The lymphatic system is a vast network of tubes (lymph vessels) which are filled with a white liquid (lymph). Lymph comes from the general liquids found in the body and from blood which has been leaked from blood vessles. Lymph slowly trundles through the body, delivering nutirents to body tissues and collects the waste from tissues.
At various points around the body, the lymph collects and forms lymph nodes. These are usually the size of a pea, but when ill, they can swell up, sometimes to the size of a golf ball.
This is due to the other important function of the lymphatic system, which is as a breeding ground for white cells. When the body is ill, the lymph nodes go into overdrive, producing billions of white cells which then fight the germs which are attacking the body. The lymph nodes also collect dead germs, so that they do not travel through the body. So the lymphatic system s important in maintaining good health.

 Some tissue fluid (colorless fluid thus accumulated in the intercellular spaces) present in the intercellular spaces enters the blind lymphatic capillaries (lacteals). After tissue fluid has entered the, it is now called lymph. The excess tissue fluid is returned to the blood through the lymphatic system. This system consists of an extensive network of thin walled vessels, the lymph capillaries.

The lymphatic system is quite distinct from the blood vascular system. The lymph capillaries have valves in their walls which allow the tissue fluid to enter the lymph capillaries but it prevent its flow out of them. These capillaries join together to form the big vessels, called the lymph vessels forming the lymphatic system. The lymphatic system serves as an accessory drainage system of the body by removing the excess fluid and dissolved substances that leak from the blood capillaries.

The larger lymphatic vessels join the subclavian veins and pour their fluid into them. This is how the lymph is returned to the circulatory system. The lymphatic system transports fats from the intestine to the blood stream. It also helps in defending against the attacks of bacteria and viruses by filtering or destroying them at special sites called the lymph nodes.