1. By: Diego Mora Eugenio Martin-Carreras

2. The immune system is a system of biological structures and processes within an organism that protects against disease. For the immune system to be able to work it must be able to detect diseases, viruses, infections, etc., and distinguish them from healthy tissue.  The immune system is an organ system.

4.  In order to cause a disease, a pathogen must invade the body.  The first defense against disease is your skin.  Your skin is your largest organ. It helps keep pathogens out of your body.  Other barriers include mucus, sweat, and tears.

5.  Sweat is basically liquid waste.  The sweat contains salts, acids, and enzymes.  The acids and enzymes kill pathogens on your skin.  Tears also protect you from pathogens by washing them off of your eyes.  Tears also contain enzymes that help destroy some pathogens.

7.  The second line of defense is known as the inflammatory response. This is the body’s response to tissue damage.  White blood cells are specialized for fighting disease.  Several different types of white blood cells, plasma, and platelets are components of your immune system.

8.  The inflammatory response begins as soon as a pathogen enters the body.  If you get a cut, blood vessels near the cut expand allowing more blood to flow to the area. Then, plasma, the liquid part of your blood, fills the spaces between cells. This plasma carries white blood cells called macrophages to the injured area.  Macrophages are large white blood cells that engulf and destroy pathogens.

9.  Pathogens that enter the body can cause infections.  An infection is the multiplication of a pathogen in body tissue.  The most effective defense can be a fever.  A fever makes your body less suitable for the growth of harmful bacteria.  A fever also helps macrophages work more efficiently.

11.  The final line of defense is the immune response.  The immune response attacks specific pathogens using specialized cells and proteins.  Cells involved in the immune response are macrophages and other specialized white blood cells called T cells and B cells.  T cells are white blood cells that attack and kill harmful cells.  B cells are white blood cells that make antibodies.  An antibody is a Y-shaped protein that attaches to a specific foreign substance, know as an antigen.

12.  Each antibody is made to fit together precisely with a specific antigen. Antibodies cause the antigens to clump together and become harmless.  The clumped antigens are then engulfed by macrophages or destroyed by T cells.

13.  Some people are naturally immune to some diseases and some aren’t.  Active immunity is when you are exposed to a pathogen and your body naturally makes antibodies.  Passive immunity is when you obtain antibodies from another person who has the antibodies. It’s not natural.