General Characteristics and Lymph Composition
The morphological basis of the system is an extensive network of lymphatic vessels and lymph nodes. Lymph circulates within this network—a biological fluid whose total volume in an adult reaches approximately 3 liters.
In its basic chemical composition, lymph is extremely similar to blood plasma. However, there is a fundamental difference: lymph contains significantly less protein. At the same time, the walls of lymphatic capillaries and vessels possess exceptionally high permeability. Unlike blood capillaries, they can freely let large protein molecules and other large particles from the intercellular space into their 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. These structures include:
- The central nervous system (CNS) and meninges.
- Cartilage tissue (due to its specific nutrition mechanism).
- Structures of the visual apparatus: the cornea and the eyeball.
Main Functions of the Lymphatic System
The physiological role of this vascular division is multifaceted. There are four key functions:
- Drainage function: the system continuously removes accumulated metabolic waste products, as well as excess free water, from the interstitium (intercellular space), thereby preventing tissue edema.
- Transport function: hydrolysis products are transported via lymphatic pathways. This primarily concerns lipids absorbed from the digestive system. Additionally, the system ensures the vital return of proteins and electrolytes from tissues back into the bloodstream.
- Protective function: lymphatic vessels actively participate in transporting foreign antigens. Both primary and secondary immune responses are formed within nodes and other lymphoid 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 ensuring the continuous movement of fluid from peripheral tissues to the venous bed. This movement occurs against gravity and is supported by several factors:
- Contractile activity: rhythmic contractions of the walls of the lymphatic vessels themselves propel the fluid forward.
- Thoracic pump effect: negative pressure generated in the thoracic cavity during inspiration creates physical traction that helps move lymph upward.
- Presence of valves: a well-developed valve system inside the vessels reliably prevents the backflow of fluid.
Movement regulation occurs at the microscopic level through the contraction of myocytes within lymphangions (the structural and functional units of the vessel). Control over this contractile activity is heavily influenced by the sympathetic nervous system, which can alter the tone and motility of the lymphatic bed.