Question

(a) Highlight the role of thymus as a lymphoid organ.
(b) Name the cells that are released from the above mentioned gland. Mention how they help in immunity.

Answer 1

Hint: Thymus is a specialised primary lymphoid organ of the body’s immune system and which is involved in maturation of specialised immune cells.

Complete answer:
A. The thymus is a specialized primary lymphoid organ of the immune system. It is the site responsible for the maturation of T-cells. Thymus gland is located in the upper front part of the chest, in the anterior superior mediastinum, behind the sternum, and in front of the heart. The thymus consists of immature T cells called thymocytes.The thymus gland is found to be most largest and active during the neonatal and pre-adolescent periods. Thymus activity and size reduce upon reaching teenage. T cells are formed from their hematopoietic precursors in the bone marrow from which they migrate to thymus for their maturation. T-cell maturation ensures that these cells react again to the foreign antigen, not the antigen of their own body. Once they mature, they move into the lymphatic system for immune response.

B. T cells are produced by the thymus gland upon maturation. T-cell maturation occurs in the thymus gland which forms a major part of the cell-mediated immunity of the immune system. T-cells are one the two primary lymphocytes. The other class is B cell lymphocytes. These lymphocytes help in determining the specificity of the immune response towards the specific antigen. T-cells differentiate into helper, regulatory and cytotoxic cells or become memory T-cells. They cannot produce antibodies on their own but they regulate antibody production against the antigen through B-cells which have the ability to produce antibodies against the antigen.They generally circulate in the lymphatic system and upon stimulation by antigens, T-helper cells secrete chemical messengers called cytokines. These cytokines trigger the B-cells to produce plasma cells which produce the antibodies against the antigen. Cytotoxic T cells are those cells which directly bind to infected cells and kill them including the cancer cells.

Note: Thymus gland is made up of two lobes, each consisting of a central medulla and an outer cortex, surrounded by a capsule.