What Causes us to Feel Sick?
Allergies: Have you ever had a stuffy nose, sneezing, itchy, watering eyes and a tickly throat all rolled into one? Chances are that you are experiencing an allergic reaction. An allergy results when the immune system is overly sensitive to certain substances called allergens. Allergens can be anything like dust, pollen, feathers, animal hair or certain types of food. When an allergen enters the body, your body acts as though it needs to fight it off and produces antibodies that produce substances called histamines. Histamines are chemicals that are responsible for all of the icky symptoms listed above. Click here to find out more about allergies!	This is a magnified piece of pollen. This is considered to be an allergen. This is a picture of a dust mite! I don’t know about you, but I don’t want to breathe this critter in! No wonder dust is an allergen to many.
	Acquired Immune Deficiency Syndrome or AIDS or HIV, human immunodeficiency virus: AIDS is a disease that affects the immune system. It hides out in healthy body cells. It then attacks white blood cells and prevents them from doing their job, which is to protect your body from invading organisms. Even though the immune system produces antibodies to fight the disease, HIV escapes them by growing within the cells that make up the immune system. Because your body cannot defend itself against invaders, over time the body cannot keep up with the invaders, weakens and then the person eventually dies. You can contract HIV or AIDS only if you have direct contact with the blood or body secretions (such as tears, saliva or mucus) of an infected person. It can be spread through sexual contact or through infected needles. There is no cure for AIDS at this time. However, there are drugs that slow the spread of the virus in the body that can help infected people to live longer. Click to visit a website to learn more about AIDS.

Infectious Diseases Caused by Viruses and Bacteria:

Diseases that are transmitted among people by disease causing microorganisms are called infectious diseases.

They can be transmitted in three ways:

· By people- germs from colds, the flu, measles, mumps and tuberculosis are spread through coughing, sneezing or sick people not washing their hands after going to the bathroom. Colds are usually caused by viruses.

· By animals- ticks can give us Lyme disease and Rocky Mountain spotted fever and we can contract rabies from infected mammals, such as raccoons and birds.

· By non-living things- contaminated food or water can cause food poisoning. Poor sanitation can also cause the spread of diseases such as hepatitis, cholera and typhoid.

Noninfectious Diseases:

Diseases not caused by microorganisms are called noninfectious diseases. These noninfectious diseases can harm or irritate the body. They can be caused by not eating a balanced diet, from stress or worry or from when the immune system fails to function properly.

One Common Noninfectious Disease:

Cancer:

Cancer is a disease in which cells multiply uncontrollably, killing healthy tissue. These cells are not from outside of the body; they are from the body’s own cells. When the cells multiply at a rate that is more rapid than usual, they form a tumor, or mass of tissue. If the tumor is malignant, it will invade and destroy surrounding tissue.

Scientists are not completely sure about what causes cancer. Some possible causes of cancer might be prolonged contact with chemicals that make us sick or the tendency to get cancer may be passed from parents to their children through their genes.

The brain scan on the left shows brain cancer.

The dark areas on the scan on the right show where tumors have been removed.

Click here to visit websites to learn more about cancer and how to treat it:

This site describes the link between the immune system and cancer: http://www.cancerresearch.org/immresp.html

The American Cancer society: http://www.cancer.org/docroot/home/index.asp

The National Cancer Institute: http://www.nci.nih.gov/

How Can We Keep Our Immune Systems Working Properly to Maintain a Balance?

· Eat a balanced diet.

· Wash your hands often, especially before eating

· Exercise often.

Visit your doctor regularly for check ups.

How Does the Immune System Work with Other Systems in the Body to Maintain Good Health?

The immune system is closely related to the circulatory system and the skeletal system.

· Your skeletal system does more than keep you from being a blobby mass of flesh that cannot move. It also plays an important role in the production of white blood cells that are responsible for defending against invaders.
	· The circulatory system is important to the immune system because it transports white blood cells and the antibodies they produce to the site of an invader or infection. The white blood cells and antibodies travel through blood vessels called veins, arteries and capillaries along with the oxygen and nutrient delivering red blood cells.

Source used to create this web-page:

Human Biology and Health; Prentice Hall, 1994

http://www.niaid.nih.gov/final/immun/immun.htm information on the immune system