Human Anatomy Part 2 - K. A. Diubenko, A. K. Kolomiitsev, Yu. B. Chaikovsky 2008

Special Part
Organs of the Hematopoietic and Immune Systems - General Information
Secondary Lymphoid Organs - Lymph Nodes

Lymph Nodes, nodi lymphatici (PNA), or nodi lymphoidei (BNA), belong to the Secondary Lymphoid Organs. They participate in lymphocytopoiesis, antibody production, and lymph storage. As lymph flows and filters through the lymph nodes, it becomes enriched with lymphocytes and Antibodies, and is cleared of microorganisms and foreign particles. A general description of regional lymph nodes is provided in the "Lymphatic system" section.

Structure of a lymph node (Fig. 118). Morphologically, lymph nodes are classified as bean-shaped, spherical, or ovoid. Externally, the lymph node is covered by a grayish Connective Tissue capsule, from which trabeculae (septa) of various sizes extend into the parenchyma. Inside the lymph node, between the trabeculae, lies the stroma, composed of reticular fibers and Cells that form a three-dimensional meshwork with meshes of various Sizes and Shapes (M. Sugimura et al., 1963). Slit-like spaces—lymphatic sinuses*, lined with endothelium—are located between the trabeculae and the lymphoid tissue. Lymph flows through the node via these sinuses. There is a subcapsular or marginal sinus, sinus intermedius corticalis, located between the capsule and the follicles. Afferent Lymphatic vessels open into it. Intermediate sinuses, sinus intermedius corticalis, transition into medullary sinuses (located between the medullary cords and trabeculae). The medullary sinuses lead into the hilar sinus, from which efferent lymphatic vessels emerge. Thus, the incoming lymph is filtered as it flows from the subcapsular sinus to the hilar sinus (A. Ham et al., 1983). The parenchyma of the node consists of the cortex, the medulla, and the paracortical zone. The cortex is located at the periphery of the node and consists of lymphatic nodules (follicles), noduli lymphatici, which are round or oval clusters of lymphoid tissue about 0.5–1 mm in diameter; the diameter of individual nodules can reach 1 to 3 mm. The central part of a follicle may contain a lighter zone—the germinal center.

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Fig. 118. Structure of a lymph node (diagram)

Blood supply. Lymph nodes have a rich blood supply from Blood Vessels that enter through the hilum and capsule, branching within the parenchyma into capillaries. These capillaries form superficial and deep fine-meshed capillary networks, which give rise to postcapillary venules that drain venous blood into venules. Lymph nodes are innervated by adjacent nerves. They are highly sensitive to both external and internal factors. Ionizing radiation rapidly destroys lymphocytes. Adrenal cortex insufficiency leads to the condition known as status thymicolymphaticus.

For diagnostic purposes, morphological analysis of lymph nodes is performed using cytological and histological techniques.

* In Latin, the term "sinus" means a hollow space, while the term "sinusoid" is derived from the Latin "sinus" and the Greek "eidos"—resembling. Thus, a sinusoid is something resembling a hollow space. In anatomy, the term "sinus" is used to designate a hollow space. In Histology, a sinus refers to a thin-walled vessel with a relatively large lumen through which blood or lymph flows. In lymph nodes, the marginal sinus is a hollow space rather than a tube, which is why it is called a sinus.

Hemolymph nodes

Hemolymph nodes, nodus lymphaticus haemalis, belong to the peripheral Hematopoietic organs. They are located in the periadrenal tissue, along the Abdominal Aorta and renal Arteries, and occasionally in the posterior Mediastinum. They are smaller in size than lymph nodes. Externally, they are covered by a connective tissue capsule. The parenchyma consists of a cortex and a medulla. Hemolymph nodes produce formed elements of blood of both lymphoid and myeloid lineages. With age, hemolymph nodes are replaced by adipose tissue.