In today's modern world, we are products of a highly technological era, surrounded by machines designed to serve every imaginable purpose. The list of mechanical wonders is endless: dishwashers, refrigerators, telephones, computers, automobiles - all have become commonplace in our everyday lives. In fact, it's difficult to imagine going without these modern conveniences. Unfortunately, when a machine breaks down, it does not have the capacity to repair itself, no matter how advance or well-designed it may be. We must either replace the item, or seek out the help of someone with specialized knowledge to fix the faulty machine. But one machine does exist that comes with its own built-in and highly specialized repair mechanism: The Human Body.

Through an organic rather than technological wonder, the human body is nevertheless an intricate and sophisticated machine, made all the more remarkable because every human is different and unique. When the body "breaks down", falling victim to illness and disease, it is not possible to simply go out and replace it with a new one. Luckily, the body comes equipped with its own mechanism of defense and repair in the form of an elaborate immune system.

The immune system is a complex network of cells and organs, not confined to any one area of the body. It is programmed to fight off any foreign substance that threatens the health of the body. In addition, the immune system clears away dead cells and destroys mutant or altered cells that could become cancerous. It is only within the past 30 years that scientists have really begun to gain even a rudimentary understanding of this valuable and intricate system.

Two main components of the immune system include the bone marrow (which produces white blood cells or leukocytes, that circulate throughout the body to detect and destroy harmful substances) and the thymus (a small organ located above the heart that serves as a sort of training center for immune cells). Specialized cells of the immune system include B cells (which produce antibodies against infectious agents), T cells (which are specially trained by the thymus to recognize the specific invaders), natural killer cells (which wonder through the body and attack cancerous cells) and phagocytes such as the monocyte and macrophage ; also known as "eating cells" (which engulf and destroy microorganisms and debris). Together, these various cells create a strong defense against any substance that threatens the health of the body.

In 1979, immunologist Edwin Blalock discovered that immune cells manufacture several hormones which enable the immune system to coordinate its activities with the bodys' other systems. All of these systems work in tandem to keep us healthy and protect us from threat of foreign substances. The human body is a marvelous but irreplaceable machine and the task of the immune system is to provide the body with superior protection, helping this machine to last a long, long time.

The Human Body consist of:

* Respiratory System
* Circulatory System
* Digestive System
* Nervous System
* Musculoskeletal System
* Integumentary System
* Human Eye
* Endocrine System
* Reproductive System