Lymph node

A Lymph node (]

Medulla

There are two named structures in the medulla:
* The "medullary cords" are cords of lymphatic tissue, and include plasma cells and B cells
* The "medullary sinuses" (or "sinusoids") are vessel-like spaces separating the medullary cords. The Lymph flows into the medullary sinuses from cortical sinuses, and into efferent lymphatic vessels. Medullary sinuses contain histiocytes (immobile macrophages) and reticular cells.

hape 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.

Lymphatic circulation

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" towards either a more central lymph node or ultimately for drainage into a central venous subclavian blood vessel, most via Virchow's node and Ductus Thoracicus. Valves on the afferent side prevent backflow.

Lymphocytes, both B cells and T cells, constantly circulate through the lymph nodes. They enter the lymph node via the postcapillary venules, and cross its wall by the process of diapedesis.
* The B cells migrate to the nodular cortex and medulla.
* The T cells migrate to the deep cortex ("paracortex").

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.

The spleen and tonsils are large lymphoid organs that serve similar functions to lymph nodes, though the spleen filters blood cells rather than lymph.

Distribution

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

* Cervical lymph nodes
**Anterior cervical: These nodes, both superficial and deep, lie above and beneath the sternocleidomastoid muscles. They drain the internal structures of the throat as well as part of the posterior pharynx, tonsils, and thyroid gland.
** Posterior cervical: These nodes extend in a line posterior to the sternocleidomastoids but in front of the trapezius, from the level of the Mastoid portion of the temporal bone to the clavicle. They are frequently enlarged during upper respiratory infections.

* Tonsillar: (sub mandibular) These nodes are located just below the angle of the mandible. They drain the tonsillar and posterior pharyngeal regions.

* Sub-mandibular: These nodes run along the underside of the jaw on either side. They drain the structures in the floor of the mouth.

* Sub-mental: These nodes are just below the chin. They drain the teeth and intra-oral cavity.

* Supraclavicular lymph nodes: These nodes are in the hollow above the clavicle, just lateral to where it joins the sternum. They drain a part of the thoracic cavity and abdomen. Virchow's node is a left supraclavicular lymph node which receives the lymph drainage from most of the body (especially the abdomen) via the thoracic duct and is thus an early site of metastasis for various malignancies.

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.

* Superficial lymph glands of the arm:
** supratrochlear glands: Situated above the medial epicondyle of the humerus, medial to the basilic vein, they drain the C7 and C8 dermatomes.
** deltoideopectoral glands: Situated between the pectoralis major and deltoid muscles inferior to the clavicle.

* Deep lymph glands of the arm: These comprise the axillary glands, which are 20-30 individual glands and can be subdivided into:
** lateral glands
** anterior or pectoral glands
** posterior or subscapular glands
** central or intermediate glands
** medial or subclavicular glands

Lower limbs

* Superficial inguinal lymph nodes
* Deep inguinal lymph nodes

Pathology

Lymphadenopathy is a term meaning "disease of the lymph nodes." It is, however, almost synonymously used with "swollen/enlarged lymph nodes". In this case, the lymph nodes are palpable, and is a sign of various infections and diseases.

=Additional

References

ee also

*Adenitis
*Lymphadenectomy
*Lymphoma
*List of hæmatological diseases and malignancies

External links

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