 Hello, my name is Alma, I have a bachelor of biomedical science and I'm going to take you through the basics of the lymphatic system. The lymphatic system serves four important functions. It maintains fluid levels in your body, protects your body against foreign invaders, it removes waste products and finally it absorbs fats from the digestive tract. In this video we're going to talk about the first three, because they're the ways the lymphatic system acts to support our whole body. As we have seen in the circulatory system, the exchange of nutrients and waste occurs at the capillary beds. Now, for the most part, the plasma that is pushed out is collected again through osmotic pressure, but about 3 liters per day out of 20 liters that are pushed out remain in the interstitial space. This is where the lymphatic system comes in. Those remaining three liters are picked up by lymphatic capillaries that are intertwined with the capillary bed. This fluid, now called lymph, flows up various lymphatic vessels to two big ducts which return the fluid back to the circulatory system. Since the lymphatic system does not have a heart to pump the fluid around, the upward flow occurs through the contraction of smooth muscles in the lymphatic vessels. Similarly to veins, lymphatic vessels also have valves to prevent backward flow. Returning the lymph back to the circulatory system is of vital importance. The fluid which is recovered maintains blood pressure, which allows for nutrients, such as oxygen, to be pushed out of the capillaries to sustain all of your cells. A small decrease in blood pressure can cause dizziness and fainting, and larger decrease can be life-threatening. So the lymphatic system is carrying out a very important job. But let's rewind a bit, because on the journey back to the circulatory system, lymph undergoes a few other important processes. The lymph collected at the capillary beds contains waste products, cell debris, and possibly pathogens. These nodules we can see here are lymph nodes. The function of the lymph nodes is to filter out the cell debris, as well as to store and produce some immune cells. So on the journey up to return the fluid to the circulatory system, lymph passes through lymph nodes, which through the immune cells it contains remove waste and destroy pathogens. If it's necessary, these immune cells can also kickstart a wider immune response. Often, this results in those lymph nodes swelling. You might have noticed this before when you've been sick. For example, with a cold, the lymph nodes on your neck might swell up. But this is not all the lymphatic system does for the immune system. As well as lymph nodes, the lymphatic system includes a few other lymphoid tissues. These are the bone marrow, the thymus, the spleen, the adenoids in the tonsils, the appendix, which is not in fact useless, and pyrus patches, which you can find in your intestines. The tonsils, appendix, and pyrus patches found along your gastrointestinal tract and respiratory tract do a similar job to lymph nodes. These are extra checkpoints to ensure that what you are breathing and eating will not make you sick. The other three lymphoid organs, the thymus, spleen, and bone marrow, provide an environment for some of your immune cells to mature before being released into your body. Clearly, the lymphatic system plays an important role in keeping us all alive and well. The system literally exists in parallel with and works together with the circulatory system, ensuring that throughout our whole body, wastes and pathogens are constantly being filtered out and blood pressure is maintained.