IMMUNE SYSTEM IN THE BODY

Immune system consists of-

• Lymphoid organs
• Lymphoid tissues
• B- cells and T-cells
• Antibodies

Lymphoid organs-

The organs where origin and/or maturation and proliferation of lymphocytes occur are called lymphoid organs.

Lymphoid organs are of two types-

1. Primary lymphoid organs

2. Secondary lymphoid organs.

The primary lymphoid organs are bone marrow and thymus where immature lymphocytes differentiate into antigen-sensitive lymphocytes.

The bone marrow is the main lymphoid organ where all blood cells including lymphocytes are produced.

The thymus is a lobed organ located near the heart and beneath the breastbone.

Spleen, tonsil, lymph node, Peyer’s patches of small intestine and appendix are secondary lymphoid organs where proliferation of lymphocytes take place.

The secondary lymphoid organs provide the sites for interaction of lymphocytes with the antigen, which then proliferate to become effector cells.

The spleen is a large bean shaped organ mainly contains lymphocytes and phagocytes which acts as a filter of the blood by trapping blood-borne microorganisms and has a large reservoir of erythrocytes.

The lymph nodes are small solid structures located at different points along the lymphatic system.

Lymph nodes serve to trap the antigens and these antigens trapped are responsible for the activation of lymphocytes and cause the immune response.

Fig. lymphoid organs  

Lymphoid tissue-

Lymphoid tissue are located within the lining of the respiratory, digestive and urogenital tracts.

Lymphoid tissues are also called mucosalassociated lymphoid tissue (MALT) which constitutes about 50 per cent ofthe lymphoid tissue in human body.