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- lymphoid tissue
- king’s evil
- lymph nodule
lymph node
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What is a lymph node?
Lymph nodes are small, bean-shaped masses of lymphoid tissue enclosed by connective tissue that occur with lymphatic vessels. As part of the lymphatic system, they filter blood and provide specialized tissues where foreign antigens can be trapped and exposed to immune system cells for destruction. Lymph nodes are typically concentrated near junctions of major lymphatic vessels, most prominently in the neck, groin, and armpits. Each lymph node is divided into the capsule and the cortex, with the cortex further divided. Lymphocytes enter through high endothelial venules, and structural divisions serve different purposes.
Lymph nodes are critical to the immune system but vulnerable to cancer as cancerous cells spread and become trapped there, complicating treatment.
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Where in the body are lymph nodes found?
Lymph nodes are small, bean-shaped masses of lymphoid tissue that filter blood and trap foreign antigens, which are then exposed to immune system cells for destruction. These nodes are found throughout the body along lymphatic routes and are concentrated near major lymphatic vessel junctions. They are especially prevalent in the neck (cervical nodes), groin (inguinal nodes), and armpits (axillary nodes). Lymph nodes are also found near the knees (popliteal nodes).
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What do lymph nodes do in the body?
Lymph nodes are small, bean-shaped masses of lymphoid tissue that filter blood and trap foreign antigens. As part of the lymphatic system, they activate the immune system by exposing trapped antigens to immune cells for destruction.
Lymph nodes are divided into the capsule, cortex, and medulla. Lymph and cells enter through afferent lymphatic vessels, while lymphocytes enter through specialized blood vessels. Structural divisions support the recognition of foreign agents. B cells form follicles, and T cells remain in the paracortex. Activated lymphocytes migrate through the medulla and enter circulation.
Lymph nodes filter microorganisms, but this function makes them vulnerable to cancer as they can trap and concentrate metastasizing cancerous cells. Lymph is a pale fluid bathing tissues, maintaining fluid balance, and removing bacteria. It contains lymphocytes and macrophages, filtering through lymphatic organs and nodes.
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What are the main parts or structures of a lymph node?
Lymph nodes are masses of lymphoid tissue that filter blood and trap foreign antigens, which are then exposed to immune system cells for destruction.
The main structural parts of a lymph node:
* Capsule An outer layer of connective tissue
* Cortex Contains B and T lymphocytes, dendritic cells, and macrophages. It divides into the outer cortex and inner cortex, or paracortex.
* Medulla Consists primarily of activated antibody-secreting plasma cells.Lymph and its cells enter through afferent lymphatic vessels, while lymphocytes enter through high endothelial venules (HEVs). Structural divisions support the migration of lymphocytes to effectively recognize foreign agents. B cells form follicles in the outer cortex, while T cells remain in the paracortex. Activated lymphocytes migrate through the medulla and exit via the efferent lymphatic vessel.
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How do lymph nodes help fight infections?
Lymph nodes are masses of lymphoid tissue that filter blood and trap foreign antigens, which are then exposed to immune system cells for destruction. Lymph and associated cells enter through afferent lymphatic vessels, while lymphocytes enter through specialized blood vessels.
Within lymph nodes, lymphocytes migrate to recognize foreign agents. B cells form follicles, and after encountering an antigen, they become activated. T cells remain in the paracortex, where macrophages and dendritic cells present antigenic peptides, stimulating them to become helper T cells or cytotoxic T lymphocytes. Activated lymphocytes migrate through the medulla and enter lymphatic circulation. This filtration process and immune response are critical, but can also make lymph nodes vulnerable to cancer.
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How do lymph nodes change when the body has an infection or disease?
Lymph nodes, crucial for immune defense, change significantly during infection or disease. As filters for the lymphatic system, they trap bacteria, allergenic particles, and cancerous cells.
When foreign invaders enter the body, they are carried into the lymph nodes, stimulating lymphocyte proliferation. This proliferation leads to the enlargement of the nodes, a common sign of infection. Some lymphocytes remain in the node, while others migrate to other nodes elsewhere in the body, producing antibodies or directly attacking the foreign material.
Conditions such as syphilis, infectious mononucleosis, amyloidosis, tuberculosis, lymphocytic leukemia, and lymphoma can cause lymph node enlargement. Cancerous cells spreading through metastasis can also become trapped in lymph nodes, leading to their proliferation and complicating treatment. Interference with lymphatic flow can cause fluid accumulation in tissues, resulting in tissue swelling known as lymphedema.
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lymph node, any of the small, bean-shaped masses of lymphoid tissue enclosed by a capsule of connective tissue that occur in association with the lymphatic vessels. As part of the lymphatic system, lymph nodes serve as filters for the blood, providing specialized tissues where foreign antigens can be trapped and exposed to cells of the immune system for destruction. They are typically found concentrated near junctions of the major lymphatic vessels, most prominently in the neck, groin, and armpits.
Each lymph node is divided into two general regions, the capsule and the cortex. The capsule is an outer layer of connective tissue. Underlying the capsule is the cortex, a region containing mostly inactivated B and T lymphocytes plus numerous accessory cells such as dendritic cells and macrophages. The cortex is further divided into two functional areas: the outer cortex and inner cortex, or paracortex. These regions surround an inner medulla, which consists primarily of activated antibody-secreting plasma cells.
Cells enter the lymph node through two primary routes. Lymph and its associated cells enter through the afferent lymphatic vessels, which drain into each node through its convex surface. These vessels may drain directly from the lymphatic capillaries, or they may be connected to a previous node. Lymphocytes generally enter through specialized blood vessels called high endothelial venules (HEVs). HEVs contain a single layer of large endothelial cells that possess surface receptors specific for B and T lymphocytes. As these cells pass through the HEVs, they bind to the receptors and are carried into the paracortex of the lymph node.
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The structural divisions within a lymph node serve different purposes. Most of the lymphocytes within a node are “naive”—i.e., they have yet to encounter antigen—and therefore must migrate to regions where they will be most effective in recognizing foreign agents. B cells enter the paracortex through the HEVs and then migrate into the outer cortex and join specialized dendritic cells and macrophages to form follicles. Primary follicles consist of a resting B cell surrounded by a loose network of dendritic cells. After encountering a foreign antigen, the B cell becomes activated and is surrounded by a more tightly packed association of dendritic cells and macrophages, forming a germinal centre. The germinal centre in turn is enclosed by a mantle zone—a ring of resting B cells and dendritic cells. The germinal centre and mantle together compose a secondary follicle, which is the site of antigen-dependent B-cell maturation. The activated B cells then migrate through the paracortex to the medulla, where they proliferate as antibody-secreting plasma cells. T cells enter the lymph node through the HEVs and remain in the paracortex, where the cortical macrophages and dendritic cells present antigenic peptides to the naive T cells, stimulating them to become activated helper T cells or cytotoxic T lymphocytes. All activated lymphocytes migrate through the medulla and enter the lymphatic circulation through the efferent lymphatic vessel, which drains either into adjacent lymph nodes or ultimately into the thoracic duct, a major vessel of the lymphatic system.
The central role played by lymph nodes in filtering microorganisms and other undesired substances from the blood is critical to the functioning of the immune system but also makes lymph nodes vulnerable to cancer. As cancerous cells spread by metastasis, they can become trapped and concentrated in lymph nodes, where they proliferate. Virtually all cancers have the potential of spreading to lymph nodes, a condition that greatly complicates treatment. In most cases surgery alone will not remove the cancer from the nodes, and therefore postoperative radiation or chemotherapy is required.