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Lymph nodes are small oval-shaped balls of lymphatic tissue, distributed widely throughout the body and linked by lymphatic vessels.
Describe the structure and function of lymph nodes
Lymph nodes are well distributed around the chest, armpits, neck, and abdomen.
Each lymph node is surrounded by a fibrous capsule, which encircles the internal cortex and medulla. The cortex is mainly composed of clusters of B and T cells. The medulla contains plasma cells, macrophages, and B cells, as well as sinuses, which are vessel-like spaces that the lymph flows into, and nodules that are located within the sinuses.
Lymph nodes contain a hilium beneath the capsule, which brings blood supply to the tissues of the lymph node.
Antigen presentation by dendritic cells occurs in the lymph nodes, which triggers an adaptive immune respeonse.
small oval bodies of the lymphatic system, that act as filters, with an internal honeycomb of connective tissue filled with lymphocytes and macrophages that collect and destroy bacteria, viruses, and foreign matter from lymph.
Lymph nodes are small oval-shaped balls of lymphatic tissue, distributed widely throughout the body and linked by a vast network of lymphatic vessels. Lymph nodes are repositories of B cells, T cells, and other immune system cells, such as dendritic cells and macrophages. They act as filters for foreign particles in the body and are one of the sites where adaptive immune responses are triggered.
Structure of Lymph Nodes
Lymph nodes are found throughout the body, and are typically 1-2 cm long. Humans have approximately 500-600 lymph nodes, with clusters found in the underarms, groin, neck, chest, and abdomen. Each lymph node is surrounded by a fibrous capsule, which encircles the internal cortex and medulla . The cortex is mainly composed of clusters of B cells in the outer layers and T cells in the inner layers, and may contain antigen presenting dendritic cells as well. The medulla contains plasma cells, macrophages, and B cells, as well as sinuses, which are vessel-like spaces that the lymph flows into. Inside each sinus cavity is a nodule, which are smaller, denser bundles of lymphoid tissue that usually contain germinal centers, which are the sites of B cell proliferation during antigen presentation. The sinuses are partially divided by capsule tissue, which causes lymph fluid to flow around the nodules in each sinus cavity on their way through the node.
Lymph fluid flows into and out of the lymph nodes via the lymphatic vessels, a network of valved vessels that are similar in structure to cardiovascular veins. Each lymph node has an afferent lymph vessel, which directs lymph into the node, and an efferent lymph vessel, which directs lymph out of the node at the concave side of the node, known as the hilum. The hilium also contains the blood supply of the lymph node.
Function of Lymph Nodes
Lymph nodes are the primary site for antigen presentation and activation in an adaptive immune response in B and T lymphocytes. These lymphocytes are continuously recirculated through the lymph nodes and the bloodstream. Molecules found on bacteria cell walls, or the cell walls of virally infected cells or even chemical substances and toxins secreted from bacteria, called antigens, may be taken up by cells into the lymph system and then into lymph nodes. Then, antigen presenting cells called dendritic cells present the antigen molecule to naive B and T lymphocytes, that then undergo cell cycle proliferation into lymphocytes that are able to specifically detect and eliminate pathogens associated with that antigen, through a variety of ways, such as cytotoxic action (T cells) and antibody production (B cells).
Besides adaptive immunity, the lymph nodes also filter the lymph fluid. Macrophages in the sinus spaces will phagocytize (engulf) foreign particles, such as pathogens, so that the lymph fluid that returns to the bloodstream is cleaned of problematic abnormalities. The lymph node is also arranged in such a way that the chance of B and T lymphocytes encountering dendritic cells is quite high, in order to facilitate antigen presentation.
Lymphadenopathy describes the condition when lymph nodes are swollen. The changes observed in lymph nodes have clinical significance. The primary reason that they swell is simply increased flow of lymph into lymph nodes, which may carry a higher amount of debris, so inflammation occurs as more neutrophils, and later macrophages enter the node to remove debris from the lymph.
Lymphadenopathy is a symptom in various conditions, which may range from trivial, such as a common cold or a minor infection, to life-threatening, such as many cancers or severe infections. Cancers that have become very severe and widespread from frequent metastases tend to have lymphadenopathy, so cancer staging criteria will include lymph node involvement. Additionally, cancers like lymphomas, which have tumors made out of abberrant lymphocytes will nearly always show lymphadenopathy, which are often early warning signs for this type of cancer.