A lymph node or (wrongly) a lymph gland is a "filter station" for the lymph (tissue water) and belongs to the lymphatic system . Each lymph node is responsible for absorbing and filtering the lymph from one region of the body. This filtered area is called the tributary area , the lymph node is the regional lymph node of this area. Lymph nodes belong to the defense system ( immune system ) of an organism. People have 300 to 700 lymph nodes. They are found in all mammals , in primitive form also in birds .
Latin synonyms are: Nodus lymphoideus , Nodus lymphaticus , Nodus lympharis (abbreviation Nodus lymphaticus = Nl. , Plural Nodi lymphatici = Nll. ) Or Lymphonodus (abbreviation Ln. , Plural Lnn. ). The term lymph comes from the Latin lympha "spring water".
Lymph nodes in humans are usually around 5–10 mm in size and oval or irregularly shaped; in the groin and neck they can also be up to 20 mm in size. If they are larger than 2 cm and take on a spherical shape, then they are activated and engaged in the defense against diseases. In animals, lymph nodes can fuse into very large structures. For example, the knee fold lymph node in cattle is up to 11 cm long and 2 cm thick.
Layout and function
A lymph node is surrounded by a capsule from which connective tissue septa (trabeculae) pull into the interior. The functional tissue inside is a lymphoreticular tissue . It consists of reticular cells and free cells ( lymphocytes , antigen-presenting cells ). The lymphoreticular tissue of the lymph node is divided into three areas, in which the lymphocytes "mature" immunologically on foreign proteins :
- In the cortex ( cortex nodi lymphoidei ) the lymphocytes are organized into cortical follicles ( lymph nodes ). They serve to multiply and differentiate the B-lymphocytes.
- In the medulla , the lymphoreticular tissue is stored in strands.
- There is a transition zone ( paracortex ) between the cortex and the pith . This is where the T-lymphocytes multiply.
The reticular cells form a three-dimensional meshwork in the lymph node, the cavities of which are known as the lymphatic sinus . This is subdivided into the marginal sinus located under the capsule, the medullary sinus located in the area of the marrow and the intermediate sinus located in between.
The lymph from the catchment area of the lymph node is called the primary lymph . It passes through the afferent lymphatic vessels ( Vasa lymphatica afferentia , Singular Vas lymphaticum afferens ) through the capsule and primarily flows through the sinus system. The sinus wall cells and macrophages undergo nonspecific phagocytosis . A small part of the primary lymph seeps into the lymphatic tissue and, in the presence of antigens, stimulates the differentiation of lymphocytes. The differentiated T, plasma and memory cells that are created in this way end up in the lymph, which then becomes a secondary lymph . At the exit port ( hilum or hilus ), the secondary lymph is drained through a draining lymphatic vessel ( vas lymphaticum efferens ). This secondary lymph often also flows through other lymph nodes, which are known as collecting lymph nodes.
In the lymph nodes of pigs , the relationships between the pulp, bark, vessels and thus the current path are reversed. The afferent vessel passes through the hilum, the medulla is peripheral, the cortex is centrally located, and the efferent vessels exit the lymph node through the capsule.
The main regions with lymph nodes
- behind the ear: Lymphonodi retroauriculares
- below the ear: parotid lymph nodes ( Lnn. parotidei or Lnn. prauriculares )
- on the occiput: occipital lymph node ( Lnn. occipitales )
- on the face: facial lymph nodes ( Nll. faciales )
- on the lower jaw: lower jaw lymph nodes ( Lnn. submandibulares )
- on the chin: chin lymph nodes ( Lnn. submentales )
- in the armpit: axillary lymph nodes
- Lower extremity: popliteal lymph nodes
Lymph nodes located on the surface can be felt with the fingers. Ultrasound , computed tomography (CT), magnetic resonance imaging (MRT), lymphography and scintigraphy (see sentinel lymph nodes ) are used for more precise examinations and the representation of deep lymph nodes .
The anatomical structure of the lymph node can be shown in the ultrasound and shows a fatty, hypoechoic hilum as normal finding. In the case of non-specific, reactive changes in the lymph nodes, this hilar sign is emphasized and the lymph node retains its oval shape. A lack of the hilar sign can indicate infiltration by a malignancy. Hypervascularization can be seen in both reactive and malignant lymph nodes. A loss of the oval shape in favor of a circular shape of the lymph node can also indicate malignant infiltration. Necroses in the lymph nodes are often anechoic and can result from both abscessing infections and the melting of a tumor.
In diseases in the tributary area, foreign cells and particles get into the regional lymph nodes and a reaction occurs. The area in front of it (more peripheral) in the direction of the flow must then be regarded as the location of the disease. Antigens trigger the multiplication of B and T lymphocytes . As a result, the lymph node swells up ( lymphadenopathy , pathological lymph node swelling) and is usually only noticed through this ( lymphadenitis or lymphoma ). Activated lymph nodes have a widened dark border in the ultrasound image and there is increased blood flow. The lymph nodes that are primarily responsible for a specific organ are also known as sentinel lymph nodes . In the case of cancer, these are examined first. If there are no cancer cells in them, it is assumed that no metastases have spread via the lymphatic system.
In 2018, it was shown in mice that cancer cells implanted in lymph nodes can migrate into blood vessels within 3 days, faster than previously assumed, and thus reach other organs and cause metastases there.
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