The lymphatic system is made up of two semi-independent parts; a network of lymphatic vessels and many lymphoid tissues and organs within the body (Kent, 2000).
The lymphatic system is a filter and drainage system that controls the fluid balance within the body (Kent, 2000).
During blood circulation, blood plasma seeps into tissue by means of the thin capillary walls (Encyclopædia Britannica, 2017). Blood plasma that escapes is referred to as interstitial or extracellular fluid. This fluid carries all the nutrients needed by tissue cells and removes waste product (Encyclopædia Britannica, 2017).
The walls of the capillaries are selectively permeable to many components of the blood plasma such as glucose and mineral ions (Encyclopædia Britannica, 2017). These nutrients in the tissue are low in concentration and diffuse from the plasma (Encyclopædia Britannica, 2017). Any of this fluid that’s left behind is removed from the tissue by the lymphatic vessels and returned into the blood (Encyclopædia Britannica, 2017). Not all fluid returns to the blood capillaries though some enters the lymph capillaries (Kent, 2000).
Molecules that are too big to pass through the lymph capillaries have the ability to enter the lymph system at tiny valves in their walls (Kent, 2000). The movement of liquid is done by compression caused by body movement and backflow is stopped by valves (Kent, 2000).
Whereas the lymphoid organs accommodate phagocytic cells and lymphocytes, they have a vital job in the bodies defence mechanisms and resistance to disease. (Kent 2000).
Lymphocytes are white blood cells that are produced by the lymphatic system in the lymph nodes they help defend the body from infection by engulfing and secreting antibodies to destroying the foreign particles (Kent, 2000).