Introduction to the lymphatic system

The lymphatic system may be the most underrated system of the human body. It protects the body from invaders, maintains the fluid level in the body, and absorbs dietary fat from the intestine.That’s pretty amazing for a system that is really small, sometimes even microscopic!

Now, the lymphatic system is composed of lymph, lymphocytes, lymphatic vessels and plexuses, lymph nodes and other lymphoid organs. Lymphoid organs are the part of the lymphatic system that are directly involved in the immune system because they produce lymphocytes, as is the case with the thymus and bone marrow and house lymphocytes - and other white blood cells - that are ready to respond to pathogens, as is the case with lymph nodes, the spleen and tonsils.

But we are going to focus on the role of the lymphatic system in returning leaked fluid to the blood, so let’s start by turning our attention to lymph and lymphatic vessels.

Lymph is a clear - or slightly yellow - fluid that is transported through tubes similar to blood vessels, called lymphatic vessels. Now, you may be wondering, where does this lymph come from? Well, it all starts at a network of tiny blood vessels called the capillary beds where nutrient and gas exchange occurs. During this process, around 10% of this fluid is lost and ends up in the extracellular space, which is where the lymphatic system kicks in. This fluid will be taken up first by lymphatic capillaries which are small, porous capillaries throughout the body that form lymphatic plexuses. Once this fluid enters the lymphatic capillaries, it’s called lymph. Now, the small lymphatic capillaries merge to form the next part of the lymphatic system, called lymphatic vessels. Lymphatic vessels drain lymph through lymph nodes and eventually into lymphatic trunks, which drain large regions of the body - like the subclavian trunks that drain the upper limbs. Finally, lymphatic trunks converge to form two bigger channels called lymphatic ducts, specifically the right lymphatic duct and the thoracic duct.