How Does the Immune System Work?

We know the immune system defends us from disease, but how does the immune system work?

Overview: How does the immune system work

The immune system is a highly specialized front-line defense that identifies, remembers, attacks and destroys disease-causing invaders or infected cells.

There are several types of immune cells, each possessing specific duties and characteristics. Several travel through the body killing foreign substances as they find them. Others patrol the gastrointestinal tract lining and blood vessels, safeguarding particular organs. The lymphatic system, which includes the lymph nodes, the spleen, bone marrow and thymus gland, produces these cells and transports them throughout the body. Lymph nodes and the spleen serve as filters designed to keep harmful organisms out of the blood stream. Most immune cells are produced in the bone marrow, the thymus or the spleen.

How does the immune system work to repel foreign invaders?

We are surrounded by billions of bacteria and viruses but getting into the human body is not an easy task!

The skin is thick and very hard to penetrate. In addition, the skin also produces a variety of substances that are harmful to invaders. Openings such as the eyes, nose, and mouth are protected by fluids or sticky mucus that capture harmful attackers. The respiratory tract also has mechanical defenses in the form of cilia, tiny hairs that remove particles. Intruders that get as far as the stomach are up against a sea of stomach acid that kills most of them.

But in spite of our fantastic defenses, hostile invaders still manage to get through. Some enter along with our food, while others may sneak in via the nose. And, as we all know, many things can break through our skin. In everyday life we often receive cuts or scrapes, and every time this happens we face the risk of a full-scale invasion from bacteria or viruses.

How does the immune system work when we get infected?

When we receive a cut, and when invaders enter the body, cells are destroyed. The dying cells trigger an automatic response called inflammation, which includes dilated blood vessels and increased blood flow. An inflammation is the body's equivalent to a burglar alarm. Once it goes off, it draws defensive cells to the damaged area in great numbers. Increased blood flow helps defensive cells reach the place where they're needed. It also accounts for the redness and swelling that occur.

The defensive cells are more commonly known as immune cells. They are part of a highly effective defense force called the immune system. The cells of the immune system work together with different proteins to seek out and destroy anything foreign or dangerous that enters our body. It takes some time for the immune cells to be activated - but once they're operating at full strength, there are very few hostile organisms that stand a chance.

Immune cells are white blood cells produced in huge quantities in the bone marrow. There are a wide variety of immune cells, each with its own strengths and weaknesses. Some seek out and devour invading organisms, while others destroy infected or mutated body cells. Yet another type has the ability to release special proteins called antibodies that mark intruders for destruction by other cells.

How does the immune system work to build immunity to a virus?

But the really cool thing about the immune system is that it has the ability to "remember" enemies that it has fought in the past. If the immune system detects a "registered" invader, it will strike much more quickly and more fiercely against it. As a result, an invader that tries to attack the body a second time will most likely be wiped out before there are any symptoms of disease. When this happens, we say that the body has become immune.

Learn more about the difference between acquired and natural immunity

How does the immune system work when dealing with bacteria and viruses?

Bacteria and viruses (our primary enemies) are the organisms most often responsible for attacking our bodies.

Most bacteria are free living, while others live in or on other organisms, including humans. Unfortunately, many bacteria that have human hosts produce toxins (poisons) that damage the body. Not all bacteria are harmful, though. Some are neutral and many are even desirable as they fulfill important functions in the body.

Bacteria are complete organisms that reproduce by cell division. Viruses, on the other hand, cannot reproduce on their own. They need a host cell. They hijack body cells of humans or other species, and trick them into producing new viruses that can then invade other cells. Frequently, the host cell is destroyed during the process.

In daily life we might speak of viruses, bacteria, and toxins. However, when reading about the immune system you’ll often come across the words antigen and pathogen. An antigen is a foreign substance that triggers a reaction from the immune system. Antigens are often found on the surfaces of bacteria and viruses. A pathogen is a microscopic organism that causes sickness. Hostile bacteria and viruses are examples of pathogens.

How does the immune system work: Complement system

The first part of the immune system that meets invaders such as bacteria is a group of proteins called the complement system. There are millions of different antibodies in your blood stream, each sensitive to a specific antigen. The complement proteins are activated by and work with (complement) the antibodies, hence the name. These proteins flow freely in the blood and can quickly reach the site of an invasion where they can react directly with antigens - molecules that the body recognizes as foreign substances. When activated, the complement proteins can
- trigger inflammation
- attract eater cells such as macrophages to the area
- coat intruders so that eater cells are more likely to devour them
- kill intruders

How does the immune system work: Phagocytes

Phagocytes is a group of immune cells specialized in finding and "devouring" bacteria, viruses, and dead or injured body cells. There are three main types, the granulocyte, the macrophage, and the dendritic cell.

The granulocytes often take the first stand during an infection. They attack any invaders in large numbers, and "eat" until they die. The pus in an infected wound consists chiefly of dead granulocytes.

The macrophages ("big eaters") are slower to respond to invaders than the granulocytes, but they are larger, live longer, and have far greater capacities. Macrophages also play a key part in alerting the rest of the immune system of invaders.

The dendritic cells are "eater" cells and devour intruders, like the granulocytes and the macrophages. They are also capable of filtering body fluids to clear them of foreign organisms and particles.

How does the immune system work in the lymphatic system?

The organs involved with the immune system are called the lymphoid organs. Lymphoid organs affect growth, development, and the release of lymphocytes. Lymphocytes is a type of infection fighting white blood cell which "patrol" the body for infectious microorganisms. Each lymphoid organ plays a role in the production and activation of lymphocytes.

White blood cells called lymphocytes, originate in the bone marrow but migrate to parts of the lymphatic system such as the lymph nodes, spleen, and thymus. There are two main types of lymphatic cells, T cells and B cells . The lymphatic system also involves a transportation system - lymph vessels - for transportation and storage of lymphocyte cells within the body. The lymphatic system feeds cells into the body and filters out dead cells and invading organisms such as bacteria.

On the surface of each lymphatic cell are receptors that enable them to recognize foreign substances. These receptors are very specialized - each can match only one specific antigen.

The lymphocyte cells travel through your body until they find an antigen of the right size and shape to match their specific receptors. It might seem limiting that the receptors of each lymphocyte cell can only match one specific type of antigen, but the body makes up for this by producing so many different lymphocyte cells that the immune system can recognize nearly all invaders.

In learning more on how does the immune system work, it is also important to understand how cells work in the immune system. To learn more about t-cells and b-cells, go to cells of the immune system.

How Does the Immune System Work: Conclusion

Our Creator has indeed provided us with a wonderful, complex and fascinating defense mechanism, preventing us from disease. For us to enjoy a healthy life, it is helpful and interesting to know a little bit on how does the immune system work.

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