General characteristics and composition of lymph
The morphological basis of the system is an extensive set of lymphatic vessels and lymph nodes. Lymph circulates within this bed—a biological fluid whose total volume in an adult human reaches approximately 3 liters.
In its basic chemical composition, lymph is extremely similar to blood plasma. However, there is a fundamental difference between them: lymph contains significantly less protein. At the same time, the walls of lymphatic capillaries and vessels have exceptionally high permeability. Unlike blood capillaries, they are capable of freely letting large protein molecules, as well as other large particles trapped in the intercellular space, into the lumen.
Topographical features
The lymphatic network permeates the vast majority of tissues and organs of the human body, providing full drainage. Nevertheless, there are specific anatomical zones where lymphatic vessels are completely absent. Such structures include:
- The central nervous system (CNS) and meninges.
- Cartilage tissue (due to the specifics of its nutrition).
- Structures of the visual apparatus: the cornea and the eyeball.
Main functions of the lymphatic system
The physiological role of this vascular bed section is multifaceted. Four key functions are distinguished:
- Drainage function: the system continuously removes accumulated metabolic products and excess free water from the interstitium (intercellular space), thereby preventing the development of tissue edema.
- Transport function: the transport of hydrolysis products occurs through the lymphatic pathways. First and foremost, this concerns lipids, which are absorbed from the digestive system. In addition, the system ensures the vital return of proteins and electrolytes from tissues back into the bloodstream.
- Protective function: lymphatic vessels actively participate in the transport of foreign antigens. The formation of both primary and secondary immune responses takes place in the nodes and other structures.
- Hematopoietic function: the process of lymphopoiesis—the formation and maturation of new lymphocytes—continues directly within lymphoid tissue.
Lymphodynamics: mechanisms of lymph movement
Lymph hemodynamics, or lymphodynamics, describes the processes that ensure the continuous movement of fluid from peripheral tissues to the venous bed. This movement occurs against gravity and is supported by a number of factors:
- Contractile activity: rhythmic contractions of the walls of the lymphatic vessels themselves push the fluid forward.
- The suction action of the chest: negative pressure arising in the thoracic cavity during inspiration creates physical traction that helps propel lymph upward.
- Presence of valves: a developed valve apparatus is located inside the vessels, which reliably prevents the backflow of fluid.
Regulation of movement occurs at the microscopic level through the contraction of myocytes of lymphangions (structural and functional units of the vessel). Control over this contractile activity is under the pronounced influence of the sympathetic nervous system, which is capable of altering the tone and motility of the lymphatic bed.
Briefly: answers to topical questions
What are the mechanisms of tissue fluid formation, from which lymph is subsequently formed?
The mechanisms of tissue fluid formation are based on the difference between hydrostatic and oncotic pressures in blood capillaries. At the arterial end of the capillary, hydrostatic pressure predominates over oncotic pressure, resulting in fluid exiting the vessel into the tissue. At the venous end of the capillary, hydrostatic pressure drops to 20 mm Hg, while the oncotic pressure of the plasma (30 mm Hg) drives the osmosis of water back into the blood. The fluid remaining in the tissues accumulates, stretching the anchoring filaments of the lymphatic capillaries. They push the endothelial cells apart, forming a cleft between them through which tissue fluid enters the lumen of the lymph capillary.
Through which large lymphatic ducts is lymph returned to the venous bed?
The return of lymph to the venous bed is carried out through large lymphatic ducts:
- Thoracic duct (ductus thoracicus) — the main lymphatic vessel that collects lymph from most of the body: the lower extremities, pelvis, abdominal cavity, left half of the chest, left arm, and left half of the head and neck.
- Right lymphatic duct (ductus lymphaticus dexter) — formed by the convergence of the right jugular, subclavian, and bronchomediastinal trunks; it empties into the right venous angle or subclavian vein.
Venous angle — the junction of the internal jugular vein with the subclavian vein.
Class and exam questions
What is the main difference in the composition of lymph versus blood plasma?
Lymph is very similar in composition to plasma, but contains a significantly lower amount of protein.
Why does lymph not flow in the reverse direction under the action of gravity?
The backflow of lymph is prevented by the presence of special valves in the lymphatic vessels.
What part of the nervous system controls lymphodynamics?
The regulation of lymph movement and contraction of lymphangion myocytes is under the control of the sympathetic nervous system.
In which organs and tissues are there no lymphatic vessels?
They are absent in the CNS, meninges, cartilage tissue, as well as in the cornea and eyeball.
What else to study on this topic
- Structure and contraction cycle of the lymphangion
- Mechanisms of lipid absorption and transport in the digestive system
- The process of lymphopoiesis in lymphoid tissue
- Involvement of the lymphatic system in the formation of the immune response
- The role of the chest's suction action in hemo- and lymphodynamics
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