Lymph Fluid

Lymph fluid is the clear interstitial fluid that is found between the cells of the human body. This fluid enters the lymph vessels by the method of filtration through the pores that are present in the walls of capillaries. The secreted lymph then travels to any one or more of the lymph nodes before emptying eventually into the right or the left subclavian vein where it mixes back with the blood. Given below are details on fluid formation, composition, circulation and the diseases affecting the lymphatic system.

Lymph Formation
Blood supplies nutrients and important metabolites that are required by cells and then collects back all the waste products that are produced as a result of all the metabolic activities. This collection of waste products requires exchange of respective constituents between the cells and blood. This exchange is not done directly but is carried out by the interstitial fluid present between the cells. Due to continuous exchange of substances between the cells and the interstitial fluid, its composition continuously changes. Water and solutes can freely diffuse through the capillaries.

As interstitial fluid forms at the arterial end of the capillaries, that is, from the side where blood is coming from the heart, due to the higher blood pressure that it flows under when compared to veins, most of it returns to the venous ends. However, the rest enters the lymph capillaries as lymph. Hence, when lymph is formed, it is a watery clear liquid which has the same composition as that of interstitial fluid. However, as it passes through the lymph nodes, it comes in contact with blood and tends to accumulate cells like lymphocytes and proteins.

Lymph Composition
Lymph has a composition that is quite similar to that of blood plasma. However, it may differ slightly based on the type of tissue that it is draining. Lymph contains cells like white blood cells. The concentration of lymphocytes, a type of white blood cell, is higher in the lymph fluid when it leaves a lymph node.

Lymph Circulation
There are certain tubular vessels that are responsible for transporting lymph back into the blood stream, thus, ultimately replacing the volume of blood lost during interstitial fluid formation. These channels through which lymph flows are known as lymphatic channels. Since there is no central pump in the lymphatic system, unlike the cardiovascular system, lymph still travels from one center to another. This occurs even under low pressure due to the propulsion of lymph through the lymphatic channels by contraction and relaxation of the smooth muscles, valves and due to adjacent arterial pulsation.

Lymph Disorders
There are many lymphatic system diseases that can eventually affect the composition or flow of lymph. These diseases normally affect the lymph nodes. These include:

• Lymphedema is the condition where there is obstruction of the lymphatic system. In this condition, there is fluid build up which leads to edema and swelling. This may occur due to either obstruction due to an overgrowth or due to an infections, like filariasis. The lymph fluid retention may lead to other problems as well. Sometimes, there may be lymph leakage after a surgical procedure.
• Lymphadenopathy is an increase in the size of the lymph nodes. This normally signifies the presence of an infection or disease in the body.
• Lymphadenitis is a condition where there is inflammation of the lymph node and the lymphatic system.
• Lymphoma is a type of cancer that arises from the lymph nodes. In this condition, the lymphocytes undergo changes and start to multiply uncontrollably.

Lymphatic system is an important part of the body's defense system which helps to fight off infections, most of which is carried out by this clear fluid.