The Body’s Defense System Playing Defense The Body’s Defense System

External Defenses

A pathogen is an organism, a virus, or a protein that causes disease Your skin provides external protection against pathogens that may enter the body Hair, nails, and sweat and oil glands help provide protection Eyelashes and ear hair keep particles in the air from entering the body Mucus in your nose and mouth wash pathogens down into your stomach to be digested

Internal Defenses

Sometimes, skin is cut and pathogens can enter the body When this occurs, blood flow increases to the area causing swelling and redness – this is called inflammation The body temperature is raised – fever – this response slows the growth of the bacteria or other pathogen If these internal defenses don’t work, then the immune system responds

The Immune System

The immune system is made up of tissues and specialized white blood cells that recognize and attack foreign substances in the body White blood cells are able to move out of the blood vessels and patrol all the tissues of the body There are three types of white blood cells: macrophage, T cells, and B cells A macrophage is a white blood cell that destroys pathogens by engulfing and digesting them Macrophages help start the body’s immune response to antigens Antigens can be pathogens or any foreign material in the body

Some T cells coordinate the body’s immune response, while others attack infected cells Helper T cells activate other T cells, called killer T cells Killer T cells attack infected body cells Helper T cells also activate B cells B cells make antibodies that attach to specific antigens An antibody is a specialized protein that binds to a specific antigen to tag it for destruction

Building Immunity

The body builds immunity against a disease when it is exposed to the pathogen that causes the disease Immunity is the ability to resist or recover from an infectious disease Immunity is passed from a mother to fetus Can result from the body being infected Can result from the body being vaccinated Once your body has fought a pathogen, the body produces memory cells – these cells remember a certain pathogen Memory cell become activated when the pathogen enters the body Your body immediately starts to make many T cells and B cells to attack Memory cells make you immune to the pathogen

A vaccine is a substance prepared from killed or weakened pathogens that is introduced into the body to produce immunity The vaccine stimulates the body to make an immune response. B cells make antibodies to attack the specific pathogen being injected Vaccines are used to trigger the body to make memory cells for a certain pathogen without causing illness

Challenges to the Immune System

Allergies are an immune system’s reaction to foreign antigens that are not dangerous to most people Can be caused by foods, medicines or types of pollen or mold Cancer is a group of diseases in which cells divide at an uncontrolled rate – the immune system may not be able to stop the cancer cells Immune deficiency occurs when the immune system fails to develop or becomes weakened For example, the AIDS virus infects the helper T cells – when the number of helper T cells becomes low, neither the killer T cell nor the B cell immune response can be activated A disease in which the immune system attacks the body’s own cells is called an autoimmune disease For example, rheumatoid arthritis is a disease in which the immune system attacks the joints of the body