The lymphatic system is the group of organs that ensure the circulation of lymph. This system includes a network of vessels, organs and lymphatic nodes.
The lymphatic system transports lymph through a network of vessels, organs and lymphatic nodes. It also plays a crucial role in the body’s defence, as antibodies and certain white blood cells circulate through this system. Other molecules, such as lipids, can also circulate in these vessels.
The human body contains different fluids that have different names depending on where they’re found.
The blood, circulating in the blood vessels, contains plasma. As blood passes through a capillary bed, some of the plasma escapes and fills the space between the capillaries and the surrounding cells. It is now called extracellular fluid or interstitial fluid. It is responsible for the exchanges between the bloodstream and the cells. There are also lymphatic vessels in the capillary bed. They collect the interstitial fluid. Once inside the lymphatic vessels, it is called lymph. It is composed mainly of water but also contains white blood cells.
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Lymph Circulation (Advanced Concepts)
The lymphatic system is divided into two parts: a network of lymphatic vessels and the lymphatic nodes and organs.
Just like blood vessels, lymphatic vessels transport lymph throughout the body. This means that after leaving the bloodstream through the blood capillaries, the lymph can return to the bloodstream through two subclavian veins (near the clavicle). The lymph circulating in the upper right part of the body passes through the right subclavian vein, and the rest passes through the left subclavian vein.
The lymph circulates through the body as the muscles compress the lymphatic vessels. There is no "pump" in the lymphatic system.
Lymphatic nodes are small bumps that produce white blood cells, among other things. These nodes are spread throughout the body, as shown in the following image.
When a person is sick with the flu their lymphatic nodes swell, which can be easily felt to touch. Often, the nodes closest to the infection will be the first to swell (the flu makes the nodes in the neck react first). Lymphatic nodes usually swell because these white blood cells inside them actively divide to increase their numbers and the immune response to infection.
The lymphatic system also includes lymphatic organs, such as the thymus, bone marrow, spleen and tonsils. All lymphatic organs, as well as lymphatic nodes, contain numerous white blood cells and filter the lymph to remove any cell debris, bacteria or viruses.