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

Special Part
Lymphatic System (systema lymphaticum [systema lymphoideum]) - General Overview
Lymphatic vessels and regional nodes of specific body regions and organs - Development of the lymphatic system

Phylogenesis of The Lymphatic system

Comparative anatomical studies indicate that The Development of Lymphatic vessels occurs independently of one another. At later stages of animal phylogenetic development, the Lymphatic vessels and lymphatic tissue topographically and functionally unite into a single lymphatic system.

Lower vertebrates possess an undifferentiated hemolymphatic system. In teleost Fishes, the lymphatic system separates from the Circulatory system for the first time, forming two systems of lymphatic vessels: visceral (associated with the gastrointestinal tract) and parietal (of the body wall). The latter are formed from lymphatic vessels and expansions known as sinuses. The lymphatic sinuses communicate with the lymphatic vessels. In fishes, amphibians, and reptiles, lymphatic vessels lack Valves.

The lymphatic vessels of amphibians and reptiles are characterized by the presence of Lymph hearts (contractile Organs) that facilitate lymph flow into the Venous system. The lymphatic system of amphibians and reptiles contains from 2 to 25 lymph hearts. Lymph Circulation through the lymphatic vessels in reptiles is ensured primarily by the contraction of body Muscles. In fishes, amphibians, and reptiles, lymphoid tissue is not organized into lymph (lymphoid) nodes, but is represented by isolated islands that are not connected to lymphatic sinuses and vessels.

In birds, lymph hearts are present only during the Embryonic Stage of development. The lymphatic vessels of mammals contain valves that promote the unidirectional flow of lymph. This circumstance led to the reduction of lymph hearts. The lymphatic vessels of birds empty into the cranial and brachiocephalic Veins. Lymph Nodes are found in some families of birds.

In mammals, the lymphatic system is complex, resembling The Structure of the human lymphatic system. A large number of lymph nodes appear, and the lymphatic vessels feature valves that facilitate the unidirectional flow of lymph. Lymph drains into the lymphatic vessels through a chain of LYMPH NODES AND then flows via large trunks into the venous angles, where venous pressure is low.

Class="center">Embryonic Development of the Lymphatic System

In humans, lymphatic vessels develop from the mesenchyme, separately from the circulatory system near the developing large veins. Initially, cleft-like spaces appear, bounded by mesenchymal Cells, which subsequently condense and transform into endothelial cells. These cleft-like spaces interconnect to form a system of channels that fuse and proliferate, thereby forming lymphatic sacs. By the 6th week of intrauterine development, the right and left jugular sacs are formed.

Somewhat later, the so-called subclavian lymphatic sacs develop in the subclavian regions. The chain of lymphatic sacs located along the left dorsolateral body wall gives rise to the main lymphatic trunk—the Thoracic duct, which at its initial stage of development (9th week) opens into the jugular lymphatic sac. From the retroperitoneal (mesenteric) sacs in the lumbar region, an expansion of the initial part of the thoracic duct is formed—the cisterna chyli (thoracic duct cistern, cisterna ductus thoracici). Slightly more caudally, lymphatic vessels sprout from the retroperitoneal sac, ensuring lymph drainage from the Organs of the gastrointestinal tract and Kidneys. Paired iliac lymphatic sacs at the level of the Abdominal Aorta bifurcation continue into iliolumbar and ilioinguinal expansions. The latter form the lymphatic vessel System of the lower extremities, as well as of the rectum and Perineum.

By the 9th week of intrauterine life, the main lymphatic vessels assume their characteristic position. Valves appear near the junction of the subclavian lymphatic sacs with the brachiocephalic veins (at the Mouth of the thoracic duct and the left jugular trunk). The connection of the jugular lymphatic sac with the neck lymphatic vessels forms the jugular lymphatic trunk. In the caudal section, the thoracic duct forms the cisterna chyli, which in turn communicates with the mesenteric and ilioinguinal trunks (vessels). Subsequently, lymphatic vessels are formed from the lymphatic sacs through the sprouting of endothelial outgrowths and their canalization. In the process, the lymphatic sacs narrow and transform into lymphatic collectors.

Lymph nodes begin to develop along the course of lymphatic vessels starting from the 3rd month of intrauterine life. In specific locations near the lymphatic vessels, clusters of mesenchymal cells appear; the outer layer of the lymphatic vessel wall participates in forming the node capsule, while the vessel lumen transforms into the marginal (subcapsular) sinus. The intermediate and hilar sinuses of the lymph node form later. The parenchyma of the lymph node subsequently develops from the central Regions of the mesenchymal lymph node primordium. The formation of follicles within the lymph node parenchyma is observed by the beginning of the 5th month of intrauterine life, in conjunction with the development of the lymph node Blood Vessels. Before birth or immediately thereafter, the Differentiation of the cortical and medullary substances of the nodes occurs. All Structural components of lymph nodes also exhibit age-related characteristics during Postnatal ontogenesis.

Anomalies in the Development of the Lymphatic System

The most common Anomalies of the lymphatic system include: aplasia of efferent lymphatic vessels, leading to organ elephantiasis; and hypoplasia, characterized by a marked reduction in the lymphatic system.

Congenital cysts are large dilations of the walls of efferent lymphatic vessels.

Lymphangiectasia refers to congenital dilations of the lymphatic capillaries, vessels, and thoracic duct.

Lymphangiomas are tumors of the lymphatic vessels.

Impaired lymph drainage is a condition in which the lymphatic system fails to provide its drainage function.

Lymphangitis is inflammation of the lymphatic vessels accompanied by deformation of their walls, leading to lymphostasis and elephantiasis. Lymph nodes feature a complex pathway of sinuses and can pool a significant amount of lymph during stasis.

Under pathological conditions, lymph nodes increase in size and change their external shape, as noted by F. Ya. Prymak (1938), D. D. Zerbino (1966), and others. For diagnostic purposes, morphological analysis of lymph nodes is performed using cytological and histological Methods.

The architectonics and histotopography of the lymphatic system plexuses within organs are determined by the STRUCTURE OF THE latter and their Connective Tissue framework. Lymph nodes produce a leukocyte factor that stimulates Cell proliferation.