Lymphoid organs

Organs associated with immune system are lymphoid organs.[1]

There are two types of lymphoid organs:-

• Primary lymphoid organs
• Secondary lymphoid organs

Primary lymphoid organs (central lymphoid system)

Primary lymphoid organs are site of hemopoiesis. They produce progenitor cells which are non functional till they get a antegenic stimulus.Lymphocytes produced here moves to secondary lymphoid organs where they get antigenic stimulus and the cells become functional.the primary lymphoid organs are:-

1. THYMUS
2. Bursa of fabricius (only in birds)
3. BONE MARROW

It is the organ present above 1st sternae and below thyroid. This organ produces T lymphocytes. It brings about cell mediated immunity, graft rejection.

Bone marrow [2]

Flexible tissue in the bone interior.This organ acts both as primary and secondary lymphoid organs.this is the site of production of B lymphocytes.

Secondary lymphoid organs (peripheral lymphoid system)

Maintenance of naive and mature lymphocytes takes place here.Initiation of adaptive immune response and activation of lymphocyte by antigen occurs .the three secondary lymphoid organs are as follows:-

1. LYMPH NODE
2. SPLEEN
3. MALT (Mucosa associated lymphoid tissue)

lymph node [3]

It is small bean shaped structure which carries lymph fluid, nutrients and waste materials between body tissues and blood stream.

Spleen [4]

It is the organ present in the abdominal cavity.Filtering of blood takes place here.Old RBCs gets regenerated here.WBCs ,RBCs and platelets gets stored here.

MALT

It is the diffuse system of small concentrations of lymphoid tissue found in various submucosal membrane sites of body such as gastro intestinal tract, thyroid, breast, salivary gland, eye and skin.

Tonsils and payer's patch of small intestine are the major tissues belonging to MALT .