25.7
Structure et fonctions détaillées des ganglions lymphatiques
Les ganglions lymphatiques sont des structures en forme de haricot, situés le long des vaisseaux lymphatiques dans les régions inguinale, axillaire et…
Les ganglions lymphatiques sont de petites structures en forme de haricot qui se regroupent le long des vaisseaux lymphatiques. Ils sont principalement situés dans les régions inguinale, axillaire et cervicale.
Ces ganglions ont une enveloppe extérieure appelée capsule, qui prolonge les trabécules vers l’intérieur, divisant le nœud en compartiments.
Histologiquement, chaque ganglion lymphatique peut être divisé en cortex superficiel et médullaire profond.
Le cortex comprend des cellules dendritiques, des macrophages et des follicules densément emballés de lymphocytes B. Lors de la présentation de l’antigène par les cellules dendritiques, les lymphocytes B se transforment en plasmocytes producteurs d’anticorps et en lymphocytes B mémoire.
Le cortex interne est principalement constitué de lymphocytes T migrés du cortex. Il contient également des cellules dendritiques, qui peuvent activer les lymphocytes T.
La lymphe pénètre dans les ganglions lymphatiques via les lymphatiques afférents et circule dans les sinus remplis de fibres réticulaires, de lymphocytes et de macrophages.
La lymphe est filtrée à l’intérieur de ces sinus. Les macrophages éliminent les substances étrangères par phagocytose, tandis que les lymphocytes détruisent les agents pathogènes en utilisant des réponses immunitaires.
La lymphe filtrée quitte le ganglion lymphatique via les lymphatiques efférents et émerge de l’autre extrémité du ganglion au niveau du hile.
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Q1: What are the main structural regions within a lymph node?
Lymph nodes contain two primary histological regions: the superficial cortex and the deep medulla. The cortex houses dendritic cells, macrophages, and densely packed B lymphocyte follicles. The inner cortex consists mainly of T lymphocytes and dendritic cells. The medulla contains activated B and T lymphocytes that distribute throughout the body after immune activation.
Q2: How do B lymphocytes mature within lymph nodes?
When dendritic cells present antigens to B lymphocytes in the cortex, the B cells mature into antibody-producing plasma cells and memory B cells. These activated cells then enter the medulla, where they are distributed throughout the body. This process enables the adaptive immune response to foreign substances.
Q3: What is the path lymph takes through a lymph node?
Lymph enters via multiple afferent lymphatic vessels at the node's convex surface and flows into the subcapsular sinus beneath the capsule. It then travels through trabecular sinuses parallel to the trabeculae and into medullary sinuses. Finally, lymph exits through one or two broader efferent lymphatic vessels at the hilum.
Q4: How do lymph nodes filter pathogens and foreign substances?
Sinuses within lymph nodes contain reticular fibers, lymphocytes, and macrophages that trap foreign substances. Macrophages eliminate pathogens through phagocytosis, while lymphocytes destroy them using immune responses. The slow lymph flow through multiple sinuses allows extended filtration time before lymph returns to the blood.
Q5: Why does lymph flow slowly through lymph nodes?
Multiple afferent vessels bring lymph into each node, but only one or two efferent vessels carry it out. This structural arrangement creates a bottleneck that slows lymph transit through the node. The reduced flow rate allows more time for immune cells and macrophages to filter and eliminate pathogens before lymph returns to circulation.
Q6: Where are lymph nodes located in the body?
Lymph nodes are small, bean-shaped structures that cluster along lymphatic vessels in three major regions: the inguinal nodes in the groin, axillary nodes in the armpits, and cervical nodes in the neck. These strategic locations allow lymph nodes to monitor and filter lymph from different body areas.
Q7: What role do dendritic cells play in lymph node function?
Dendritic cells in the cortex present antigens to B lymphocytes, triggering their maturation into plasma cells and memory B cells. In the inner cortex, dendritic cells activate T lymphocytes. These antigen-presenting functions enable lymph nodes to coordinate adaptive immune responses against pathogens.