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Lymph nodes are components of the lymphatic system. They are sometimes informally called lymph glands but, as they do not secrete substances, such terminology is not accurate. They are found throughout the body.
Lymph nodes are filters or traps for foreign particles and contain white blood cells.
Nodes act as filters, with an internal honeycomb of reticular connective tissue filled with lymphocytes that collect and destroy bacteria and viruses. When the body is fighting an infection, lymphocytes multiply rapidly and produce a characteristic swelling of the lymph nodes.
The lymph node is surrounded by a fibrous capsule, and inside the lymph node the fibrous capsule extends to form trabeculae. Thin reticular fibers form a supporting meshwork inside the node.
The parenchyma of the lymph node is divided into an outer cortex and an inner medulla.
In the cortex, the subcapsular sinus drains to cortical sinusoids.
The outer cortex and inner cortex have very different properties:
The cortex is absent at the hilum.
It is made out of the fluid from the blood called plasma.
There are two named structures in the medulla:
Shape and size
Human lymph nodes are bean-shaped and range in size from a few millimeters to about 1-2 cm in their normal state. They may become enlarged due to a tumor or infection. White blood cells are located within honeycomb structures of the lymph nodes. Lymph nodes are enlarged when the body is infected due to enhanced production of some cells and division of activated T and B cells. In some cases they may feel enlarged due to past infections; although one may be healthy, one may still feel them residually enlarged.
Lymph circulates to the lymph node via afferent lymphatic vessels and drains into the node just beneath the capsule in a space called the subcapsular sinus. The subcapsular sinus drains into trabecular sinuses and finally into medullary sinuses. The sinus space is criss-crossed by the pseudopods of macrophages which act to trap foreign particles and filter the lymph. The medullary sinuses converge at the hilum and lymph then leaves the lymph node via the efferent lymphatic vessel.
When a lymphocyte recognizes an antigen, B cells become activated and migrate to germinal centers (by definition, a "secondary nodule" has a germinal center, while a "primary nodule" does not). When antibody-producing plasma cells are formed, they migrate to the medullary cords. Stimulation of the lymphocytes by antigens can accelerate the migration process to about 10 times normal, resulting in characteristic swelling of the lymph nodes.
Humans have approximately 500-600 lymph nodes distributed throughout the body, with clusters found in the underarms, groin, neck, chest, and abdomen.
Lymph nodes of the human head and neck
Lymph nodes of the arm
These drain the whole of the arm, and are divided into two groups, superficial and deep. The superficial nodes are supplied by lymphatics which are present throughout the arm, but are particularly rich on the palm and flexor aspects of the digits.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Lymph_node". A list of authors is available in Wikipedia.|