25.7
Struttura dettagliata e funzioni dei linfonodi
I linfonodi sono strutture a forma di fagiolo che si raggruppano lungo i vasi linfatici nelle regioni inguinale, ascellare e cervicale. Ogni nodo è di…
I linfonodi sono piccole strutture a forma di fagiolo che si raggruppano lungo i vasi linfatici. Si trovano principalmente nelle regioni inguinale, ascellare e cervicale.
Questi nodi hanno un rivestimento esterno chiamato capsula, che estende le trabecole verso l'interno, dividendo il nodo in compartimenti.
Istologicamente, ogni linfonodo può essere suddiviso in corteccia superficiale e midollo profondo.
La corteccia comprende cellule dendritiche, macrofagi e follicoli densamente impacchettati di linfociti B. Dopo la presentazione dell'antigene da parte delle cellule dendritiche, i linfociti B maturano in plasmacellule produttrici di anticorpi e cellule B di memoria.
La corteccia interna è costituita principalmente da linfociti T migrati dalla corteccia. Contiene anche cellule dendritiche, che possono attivare i linfociti T.
La linfa entra nei linfonodi attraverso i linfatici afferenti e scorre attraverso i seni pieni di fibre reticolari, linfociti e macrofagi.
La linfa viene filtrata all'interno di questi seni. I macrofagi eliminano le sostanze estranee attraverso la fagocitosi, mentre i linfociti distruggono gli agenti patogeni utilizzando le risposte immunitarie.
La linfa filtrata lascia il linfonodo attraverso la linfatica efferente ed emerge dall'altra estremità del nodo all'ilo.
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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.