Lymph is the fluid circulating in the lymphatic system, and edema refers to fluid buildup in the body’s tissues; therefore, lymphedema is a buildup of lymph somewhere in the body’s tissues.Typically, this happens as a result of some obstruction in the lymphatic system.
All right, let’s back up and briefly talk about this lymph stuff. Oxygenated blood gets sent from the heart to your tissues via arteries, which get smaller and smaller until they feed the capillary beds. The capillary beds then provide nutrients to your cells and pick up waste. Now, deoxygenated blood then feeds back into larger and larger veins, and goes back to the heart. Pressure on the arterial side is a lot higher than on the venous side, so as blood comes into the capillary bed from the smaller arteries, called arterioles, the plasma — the colorless, fluid part of blood — is literally forced out into the interstitial space, or the space between cells. The majority of that fluid is reabsorbed on the venous side, but typically there’s more forced into the tissue through the arterial side than is taken out by the venous side.
Here’s where the lymphatic system comes into play. All of that excess fluid gets pulled into the afferent lymphatic capillaries, which are closed-ended vessels found throughout the body, including, scientists discovered in 2015, in the brain. These lymphatic capillaries have larger openings than the venous capillaries, which means that in addition to the interstitial fluid, they can accept larger proteins, cellular debris, and even bacteria, which get squeezed out of the arterial side, but are too large to get back into the venous capillaries. Once all of that stuff is in the lymphatic system, it’s called lymph. Also, those afferent lymphatic vessels have one-way valves that, along with smooth muscle contraction, keep the lymph moving along toward the lymph nodes, which have immune cells that once again help filter the fluid, getting rid of potential microbial threats. The fluid then leaves the lymph nodes and drains back into the systemic veins via the thoracic duct, or left thoracic duct, which empties into the left subclavian and jugular veins, and right thoracic duct, which empties into the right subclavian and internal jugular veins, to rejoin the blood once again.