Lymph nodes [nodi lymphatici (PNA), lymphonodi (PNA, JNA), lymphoglandulae (BNA)] are pinkish-gray soft formations of round shape, with a diameter of 1 to 20 mm, located along the lymphatic vessels. Lymphatic vessels (see) of the body before flowing into one of the main lymphatic ducts are usually interrupted at least in one lymph node. However, some lymphatic vessels of the liver, thyroid, esophagus and other organs can directly flow into the large lymphatic ducts without interrupting the nodes. A person has 460 lymph nodes. In the human embryo, the lymph nodes appear after the basic lymphatic vessels are formed. The earliest lymph nodes develop in the area of the jugular and ilio-inguinal lymphatic sacs, in areas where the latter are replaced by a connective tissue.
The lymph node (Figures 1 and 2) has, on the one hand, an indentation - a hilus. In this place it includes arteries and nerves, as well as veins and vascular efferentia (vasa efferentia). The lymphatic vessels (vasa afferentia) bring the lymph node from its convex side. The lymph node is covered with a dense connective tissue capsule, rich in collagen fibers and containing a number of elastic fibers and smooth muscle cells. Inside the capsule, thin trabeculae move radially. On the incision of the lymph node, a darker cortex (cortex) and a lighter medulla are clearly visible.The
Fig. 1. Structure of the lymph node: 1 - bringing lymphatic vessels; 2 - capsule; 3 - trabeculae; 4 - enduring lymphatic vessels; 5 - the final sine; 6 - meat cords; 7 - intermediate sinuses; 8 - secondary nodules; 9 - edge sine.
Fig. 2. General view of the human lymph node (according to Bargmann).
Reticular tissue together with trabeculae constitutes the stroma of the lymph node. The cortical substance consists of folliculi (folliculi lymphatici), most of which are distinguished by the presence of light central areas surrounded by a peripheral zone with a high content of lymphoid cells. These lymphoid nodules are called secondary, unlike primary lymph nodes, devoid of such centers. Light central areas are the sites of lymphocyte neoplasms (see) and are called breeding centers. From the follicles inside the node stretch, called the pulp cords, consist of the same cellular elements as the follicles. Between the capsule and the trabeculae on one side, the follicles and the flesh cords on the other are spaces called sinuses. There are marginal sine between capsule and follicles; intermediate sinuses between follicles, fleshy cords and trabeculae and the terminal, or central, sine in the area of the node gate. Flesh cords, trabeculae and intermediate sinuses constitute the medulla of the node.
Blood supply of the lymph node is carried out by the arteries that enter it through the gate. They, branching, pass along the trabeculae, penetrating into the flesh cords and forming capillary nets around the follicles. The veins accompany the arteries or follow on their own, leaving the gate area.
The nerves of the lymph node follow along the course of the blood vessels and end with bush-shaped endings. In the lymph node also revealed polyvalent nerve endings, ending on the vessels and lymphoid tissue.
In childhood, the number of lymph nodes is greater, they lie closer to each other and are relatively larger. With age, the capsule of the lymph node thickens, the ratios of cerebral and cortical substances change, the size of sinuses. A part of the lymph node can be replaced by a connective and fatty tissue.The
The functional significance of the lymph nodes is determined by their participation in the processes of hematopoiesis (see) and the protective reactions of the organism (the latter is confirmed by such demonstrative experiment: in animals which from the moment of birth were brought up under sterile conditions, the lymph nodes hardly develop). Flowing through the lymph nodes, lymph (see) is enriched with lymphocytes that enter it from follicles and flesh cords. Lymph nodes are an active biological and mechanical filter. This property of the lymph nodes is due to the phagocytic activity of their reticuloendothelial elements. Mechanical filtration is carried out due to the peculiar architecture of the ways in which lymph passes through the node. Plasma cells in the lymph nodes produce antibodies.
Lymph nodes are located in the places where they are exposed to the muscles, come into contact with pulsating arterial trunks, etc. This gives grounds for assuming the involvement of lymph nodes in the progress of lymph by sucking and pushing it. Due to their considerable extensibility, the lymph nodes can regulate the amount of lymph flowing from the organ or area of the body. Particularly important is the involvement of lymph nodes in the regulation of lymphatic drainage of the thoracic and abdominal cavities. Lymph nodes are collectors of lymph from separate organs of the given area. The same lymph node can receive lymph from several organs and, conversely, several lymphatic vessels leading to different lymph nodes can leave the body. Groups of lymph nodes usually lie in permanent places, receive lymph from certain areas or organs and are called regional lymph nodes.
In some animals and in humans in the thoracic and abdominal cavities there are small, dark red nodes called hemolymphatic nodes. Outside, they are covered with a capsule, from which the trabeculae enter. Trabeculae in the node from the side of the capsule include arteries, accompanied by veins. The basis of the nodes is the reticular tissue, the follicles are located without special orientation, the sinuses are filled with blood. The origin and function of hemolymphatic nodes remain insufficiently elucidated.
Radioisotope studies of lymph nodes - see Lymphatic vessels. X-ray examination of lymph nodes - see Lymphography.