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Parts of the Immune System
The immune system provides two levels of defense: innate and adaptive immunity. Both are discussed here along with as a brief description of the organs and tissues associated with the immune system.
Parts of the Immune System
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The immune system is like a police force. It patrols everywhere, and if it finds a disturbance, it calls for back-up. In this way, it is different from other systems in that it has to be able to react in any part of the body. The immune system provides two levels of defense: innate and adaptive immunity. This discussion will begin with a brief description of the organs and tissues associated with the immune system and then focus on the cells that provide innate and adaptive immunity.
Organs and tissues
Organs and tissues important to the proper functioning of the immune system include the thymus and bone marrow, lymph nodes and vessels, spleen, and skin.
Bone marrow and thymus
If the immune system is a police force, the bone marrow is the police academy because this is where the different types of immune system cells are created. All cells of the immune system are created in the bone marrow from a common type of starting cell, called a stem cell. These stem cells later develop into specific cell types, including red blood cells, platelets (important for blood clotting), and white blood cells (important for immune responses). The cell generation and differentiation process occurs every day for as long as we live. As a result, in the same way that the red blood cells in our blood are replenished after an injury or blood donation, our immune system cells are constantly replenished.
Some of the stem cells will become a type of immune system cell called a lymphocyte. Two types of lymphocytes comprise the adaptive immune system — B cells and T cells. B cells mature in the bone marrow (hence the name “B cell”). Cells that eventually become T cells travel from the bone marrow to the thymus by way of our bloodstream where they mature (hence the name “T cell”). The thymus is located just above the heart behind the sternum, or breastbone.
Lymph nodes and vessels
Lymph nodes are tissues full of immune cells. These nodes are located strategically throughout the body. Some are better known than others. For example, many people are familiar with tonsils and adenoids in the neck, but may not be aware of Peyer’s patches, which are lymph nodes that line the intestine. Numerous unnamed lymph nodes also exist throughout the body; in fact, virtually every corner of our body has some group of lymph nodes associated with it. Lymph nodes tend to be most prevalent in areas near body openings, such as the digestive tract and the genital region, because this is where pathogens most often enter the body.
If the immune system is a police force, lymph nodes are their stations. Once a pathogen is detected, nearby lymph nodes, often referred to as draining lymph nodes, become hives of activity, where cell activation, chemical signaling, and expansion of the number of immune system cells occur. The result is that the nodes increase in size and the surrounding areas may become tender as the enlarged nodes take up more space than usual. “Swollen glands” in the neck are an example that most of us have experienced. But, the same thing can occur anywhere lymph nodes are activated.
Two vessel systems are critical to the immune function of lymph nodes:
Blood vessels — Lymph, a fluid rich in immune system cells and signaling chemicals, travels from the blood into body tissues via capillaries. Lymphatic fluid collects pathogens and debris in the tissues. Then the lymphatic fluid containing immune cells enters draining lymph nodes where it is filtered. If pathogens are detected, immune system components are activated (see “adaptive immune system" section below for more about this).
Lymphatic vessels — Once filtration is complete, lymph vessels carry this fluid toward the heart. Depending on where the filtered lymph arrives from, it enters either the thoracic duct on the left side of the heart, or a similar, but smaller duct on the right side of the heart. The thoracic duct collects lymph from the whole body except the right side of the chest and head. The lymph from these areas drains to the smaller duct. From here, the lymph and its immune cells are returned to the bloodstream for another trip through the body.
The spleen is the largest internal organ of the immune system, and as such, it contains a large number of immune system cells. Indeed, about 25 percent of the blood that comes from the heart flows through the spleen on every beat. As blood circulates through the spleen, it is filtered to detect pathogens. As pathogens are detected, immune system cells are activated and increase in number to neutralize the pathogen. The spleen is particularly important in protecting people from bacterial infections, such as meningococcus and pneumococcus. So, while people can live without a spleen, it is important for them to be up to date on vaccines that protect against these infections because they are at greater risk of suffering from them.
Sometimes the skin is described as the largest organ of the immune system because it covers the entire body. People may not think about the skin as being part of this system, but the reality is that skin serves as an important physical barrier from many of the disease-causing agents that we come into contact with on a daily basis.
