Lymph

Lymph is the fluid that is formed as the interstitial fluid enters the lymph vessels by filtration. The lymph then travels to at least one lymph node before emptying ultimately into the right or the left subclavian vein, where it mixes back with blood.

Composition of lymph

Lymph has a composition comparable to that of plasma, but it is different in various parts of the body depending upon the tissue drained. In particular, the lymph that leaves a lymph node is richer in lymphocytes. Likewise, the lymph formed in the digestive system called chyle is rich in triglycerides (fat), and looks white.

Formation of lymph

Blood supplies nutrients, and important metabolites to the tissues, and collects back the waste products that they produce, which requires exchange of respective constituents between the blood and tissues. However, this exchange is not direct, and is effected through an intermediary called "interstitial fluid" or "tissue fluid" that the blood forms. Interstitial fluid (ISF) is the fluid that occupies the spaces between the cells and acts as their immediate environment. As the blood and the surrounding cells continually add and remove substances from the ISF, its composition keeps on changing. Water and solutes can freely pass (diffuse) between the ISF and blood, and thus both are in dynamic equilibrium with each other; exchange between the two fluids occurs across the walls of small blood vessels called capillaries.

ISF forms at the arterial (coming from the heart) end of the capillaries because of higher pressure of blood, and "most of it" returns to its venous ends and venules; the rest (10—20%) enters the lymph capillaries as lymph.]

Unlike the cardiovascular system, the lymphatic system is not closed and has no central pump. Lymph movement occurs despite low pressure due to peristalsis (propulsion of the lymph due to alternate contraction and relaxation of smooth muscle), valves, and compression during contraction of adjacent skeletal muscle and arterial pulsation.cite journal | author = Shayan, Ramin; Achen, Marc G.; Stacker, Steven A.
year = 2006 | title = Lymphatic vessels in cancer metastasis: bridging the gaps | volume = 27 | issue = 9 | pages = 1729 | doi = 10.1093/carcin/bgl031 | url = http://carcin.oxfordjournals.org/cgi/content/full/27/9/1729 | pmid = 16597644 | journal = Carcinogenesis ]

Usually, the lymph that enters the lymph vessels from the interstitial space, does not leak back because of presence of valves. But, in case of blockage of free flow, when excessive hydrostatic pressure develops within the lymph vessels, some fluid can leak back and contribute to formation of edema.

See also

* Lymphatic system
* Lymphedema

References