The immune system is a wonderful thing and works hard to keep us healthy, but how much do you know about your immune system and how it works? This post will briefly outline some of the major parts of the immune system. I will be doing future posts about how the immune system works and how to keep it healthy, so watch for them.
What is the immune system?
First off, what is the immune system? Well a general definition I would use is a bodily system that protects the body from foreign substances and our own cells/tissues that are not working properly. So basically the immune system works to keep our body healthy by not only attacking foreign invaders like bacteria, viruses, toxins, and fungi, but also our own cells that are no longer functioning properly. And the immune system does this through something called the immune response.
In general the immune system is talked about in two major parts: innate immunity and acquired immunity. Innate immunity is the more basic part of the immune system. It is very fast-acting and recognizes very general characteristics of foreign substances. It also includes preventive measures such as barriers to keep bad stuff from getting into the body in the first place. Acquired immunity on the other hand is very precise and will recognize very specific parts of foreign substances. Acquired immunity takes more time to become fully activated than innate immunity, but it has a “memory” and can more quickly attack the same foreign invader in the future.
Parts of the immune system
Tissues & Organs
The immune system has many different parts that work together. The first part I like to talk about is often overlooked: the skin and mucous membranes. These make a good barrier to prevent foreign substances from entering the body. The mucous membranes are what line the respiratory and digestive tracts and act as a good barrier even while allowing the vital exchange of nutrients.
A very important part of the immune system is the bone marrow because this is where all the white blood cells originate in an adult. Without the white blood cells there would not be much of an immune response. This is why diseases like leukemia that affect the bone marrow can be so devastating.
Another important part of the immune system is the thymus. The thymus is located behind the top part of the breastbone and is a place where some white blood cells mature and learn to recognize and respond to foreign antigens rather than our own body or cells. The thymus is most active during childhood and tends to become less active as we get older, but is still an important part of the immune system none the less.
The lymph nodes, spleen, tonsils, and other lymphoid tissues are also key to the immune system and are basically places where white blood cells group together to watch for foreign substances. The lymph nodes also filter the lymph fluid as it makes its way back to the blood stream and the spleen filters the blood itself to help keep it free of foreign substances. Another significant function of the spleen is to break down old red blood cells that can no longer function properly so they will not cause problems throughout the body. The white blood cells in the tonsils help to track any foreign substances coming in through the mouth and nose. And finally, the other lymphoid tissues are found along the digestive tract and respond to foreign substances in the gut. So what is going on in the gut can actually have a significant impact on the immune system.
White Blood Cells
The white blood cells are vital to the immune response. Some white blood cells are considered part of innate immunity while others are part of acquired immunity. The white blood cells that are part of innate immunity include neutrophils, eosinophils, basophils, monocytes/macrophages, and natural killer cells, which all recognize general characteristics of foreign substances. Acquired immunity consists of the T-cells and B-cells, each which can be further divided into specific types according to what they do. The cells of acquired immunity recognize very specific parts of foreign substances and respond only to the specific antigen they are “coded” for.
The neutrophils are the most numerous circulating white blood cell and are very active during bacterial infections. They tend to be the first white blood cell to respond to an infection. The eosinophils and basophils tend to not play as big of a role in most typical infections, though the eosinophils respond to parasitic infections and the basophils play a part in allergies.
The monocytes/macrophages are the “big eaters” of the white blood cells. They are known as monocytes while they circulate in the blood and become macrophages when the leave the blood stream and enter into the tissues. Their main job is to “eat” foreign substances and digest them. They also help to clean up fragments of damaged tissues and cells.
The natural killer cells have a very important function in fighting viral infections. Viruses “take over” cells and force them to make more viruses and other substances for the virus. Natural killer cells recognize the cells that have been “taken over” and attack and kill them. Natural killer cells also have an essential role in killing tumor cells.
The T-cells are crucial in the immune response. There are two main types of T-cells: helper T-cells and cytotoxic T-cells. The cytotoxic T-cells are the ones that become active and attack foreign substances. The helper T-cells are very important and help basically “ramp up” the immune response to work properly. To give you an idea of how important helper T-cells are to the immune system, they are the ones affected by HIV and when the number of them becomes too low you begin to get all the terrible effects of AIDS.
The B-cells are the white blood cells that produce antibodies. The antibodies go into the blood and attach to foreign substances and sometimes inactivate them directly, but often the antibodies stick to foreign substances and make them easier to be recognized and attacked by other white blood cells.
Complement System
There is one more part of the immune system that I want to talk about and that is the complement system. Complement is actually a set of proteins that circulate in the blood and are normally inactive. However, when they come in contact with some foreign substances or antibodies attached to a foreign invader the proteins are changed and become active and result in a cascade of events activating even more proteins in the system. These activated proteins result in several actions. Some of the proteins act as signals for inflammation and also bring more white blood cells to the area. Some of the proteins will attach to the surface of the foreign substance and make it more readily recognized by some other white blood cells. And then some of the proteins will even come together and form a protein that can basically poke holes in the cell membrane of some foreign invaders.
Now the complement system is interesting in that it plays a part in both innate immunity and acquired immunity. It can be activated directly by recognizing general characteristics of foreign invaders, but also can be activated by antibodies, which are part of acquired immunity.
Conclusion
The immune system is an amazing and complex system that does a wonderful job of keeping us healthy. One post is not enough to cover much about the immune system and this post only briefly explained some of the major parts of the immune system. Coming up after Christmas, we’ll look at how all the parts of the immune system work together to keep you healthy. After that, you’ll want to catch our blog on how to keep the immune system healthy.
