The Human Immune System

What is the immune system? The body’s system that fight off infection and pathogens. The body relies on several lines of defense to keep pathogens out; however, when they do enter the body, warrior cells of the immune system travel to the site of infection to stop it.

PATHOGENS Specific microorganisms that cause disease. Bacteria Viruses Fungi Protozoa Parasites Pathogens can enter the body by direct/indirect contact and the air. Direct contact requires an infected person or animal to physically touch a healthy person. Indirect contact is when a pathogen can survive on nonliving surfaces. Coughing or sneezing releases droplets into the air which people then inhale.

Your Body’s Defense The skin is the first line of defense. It is a physical barrier that keeps pathogens from entering the body. The skin also secretes oil and sweat that makes the skin hypertonic and acidic. Mucous membranes (eyes, nose, ears, mouth) use hair-like cilia with sticky liquid to trap pathogens before they enter the body. “Warrier cells” travel through the body to reach the site of infection and attack it.

Your Body’s Defense The immune system has many types of white blood cells and proteins to fight pathogens. White blood cells find and kill pathogens. Basophils and mast cells release chemical signal when a pathogen enters the body. This attracts other white blood cells to the site of infection. If the pathogen is a parasite, eosinophils spray the parasite with poison. If the pathogen is a virus, bacterium, or fungus, phagocytes (nuetrophils and macrophages) go to work. Phagocytes are cells that destroy pathogens by surrounding and engulfing them.

Your Body’s Defense Following the phagocytes, lymphocytes reach the infection. T cells destroy body cells that is infected with pathogens. B cells produce proteins that inactivate pathogens that have not yet infected a body cell. Proteins help fight off invading pathogens: complement proteins, antibodies, and interferons. Antibodies are produced by B cells that destroy pathogens. Interpherons are produced by body cells that are infected by a virus. They stimulate uninfected body cells to produce enzymes that will prevent viruses from entering and infecting them. They also stimulate inflammation.

Types of Immunity Passive Immunity occurs without the body undergoing an immune response. Passed down from generations, through DNA, and mother-to-child. Active Immunity is when your body produces a response to a specific pathogen that has infected or is infecting the body. Acquired immunity is a type of active immunity that occurs after your immune system reacts to a pathogen invasion. This keeps you from becoming sick by a particular pathogen more than once.

Immune Responses Nonspecific Immunity Response Responses that happen in the same way to every pathogen. Skin as a physical barrier. Inflammatory Response – swelling, reddness, pain, itching, and increased warmth. Interferons – proteins that interfere with the production of new viruses. They buy time. Fever – chemicals are released that increase body temperature. This may slow down or stop the growth of some pathogens. Also speeds up several parts of the immune response.

Immune Responses Specific Immunity Responses Its purpose is to distinguish between “self” and “nonself” and they inactivate or kill any foreign substance or cell that enters the body. This leads to acquired immunity. Antigens are protein markers on the surface of cells and viruses that help to identify a foreign cell or virus. Two types of specific immune responses are triggered when a pathogen is detected: cellular and humoral response.

Immune Responses Cellular Immunity depends of T cells. T cells attach to infected body cells and cause them to burst. Humoral Immunity depends on antibodies. Antibodies fight pathogens by either causing them to burst, inactivating them, or causing them to clump.

Treatments Antibiotics are powerful medicines that fight bacterial infections. They either kill bacteria or keep them from reproducing. Vaccines are substances that contain the antigen of a pathogen. The antigen causes your immune system to produce memory cells, but you will not get sick because the pathogen is weakened and cannot reproduce or attack your cells.