Thymus is most active during the neonatal and pre-adolescent periods. The thymus is a flat and bilobed organ located behind the stemun, above the heart. Each lobe of the thymus contains numerous lobules, separated from each other by connective tissue called septa. Each lobule is differentiate into an outer cortex and an inner medulla. Within each lobule, the devoloping T cells called thymocytes are arranged into outer cortex and inner medulla.
he inner medulla contains immature thymocytes and outer cortex has matured thymocytes. One of its main secretions is the hormone thymosin. It stimulates the cell to become mature and immunocompetent. By the early teens, the thymus begins to atrophy and is replaced by adipose tissue.