These organs of the immune system produce, develop and disseminate the lymphocytes, one of five types of white blood cells, which will recognise and fight infection and diseases. 

The blood and lymphatic vessels are an important part of the lymphoid organs because they carry the lymphocytes to and from different parts of the body.

 Lymphoid Organs

Bone marrow : This is the soft tissue in the hollow centre of bones. All blood cells including most immune cells, are produced within the bone marrow from special cells called stem cells. Once they have matured they migrate to various parts of the immune system via the lymphatic system.

Thymus : This pinkish gray gland is located behind the breast bone. Its main function is to transform the white blood cells into the various type of T-cells which are able to mount an attack on the organisms. The thymus is most active upto adolescence, after which it begins to grow smaller.

Tonsils : Lymph tissue are also found around the entrance to the throat, the most obvious being the tonsil. Tonsils trap and destroy bacteria and germs that we inhale or swallow. They show signs of infection when they have white patches or a pale yellow substance covering them.

Spleen : This fist-size, spongy and deep red organ is located on the left side of the abdominal cavity just behind the lower rib. It cleanses our blood by filtering used-up and defective red blood cells. It also cleanses the phagocytes that fight infection. Large numbers of lymphocytes and antibodies also reside here on the lookout for invaders.

 Lymphatic System



The rest of the organs of the immune system is made up of the lymphatic system which acts like a filtering system sifting and destroying bacteria, abnormal cells and other foreign bodies. It is made up of the lymph and lymph nodes.

  • Lymph : This clear fluid seeps from our blood vessel into our tissues, collecting cell debris, bacteria and unwanted stuff along the way. Most of these fluid flows back into the blood system while the rest circulates back to the heart. 

    The lymph is pushed along by movements of muscles, pressures within our chests as we breathe and the pulses of nearby arteries.
  • Lymph nodes : These are gland like organs found in many sites in the body, including under the arms, behind the ears, in the neck, abdomen and the groin. The lymph nodes are home to macrophages, T cells and B cells.

    It’s main function is to “sanitise” the lymph. They act like filters collecting microbes and other foreign material that has been washed from our tissues by the lymph.

    The macrophages invest the germs and anything else that is not wanted by the body, thus keeping them out of the bloodstream. When we have “swollen glands” it means that our lymph nodes are inflamed and it is fighting to contain an infection from spreading to the other parts of the body.

With these three defensive system – innate, adaptive and the lypmhatic system – the immune system is complex and amazing. 

When the organs of the immune system are working properly, it fights off potential disease and infections which we may never even know we’ve been exposed to. To this extent we must acknowledge that if our immune systems viz the organs of the immune system and the cells involved are healthy, so are we.