The lymph system’s primary function is to isolate infection and cellular detritus from the rest of the body and deal with it. Imagine you are looking at a handful of living cells through a microscope. A capillary (the smallest blood vessel) delivers blood with its oxygen and nutrients. The local cells use these nutrients and excrete waste. There may be pathogens or antigens present that create an immune response, leaving dead cells and perhaps live infection. Some of the blood and waste products are picked up by tiny veins. But much of the vascular fluid and waste — and hopefully all of the live infection — is picked up by tiny lymph vessels. This process is happening all over the body all the time.
Like tributaries trickling into a stream that feeds a slow-moving river, the lymph system transports lymph fluid through ever-widening vessels, moving it through 500 filtration and collection points — your lymph nodes. At each successive node the lymph fluid is filtered and bacteria is removed. If lymph fluid is blocked in one lymph node it will usually take a detour, but when blockage is extreme it can cause the lymph fluid to back up and cause swelling in the surrounding tissue, a condition known as lymphedema.
The far-reaching lymph vessels merge at certain points to form lymphatic trunks. You have six major lymph trunks in your body, each responsible for draining filtered fluid from one region of the body.
The lumbar and intestinal trunks drain a large volume of purified lymph fluid upward from your lower extremities, pelvis and abdomen into the cisterna chyli, a widened collection pouch at the base of the thoracic duct.