The lymphatic system consists of a network of vessels lined with endothelial cells and interconnected lymph nodes, distributed throughout most of the body. It functions as a tissue drainage system, controlling the volume of blood and extracellular fluid and preventing tissue oedema. The lymphatic system collects tissue fluids and cells from most organs and tissues, transports it as lymph via a combination of intrinsic and extrinsic lymphatic pumps, ultimately returning these cells to blood. Dendritic cells patrol the tissues detecting danger signals and bringing foreign antigens back to the lymph nodes via afferent lymphatics where adaptive immune responses are induced. Thus, the lymphatic system integrates the immune system and widely dispersed organs and tissues, allowing for their protection from infections. It also plays a role in the turnover of macromolecules, which make up the extracellular matrix, fat absorption from the gut and immune function.
Key Concepts
The lymphatic system comprises a network of vessels lined by endothelial cells.
Lymphatic vessels drain nearly all tissues and organs in the body and interconnect lymph nodes.
Afferent lymphatics transport lymph from the tissues to lymph nodes, whereas efferent lymphatics transport lymph away from lymph nodes.
Lymphatics are essential for returning proteins, fluids and cells to blood, absorbing fat from the gut and are involved in the homeostasis of interstitial macromolecules.
The lymphatic system is a key regulator of extracellular fluid volume and is involved in preventing oedema.
The lymphatics play a central role in integrating the immune system, carrying lymphocytes, professional antigen‐presenting cells and antigens from the tissues to the lymph nodes.
Lymphatic endothelial cells function as professional antigen‐presenting cells, communicate directly with lymphocytes and antigen‐presenting cells to control cell traffic.