Lymphatic System

The lymphatic system is the body's drainage and defence network: lymphatic capillaries and vessels, lymph nodes, the spleen, thymus, tonsils and marrow, plus lymphoid tissue in the gut. It returns leaked tissue fluid to the blood (preventing swelling), absorbs dietary fats, and houses the lymphocytes that recognise and fight infection and abnormal cells. Unlike the circulation it has no central pump, relying on movement, breathing and one-way valves.

Key facts

The system returns several litres of fluid to the blood daily; without it, tissues would swell within hours.
Its vessels are the routes by which many cancers first spread to regional nodes.
The spleen filters blood while nodes filter lymph — two complementary checkpoints.
Exercise is a genuine lymphatic medicine: muscle contractions are its main pump.

What can go wrong

When the system is blocked or overloaded, swelling (lymphoedema) results — after cancer surgery or radiotherapy, or from infections. Immune weakness arises when its organs fail, as when the spleen is removed or the thymus is absent. Cancers of lymphocytes themselves (lymphomas) arise in this system and typically present as painless enlarging nodes.

Related conditions

Cancer

Related symptoms

Frequently asked questions

How is the lymphatic system different from the circulation?

It is a one-way drainage system without its own pump: it collects fluid from tissues and returns it to the veins, rather than cycling it in a loop from the heart.

Why do surgeons remove lymph nodes in cancer operations?

Because nodes are the first filter for spreading cancer cells; examining them stages the disease and guides whether further treatment is needed.

Educational information only. This atlas explains normal anatomy and describes conditions in general terms; it is not medical advice and does not replace assessment by a qualified clinician. If you have symptoms that worry you, seek medical care.