This system transports lymph throughout the body. Lymph is formed from fluid that seeps through the thin walls of capillaries into the body's tissues. This fluid contains oxygen, proteins, and other nutrients that nourish the tissues. Some of this fluid reenters the capillaries and some of it enters the lymphatic vessels becoming lymph. Small lymphatic vessels connect to larger ones and eventually form the thoracic duct.
The thoracic duct is the largest lymphatic vessel. It joins with the subclavian vein and thus returns lymph to the bloodstream. Lymph also transports foreign substances such as bacteria , cancer cells, and dead or damaged cells that may be present in tissues into the lymphatic vessels and to lymph nodes for disposal. Lymph contains many white blood cells. All substances transported by the lymph pass through at least one lymph node, where foreign substances can be filtered out and destroyed before fluid is returned to the bloodstream.
In the lymph nodes, white blood cells can collect, interact with each other and with antigens, and generate immune responses to foreign substances.
Lymph nodes contain a mesh of tissue that is tightly packed with B cells, T cells, dendritic cells, and macrophages. Harmful microorganisms are filtered through the mesh, then identified and attacked by B cells and T cells.
Lymph nodes are often clustered in areas where the lymphatic vessels branch off, such as the neck, armpits, and groin. These organs trap microorganisms and other foreign substances and provide a place for mature cells of the immune system to collect, interact with each other and with the foreign substances, and generate a specific immune response.
The lymph nodes are strategically placed in the body and are connected by an extensive network of lymphatic vessels—the lymphatic system Overview of the Lymphatic System The lymphatic system is a vital part of the immune system.
It includes organs such as the thymus, bone marrow, spleen, tonsils, appendix, and Peyer patches in the small intestine that produce The lymphatic system transports microorganisms, other foreign substances, cancer cells, and dead or damaged cells from the tissues to the lymph nodes, where these substances and cells are filtered out and destroyed.
Then the filtered lymph is returned to the bloodstream. Lymph nodes are one of the first places that cancer cells can spread.
Thus, doctors often evaluate lymph nodes to determine whether a cancer has spread. Cancer cells in a lymph node can cause the node to swell. Lymph nodes can also swell after an infection because acquired immune responses to infections are generated in lymph nodes. Sometimes lymph nodes swell because bacteria that are carried to a lymph node are not killed and cause an infection in the lymph node lymphadenitis. Lymph nodes contain a mesh of tissue where harmful microorganisms and dead or damaged cells are filtered out and destroyed.
To be able to destroy invaders, the immune system must first recognize them. That is, the immune system must be able to distinguish what is nonself foreign from what is self. The immune system can make this distinction because all cells have identification molecules antigens on their surface.
Microorganisms are recognized because the identification molecules on their surface are foreign. HLA molecules are called antigens because if transplanted, as in a kidney or skin graft, they can provoke an immune response in another person normally, they do not provoke an immune response in the person who has them. Each person has an almost unique combination of HLAs. The immune system then attacks that cell. HLA molecules are what doctors try to match when a person needs an organ transplant.
Some white blood cells—B cells B lymphocytes —can recognize invaders directly. But others—T cells T lymphocytes —need help from cells called antigen-presenting cells:. The antigen-presenting cell then combines antigen fragments from the invader with the cell's own HLA molecules. A T cell with a matching receptor on its surface can attach to part of the HLA molecule presenting the antigen fragment, as a key fits into a lock.
T cells are part of the immune surveillance system. They travel through the bloodstream and lymphatic system. When they reach the lymph nodes or another secondary lymphoid organ, they look for foreign substances antigens in the body.
However, before they can fully recognize and respond to a foreign antigen, the antigen must be processed and presented to the T cell by another white blood cell, called an antigen-presenting cell. Antigen-presenting cells consist of dendritic cells which are the most effective , macrophages, and B cells. White blood cells are activated when they recognize invaders. For example, when the antigen-presenting cell presents antigen fragments bound to HLA to a T cell, the T cell attaches to the fragments and is activated.
