Human Anatomy, Part 2 - K. A. Dyubenko, A. K. Kolomiysev, Yu. B. Chaykovsky 2008

Special Part
Lymphatic system (systema lymphaticum [systema lymphoideum]) — General overview

Along with the Circulatory system, The Human Body features The Lymphatic system, systema lymphaticum (PNA, BNA); [systema lymphoideum] (Fig. 99). This is a subdivision of The Vascular System that integrates the pathways of Lymph transport: lymphatic capillaries, lymph node sinuses, Lymphatic vessels, lymphatic trunks, and lymphatic ducts, as well as lymph hearts in animals (V. V. Kupriyanov et al., 1983). The lymphatic system (via the endothelium of lymphatic capillaries) carries out the resorption of intercellular fluid, resulting in The formation of lymph. Lymph then passes through lymphatic vessels, Lymph Nodes, trunks, and ducts, finally entering the Venous system; thus, it constitutes an integral part of the vascular system. Working in concert with the venous system, the lymphatic system performs tissue drainage and, together with immune Organs, fulfills A number of specific Functions: barrier, lymphopoietic, immune, and others.

In addition, the lymphatic capillaries absorb fluid from serous cavities (abdominal, pleural, pericardial) as well as synovial fluid from joint cavities. The initial segments of the lymphatic system can take up colloidal solutions of macrodisperse Proteins, particulate Suspensions from cavities, foreign particles including Bacteria, and malignant tumor Cells.

Lymph (Lat. lympha, clear Water, pure spring; Greek lymphe, a modification of nymphe, goddess of the fields) is a fluid tissue of the body found within Lymphatic vessels and nodes. Lymph is yellowish in color, salty to the taste, transparent, and resembles Blood Plasma in its cellular component composition. Occasionally, lymph has a light pink hue due to the presence of erythrocytes, or an opalescent appearance caused by fat particles.

Lymph is formed from "tissue fluid" that passes through a living Cell/33.html">Plasma Membrane—the endothelium of lymphatic capillaries—and then enters lymphatic vessels, lymph nodes, trunks, and ducts. It contains colloidal protein solutions, crystalloids, and cellular elements (lymphocytes). Unlike blood, which circulates in a closed loop, lymph flows in a single direction, from the periphery to the center; as S. K. Drinker put it, "lymph flows from blood to blood." Lymph participates in the body's immune responses by transporting plasma cells, macrophages, immune lymphocytes, Antibodies, and other substances from lymphoid organs.

According to some researchers (I. Rusznyák, M. Földi, D. Szabó, 1957), the human lymphatic vessels and lymph node sinuses contain between 1 and 2 liters of lymph.

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Fig. 99. General diagram of the human lymphatic system (after D. A. Zhdanov)

Fig. 100. Nerve endings on a lymphatic capillary. Injection of lymphatic vessels with silver nitrate, nerve elements by Bielschowsky-Gross. Objective approx. 90, eyepiece approx. 7 min. Preparation by K. S. Kabak and A. K. Kolomiytseva

Unlike the circulatory system, the human lymphatic system lacks a dedicated pump like The Heart to facilitate the movement of lymph through the vascular network. Continuous lymph drainage through the lymphatic vessels is driven by several factors: blood vessel pulsation, the terminal pressure of lymph in lymphatic capillaries, contraction of lymphangion walls in lymphatic vessels, contractions of striated and smooth Muscles of Internal Organs, the suction action of the thoracic cavity, heart and Diaphragm contractions, and active limb movements. Furthermore, continuous lymph outflow from organs depends on the functional state of the blood microcirculatory bed, as well as the Structure and function of the lymphatic capillary endothelium.

Fig. 101 A, B. Structural diagram of: A - a lymphatic capillary; B - a lymphatic vessel

The activity of the lymphatic system is regulated by The Nervous system. Under its influence, lymphatic vessels can alter their lumen or close entirely, becoming temporarily excluded from lymph Circulation. Nerve fibers accompany lymphatic capillaries over varying distances, cross them, or sometimes encircle the capillary in ring-like formations. In certain organs, Neurons or ganglia are found along the course of lymphatic vessels and capillaries. In addition to nerve fibers and neurons, numerous nerve endings are associated with lymphatic capillaries in the form of loops, buttons, nets, tufts, as well as non-encapsulated and encapsulated corpuscles (Fig. 100). Thus, the initial segments of the lymphatic system possess specialized innervation to regulate tissue fluid absorption, lymph flow, and Changes in the lumen of vessels and capillaries.

Functions of the Lymphatic System

The primary function of the lymphatic system is the formation and conduction of lymph from Tissues and organs into the venous system. Concurrently, the lymphatic system performs tissue fluid absorption (the drainage function), which is sometimes compared to groundwater. It maintains a constant volume and composition of interstitial fluid, thereby participating in internal environment Homeostasis. The lymphatic system establishes a humoral connection between intercellular fluid, lymphoid structures, and blood, while also resorbing water, colloidal solutions, proteins, water-soluble crystalloids, and cell breakdown products from tissues that are not absorbed by blood capillaries. It facilitates the absorption and transport of various Digestion breakdown products from the intestine into the venous system, as well as fluid from serous cavities. Lymph nodes are located along the course of lymphatic vessels. They perform a barrier function by trapping foreign particles and malignant tumor cells, as well as neutralizing microbes that invade the body. Lymph nodes carry out a lymphopoietic function (lymphopoiesis) by producing lymphocytes that enter the lymphatic and blood streams. The human body contains approximately three trillion lymphocytes. Additionally, lymph nodes participate in immune responses because they produce plasma cells that synthesize antibodies, and they house T AND B lymphocytes responsible for humoral and cellular Immunity.