The Immune System
The immune system (from the Latin word immunis, meaning: "free" or "untouched") is the body’s defense system. It is made up of a network of cells, tissues and organs that all work together to protect us against pathogens (disease-causing microorganisms, such as viruses, bacteria, parasites and fungi). Pathogens cause infection when they enter the body and begin to multiply. Disease occurs when your body’s cells are damaged because of the infection. Then signs and symptoms of illness appear.
Cells, organs and tissues of the immune system
The cells, organs and tissues of the immune system are located throughout the body, allowing for a quick response to infection. Study the image below from the Vaccine Makers Project to learn what organs and tissues are part of the immune system and where they are located.
White blood cells (also called leukocytes) are the cells of the immune system. They are responsible for protecting the body against pathogens. They are produced in the bone marrow and stored in several locations throughout the body, including the thymus, spleen and lymph nodes. They travel throughout the body via the bloodstream and in specialized vessels called lymphatic vessels.
There are several types of white blood cells, all with specific functions. Examples include phagocytes (like macrophages) that roam the body looking for any foreign invaders to destroy and lymphocytes (B cells and T cells) that are set into action in response to a specific pathogen such as a virus or bacterium. When a pathogen is detected the different types of white blood cells work together to recognize it and respond, protecting the body from disease.
The immune system has two main parts
The immune system has two main parts, the innate immune system and the adaptive immune system. You will learn more about these different systems and the roles that the cells of the immune system play in each, in the next two lessons.