The purpose of the immune system is to protect the body from infection.

Its function is to destroy foreign matter, invading pathogens(germs) and protein.

The immune system is made up of LYMPHOID TISSUE, fluid called LYMPH and WHITE BLOOD CELLS.

The immune system is closely associated with the blood circulatory system. The LYMPHATIC SYSTEM is often called the SECOND CIRCULATORY SYSTEM.

The cells of the immune system cluster in LYMPHOID TISSUE. The lymphoid tissues include the ADENOIDS and TONSILS, the THYMUS GLAND, BONE MARROW, the SPLEEN and the LYMPH NODES.

The human body’s defense system is all of the cells, organs and chemicals that protect the body against foreign invaders. Invaders like PATHOGENIC (capable of producing a disease) BACTERIA, FUNGI, VIRUSES and FOREIGN MATTER.

The body has 3 BASIC DEFENSE SYSTEMS against infection: NON-SPECIFIC DEFENSES, NON-SPECIFIC IMMUNE DEFENSES and SPECIFIC IMMUNE DEFENSES.
1. NON-SPECIFIC DEFENSES
– The body uses a variety of simple defenses to keep disease causing pathogens out. Because these defenses do not target a specific pathogen, they are called non-specific defenses.
– The human body’s first way to protect itself against the invasion of pathogens is to not allow them into the body.
– When the body is attacked by pathogens, it puts up a series of defenses designed to destroy the invader and maintain the body’s health.

SKIN
– The body’s first way to protect itself is to not let pathogenic invaders into the body. The SKIN is the organ responsible for this protection.
– Clean, unbroken skin is thick enough and tough enough to prevent most pathogenic invaders from penetration it.
– The skin not only provides a physical barrier to many foreign substances, but it also has chemicals on its surface that can destroy many of these pathogens.
– Pathogens that land on the skin usually don’t live long, because the skin has a germicidal quality that inhibits their growth.

OTHER DEFENSES
– Even with the skins protection, pathogens can make their way into the body, usually through the openings in the skin; the EYES, NOSE, EARS, REPRODUCTIVE ORGANS and MOUTH.
EYES
– Most pathogens that enter through the eyes do not live long; they are usually dissolved by LYSOZYME, an enzyme in tears. However some strong pathogens can survive and may cause eye infections, including CONJUNCTIVITIS(pink eye) or TRACOMA.
MOUTH
– Thousands of pathogens enter the mouth daily with our food and drink. Few, however survive to reach the intestines.
– The SALIVA in the mouth is able to kill many of the invaders. Those that do reach the stomach are usually killed by the HYDROCHLORIC ACID and PEPSIN. However, some do survive to cause illnesses, like TYPHOID or CHOLERA.
NASAL PASSAGES
– Large numbers of pathogens are BREATHE in through the NOSE from the surrounding air, however few reach the lungs.
– The NASAL PASSAGES act as a complicated filtering system, lined with hairs that trap many pathogens. In addition MUCOUS MEMBRANES that line the air passages secrete sticky mucous that traps pathogens.
– SNEEZING also expels pathogens out of the nasal passage.
– Pathogens that do not reach the breathing tubes become trapped in mucous secretions. In addition CILIA of the cells that line the air tubes sweep the mucous trapped pathogen back to the throat where they are swallowed and then destroyed by the hydrochloric acid and pepsin in the stomach.
– However, some pathogens do survive and cause illnesses like COLDS, PNEUMONIA, and INFLUENZA.

2. NON-SPECIFIC IMMUNE DEFENSES
– Once the pathogens are inside the body the other defense mechanism, the defenses of the immune system, began to work to fight the invading pathogens.
– Since theses immune defenses do not target specific pathogens, they are called non-specific immune defenses. The include PHAGOCYTES and INTERFERONS.
PHAGOCYTES
– Phagocytes are cells that engulf and consume invaders. They are the immune system’s first line of defense.
– Among the phagocytes are MACROPHAGES and NEUTROPHILS; two types of white blood cells that engulf(phagocytize) invading pathogens/microorganisms.
– Some macrophages stay in the spleen and lymph nodes, where they engulf any invader that passes their way.
– Other macrophages and neutrophils travel through the body searching for invaders.
– INFLAMMATION is one of the non-specific defenses. Redness, warmth and swelling occur at the area of an injury or infection. These symptoms mean that blood vessels have dilated to increase the blood flow to the affected area. Chemicals releases from the damaged platelets attract the traveling macrophages and neutrophils. These cells gather at the site of the infection and ingest the foreign pathogen/bacteria. The phagocytes ingest large numbers of bacteria and are themselves killed by the BACTERIAL TOXINS (poisons). The accumulated dead bodies of macrophages and neutrophils form PUS.
INTERFERONS
– Interferon is protein secreted by infected cells that limit the harmful effects of viruses.

