Owing to intimacy and certain functional similarities, lymphatic system lymphatic system is rightly considered a part of the circulatory system. In this connection, it not only receives its circulatory fluid from the blood, but also returns the same back to the blood. However, its constituent organs are: capillaries, vessels, nodes, ducts and lymph. Similarly, it is assisted by some other organs as well, such as spleen, thymus, tonsils and appendix, which otherwise are considered as a part of the lymphoid system. Given below is a brief description of each of these lymphatic system organs:

Lymphatic Capillaries

Found in the intercellular spaces throughout your body, lymphatic capillaries are the tiny, thin-walled and blind-ended vessels. However, these are absent in the non-vascular tissues and in the CNS (Central Nervous System). When some of the blood plasma, instead of returning back to the circulatory system, gets accumulated around the body cells in the form of interstitial fluid, it needs to be removed or drained by some other means. This is the time for lymph capillaries to play their role by collecting this left-over liquid and delivering it back to the blood stream. If you compare lymphatic capillaries with those of the blood capillaries, the former have a bit larger diameter than that of the latter. Owing to the unique structure of the lymph capillaries, the interstitial fluid can only penetrate into the interior, but cannot escape out.

Lymphatic Vessels

The thin walled, valved structures in the body that transport lymph from one place to another are called lymphatic vessels. They account for an important part of the lymphatic system, and play a complementary role in the proper functioning of cardiovascular system. When blood plasma, cells and other substances get leaked out of the body’s vascular system, these vessels collect all such things in the form of lymph and deliver them back to the circulatory system. However, the lymph is actually collected by the smaller tubes, called lymphatic capillaries, which is then received by these larger channels.

Lymph Nodes

These oval-shaped structures are also known as lymph glands and are scattered widely throughout your body. They not only serve as an integral part of the lymphatic system but play an important role in the immune system of your body. Their indispensable functionality in the immunity of the body can be realized from the simple fact that they serve as garrisons of the B, T and other immune cells. Tightly packed with WBCs (White Blood Cells), including lymphocytes and macrophages, these nodes just act as check posts or filters where harmful foreign substances are trapped and destroyed.

Lymphatic Ducts

The great lymphatic vessels in the body are called lymphatic ducts which are two in number, namely, the thoracic duct and the right lymphatic duct. The lymphatic fluid collected in these ducts is emptied into the subclavian veins.

The Right Lymphatic Duct

Measuring about 1.25 cm in length, the right lymphatic duct was discovered by Neils Stensen (the birth name of Nicolas Steno). Coursing along the median border of the Scalenus Anterior at the root of your neck, it forms various combinations with the right internal jugular vein and the right subclavian vein. Its major function is to drain lymph from the upper right section of the trunk; the right side of the head and neck; and the right arm.

The Thoracic Duct

The thoracic duct, on the other hand, is comparatively longer and may attain the length of up to 45 cm in human adults, whereas its average diameter is about 5 mm. Originating from the confluence of the intestinal trunk and the left and right lumbar trunks in the abdominal region, it extends upward to the root of the neck. In adult humans, the thoracic duct has been found to transport about 4 liter of lymph on daily basis.

Lymph

The most important part of this accessory lymphatic system is lymph, which is a clear liquid and flows through the capillaries, vessels and ducts. However, before being emptied into the left or the right subclavian vein, it is transported to the lymph glands or nodes which serve as check posts for trapping and filtering foreign substances. Concerning its formation, this tissue fluid is formed when the interstitial fluid is collected with the help of blind-ended lymphatic capillaries. So far as the ingredients of lymph are concerned, you can compare its composition to that of the blood plasma, but a slight difference can be noticed. For example, the tissue fluid or lymph also contains white blood cells which are not found in the blood plasma. In another instance, the fluid formed in your digestive system (called chyle) looks milky white and is rich in triglycerides.

Spleen

Located just behind the stomach and to the left side of the body, in the abdominal cavity, spleen is a secondary lymphoid organ. Its normal color can be either red or purple and its entire sac-like structure is enclosed by a collagenous capsule. A part of the support structure of this organ is formed by the collagenous extensions, called trabeculae. Resembling a large lymph node in structure, the primary function of the spleen is to act as blood filter.

Thymus Gland

This secretary organ is present between the heart and sternum, and plays an important immunological role in your body. Regarding structure, you can divide it into two identical lobes, central medulla and outer cortex. Thymus carries out the production and secretion of the thymosins which control the development and functioning of the important cells of Adaptive Immune System, called T-Lymphocytes.