B cells can be activated directly by invaders. Once activated, white blood cells ingest or kill the invader or do both. Usually, more than one type of white blood cell is needed to kill an invader. Immune cells, such as macrophages and activated T cells, release substances that attract other immune cells to the trouble spot, thus mobilizing defenses.
The invader itself may release substances that attract immune cells. The immune response must be regulated to prevent extensive damage to the body, as occurs in autoimmune disorders Autoimmune Disorders An autoimmune disorder is a malfunction of the body's immune system that causes the body to attack its own tissues. Regulatory suppressor T cells help control the response by secreting cytokines chemical messengers of the immune system that inhibit immune responses.
These cells prevent the immune response from continuing indefinitely. Resolution involves confining the invader and eliminating it from the body. After the invader is eliminated, most white blood cells self-destruct and are ingested. Those that are spared are called memory cells. The body retains memory cells, which are part of acquired immunity, to remember specific invaders and respond more vigorously to them at the next encounter.
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This site complies with the HONcode standard for trustworthy health information: verify here. Common Health Topics. Components of the Immune System. Lines of Defense. Physical barriers White blood cells Molecules Lymphoid organs.
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Lung inflammation caused by inhaled toxicants: a review. Int J of Copd. Molecular basis of chronic inflammation in lung diseases: new therapeutic approach. Int J Copd. Ernandez T, Mayadas TN. The Changing Landscape of Renal Inflammation. Trends Mol Med. Infection refers to the invasion and multiplication of bacteria or viruses within the body, while inflammation is the body's protective response against infection. Inflammation is a complex cellular process involving various types of immune cells, clotting proteins and signaling molecules.
It can occur after an injury, such as a burn or a cut, and also when there is an infection present in the body. But, inflammation can sometimes also occur without an injury or infection. Sometimes, the immune system can over-react and can cause inflammation by attacking healthy tissues within the body. When auto-inflammation occurs, there is a dysfunction within the immune system that triggers the body to mount an inflammatory response against itself.
It is not known why this occurs, but it is thought that a virus or another trigger in the environment may be the initial cause. When an injury occurs, the cells of our immune system immediately travel to the site of injury or irritation and the inflammatory response begins.
This includes widening of local blood vessels to allow fluid and immune cells into surrounding injured tissue, which causes swelling, redness, warmth and pain at the site. This process protects the injured area and signals other cells to the site to begin repairing and healing the injury. Normally, inflammation slowly goes away after the irritation has been removed and the body is adequately protected, as can be seen with the example of the splinter in the skin.
During auto-inflammation, cells of the immune system also travel to certain sites in the body. However, there are no injuries or infections at these sites. Instead of repairing and healing, the auto-inflammatory response often ends up harming healthy tissues. Auto-inflammation can cause damage and destruction to the body tissues or organs that it affects. An auto-inflammatory event can be a one-time occurrence or it may develop into a chronic long-term issue.
The exact cause of auto-inflammatory conditions is not known. A dysfunction of the immune system causes auto-inflammation, but it is unknown why this dysfunction occurs. Various theories include exposure to a virus, possible environmental triggers, and genetics. The immune system is a cellular system within the body. White blood cells, also known as leukocytes, make up a large part of the cells of the immune system.
White blood cells help fight infection by attacking invaders and consuming infected or dead cells. The body has various types of white blood cells, all of which are produced in the bone marrow the soft middle part of our bones.
People with auto-inflammatory conditions may have higher levels of white blood cells in their blood, or they may have white blood cells present where white blood cells are not normally present. If your child has symptoms of auto-inflammation or a suspected auto-inflammatory disease, several tests may be completed including a physical exam, imaging tests such as magnetic resonance imaging MRI , a biopsy, a lumbar puncture and other tests including blood, urine or stool tests.
Children with auto-inflammatory diseases are typically treated with immune-modifying therapies or immunosuppressant treatments.
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