Our body's defense system is a complex network of organs containing cells that recognize infections and diseases in the body and destroy them. When functioning properly, the immune system can distinguish between healthy tissue and critical viruses and bacteria. This system contains the thymus, white blood cells, antibodies, epidermis, cilia, mucus and saliva. The thymus is a small organ where white blood cells mature. White blood cells are divided into two groups. One creates antibodies that attack bacteria and the other helps destroy infected or cancerous cells. An example of how our cells and tissues work together is when layers of skin, such as the epidermis, protect our bodies from disease-causing viruses. Finally, eyelashes, mucus and saliva trap dust and other bacteria that may enter the nasal passages or mouth. To eliminate bacteria, they sneeze or cough. Together, all of these parts of the immune system work together to create immune responses. There are three types of lines of defense. Lines of defense are the abilities to defend and protect the body against...