The thymus gland is a lobular structure located on the dorsal side of the heart and the aorta. The thymus plays a major role in the development of the immune system.
This gland secretes the peptide hormones called thymosins. Thymosins play a major role in the differentiation of Tlymphocytes, which provide cell-mediated immunity.
In addition, thymosins also promote production of antibodies to provide humoral immunity. Thymus is degenerated in old individuals resulting in a decreased production of thymosins. As a result, the immune responses of old persons become weak.