Good morning everyone, we all know that in our body the blood never leaves the blood vessels. Then how do the nutrients etc get passed to the cells and how do excretory products reach blood from the cells? This means something must be there in between blood and tissues. If you sit with your legs crossed for a long time, say you were studying or watching a movie, then you don't feel your leg as if blood is not flowing through it and it is filled with water. Actually, it is because of too much tissue fluid. So how does it happen? Also, if too much tissue fluid stayed there, the legs would swell a lot. But this doesn't happen normally. So how is this situation controlled and brought back to normal? You know, some liquid or plasma part of blood comes out of the blood capillaries because of the blood pressure and flows into the tissues. That is between the spaces between the individual cells. We call it tissue fluid. It is this tissue fluid that delivers nutrients, oxygen and other chemicals to the cells. Then the tissue fluid leaves the cell and removes waste products. So we see actually it is not the blood that directly comes in the contact with the tissues or cell for the transport of substances. It is actually done by the tissue fluid. Now after this task is complete, most of the tissue fluid returns to the circulatory system as venous blood by entering venuals which later form veins. In case you don't remember, venuals are a type of blood vessel that connects capillaries to veins. Now what happens to the remaining tissue fluid? The rest of the tissue fluid needs to get back to the bloodstream too. How? A separate system accomplishes this task and it is called lymphatic system. The lymph is the fluid that circulates throughout the lymphatic system. The lymph is formed when the tissue fluid is collected through lymph capillaries. So remember only the tissue fluid that enters the lymphatic system is actually lymph and is similar to plasma of the blood. But it is colorless and has less proteins. From the lymph capillaries, the lymph is then transported through larger lymphatic vessels to the lymph nodes. In the lymph nodes, it is cleaned by lymphocytes which are specialized white blood cells. The lymph is ultimately emptied into the right or the left subclavian vein where it mixes back with the blood. So we see the lymph is the vital link between the tissue and the blood. When a skeleton muscle contracts, it applies pressure on the lymphatic vessel causing the lymph to flow. Some of what we learned today, the primary function of the lymphatic system is to transport lymph throughout the body. The major functions carried out by lymph while the lymphatic system are, it drains excess fluid from extracellular space back into blood. It carries digested and absorbed fat from intestine. You know it is the lymphatic capillaries called lacteels that absorb fat in the willy or willy of small intestine. Lastly, the lymph contains lymphocytes which are responsible for the immune responses of the body. That's all for now. Bye bye.