequent counseling, may lead a couple with either partner carrying the gene to opt not to have their own children.  The following Punnett Square shows the risk of having a child with Huntington’s disease if one parent is affected:


Additionally, genetic testing and counseling can identify people who care a gene that predisposes them to breast cancer.  In these cases, the person may opt for more regular testing for breast cancer.


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