3. SPECIFIC IMMUNE DEFENSES
– Specific immune defenses are specialized responses that target specific invading pathogens.
– The circulatory, lymphatic and other systems coordinate to target specific pathogens.
– The cells of the immune system are able to recognize and act upon invading microorganisms that enter the body.
– Any foreign substance or microorganism that causes the immune system to react is called an ANTIGEN.
– Antigens are usually proteins, glycoproteins (carbohydrates-protein molecules), or carbohydrates, that are carried on the cell membranes of invading microorganisms.
– Both T-CELLS and B-CELLS have the ability to tell the difference between your cells and those that don’t belong to you. All cells contain antigens, molecules that allow the lymphocytes to tell the difference. Cells that are yours contain SELF-ANTIGENS and foreign cells contain NON-SELF -ANTIGENS.

LYMPHOCYTES
– Lymphocytes are the immune systems second line of defense.
– Lymphocytes are found in high concentrations in the lymphatic system; when they are inactive they are stored in the white pulp of the liver.
– There are 2 types of lymphocytes; T-CELLS and B-CELLS. Working together these two cells carry out a very organized approach to killing invaders, know as the IMMUNE RESPONSE.
– T-CELLS mature in the thymus and are transported through out the body, where they facilitate CELL-MEDIATED IMMUNITY by targeting and neutralizing pathogens. (Cell-mediated immunity occurs when phagocytes engulf and partially digest a pathogen, and then the T-cells recognize and destroy the phagocyte and the pathogen).
– B-CELLS facilitate ANTIBODY-MEDIATED IMMUNITY by producing defensive proteins called ANTIBODIES, which circulate throughout the body to target and destroy pathogens.
– B-cells carry specific antigen-recognition proteins. Each cell is a specialist, carrying only one kind of recognition protein.
– When a newly produced B-cell meets with a matching antigen, the B-cell is activated and the antigen attaches to the recognition site on the membrane of the B-cell and immobilizes it, then the macrophages and neutrophils ingest it.

THE IMMUNE RESPONSE
– The immune response is triggered by the release of an ALARM CHEMICAL called INTERLEUKIN-1 by the macrophage white blood cells.
– This alarm chemical causes the response of a type of lymphocyte called the HELPER T-CELL. The helper T-cell does not actively kill pathogens in the body, but it stimulates two additional lymphocytes, KILLER T-CELLS and B-CELLS to respond.
– Killer T-cells travel through the blood and lymph fluid and attack and destroy pathogens.
– Killer T-cells are able to recognize foreign substances when the receptor proteins found on their cell membrane match the pathogen. The body produces killer T-cells with many different kinds of receptor proteins.
– The B-cells produce a substance called an ANTIBODY that circulates in the blood and lymph until it attached to a foreign substance, marking it for destruction by the T-cells.
– The B-cells also remember the pathogens that attack the body. These MEMORY B-CELLS will quickly initiate the cellular defense against the pathogen that has previously entered the body. This quick response to a pathogen entering the body a second time lessens the dangerous effects of the pathogen. This is called the ANAMNESTIC RESPONSE.

FEVER DEFENSE
– Having a fever, as long as it doesn’t get too high (103 degrees F or above) is helping your body regain its health.
– When pathogens are recognized by white blood cells, they alert the anterior hypothalamus in the brain, to increase the normal body temperature.
– Raising the body’s temperature helps fight against invading pathogens. Many pathogens grow slower in high temperatures; allowing the body more time to build up its defenses.
– Raising the body’s temperature increases the body’s metabolic rate. This increases the rate of white blood cell production and speeds up the repair of damaged tissue.
– When the temperature of an adult raises to 103 degrees F, damage to the body may begin to take place, medication should be used at this point to bring the fever down.

IMMUNIZATION
– Immunization is the ability to resist the attack of a particular disease-producing pathogen.
– Immunity to one type of pathogen does not give a person immunity to other types of pathogens.
– ACTIVE IMMUNITY happens when an antibody is produced by a person’s own body cells.
– Active immunity can happen in two ways; by getting the disease and recovering from it or by being immunized against the disease.
– Immunization that produce active immunity involves the injection of weakened disease pathogens that stimulate antibody production, but produce only mild symptoms or none at all.
– Active immunization is long-lasting because the body cells continue to produce the antibodies.
– An injection of GAMMA GLOBULINS can give a person temporary immunity against certain specific diseases. This means that a person has borrowed antibodies in the blood and not those made by their own cells. This kind of immunity is called PASSIVE IMMUNITY. It lasts only as long as the antibodies last; when they are used up the immunity is gone.