Reviewed on April 22, 2019
Immune System: Parts & Common Problems
Your immune system is a large network of organs, white blood cells, proteins (antibodies) and chemicals that work together to provide protection against infection, illness and disease.
A well-working immune system prevents germs from entering your body and kills them or limits their harm if they get in. To keep your immune system healthy, get plenty or sleep, stay active, eat healthy foods, keep your weight under control, reduce your stress and follow other healthful habits.
Your immune system is made of up a complex collection of cells and organs. The system works together to protect you from germs and helps you get better when you get sick.
What is the immune system?
Your immune system is a large network of organs, white blood cells, proteins (antibodies) and chemicals. This system works together to protect you from foreign invaders (bacteria, viruses, parasites, and fungi) that cause infection, illness and disease.
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What does the immune system do and how does it work?
Your immune system works hard to keep you healthy. Its job is to keep germs out of your body, destroy them or limit the extent of their harm if they get in.When your immune system is working properly: When your immune system is working properly, it can tell which cells are yours and which substances are foreign to your body. It activates, mobilizes, attacks and kills foreign invader germs that can cause you harm. Your immune system learns about germs after you’ve been exposed to them too. Your body develops antibodies to protect you from those specific germs. An example of this concept occurs when you get a vaccine. Your immune system builds up antibodies to foreign cells in the vaccine and will quickly remember these foreign cells and destroy them if you are exposed to them in the future. Sometimes doctors can prescribe antibiotics to help your immune system if you get sick. But antibiotics only kill certain bacteria. They don’t kill viruses.When your immune system is not working properly: When your immune system can’t mount a winning attack against an invader, a problem, such as an infection, develops. Also, sometimes your immune system mounts an attack when there is no invader or doesn’t stop an attack after the invader has been killed. These activities result in such problems as autoimmune diseases and allergic reactions.
What are the parts of the immune system?
Your immune system is made of up a complex collection of cells and organs. They all work together to protect you from germs and help you get better when you’re sick. The main parts of the immune system are:White blood cells: Serving as an army against harmful bacteria and viruses, white blood cells search for, attack and destroy germs to keep you healthy. White blood cells are a key part of your immune system. There are many white blood cell types in your immune system. Each cell type either circulates in your bloodstream and throughout your body or resides in a particular tissue, waiting to be called into action. Each cell type has a specific mission in your body’s defense system. Each has a different way of recognizing a problem, communicating with other cells on the defense team and performing their function.Lymph nodes: These small glands filter and destroy germs so they can’t spread to other parts of your body and make you sick. They also are part of your body’s lymphatic system. Lymph nodes contain immune cells that analyze the foreign invaders brought into your body. They then activate, replicate and send the specific lymphocytes (white blood cells) to fight off that particular invader. You have hundreds of lymph nodes all over your body, including in your neck, armpits, and groin. Swollen, tender lymph nodes are a clue that your body is fighting an infection.Spleen: Your spleen stores white blood cells that defend your body from foreign invaders. It also filters your blood, destroying old and damaged red blood cells.Tonsils and adenoids: Because they are located in your throat and nasal passage, tonsils and adenoids can trap foreign invaders (for example, bacteria or viruses) as soon as they enter your body. They have immune cells that produce antibodies to protect you from foreign invaders that cause throat and lung infections.Thymus: This small organ in your upper chest beneath your breast bone helps mature a certain type of white blood cell. The specific task of this cell is to learn to recognize and remember an invader so that an attack can be quickly mounted the next time this invader is encountered.Bone marrow: Stem cells in the spongy center of your bones develop into red blood cells, plasma cells and a variety of white blood cells and other types of immune cells. Your bone marrow makes billions of new blood cells every day and releases them into your bloodstream.Skin, mucous membranes and other first-line defenses: Your skin is the first line of defense in preventing and destroying germs before they enter your body. Skin produces oils and secretes other protective immune system cells. Mucous membranes line the respiratory, digestive, urinary and reproductive tracts. These membranes secrete mucus, which lubricates and moistens surfaces. Germs stick to mucus in the respiratory tract and then are moved out of the airways by hair-like structures called cilia. Tiny hairs in your nose catch germs. Enzymes found in sweat, tears, saliva and mucus membranes as well as secretions in the vagina all defend and destroy germs.