The medulla is the inner area of the lobule, whereas the outer area is called the cortex. Immature T-lymphocytes stay in the cortex region, whereas the medulla region contains the mature T-lymphocytes. Only the mature cells can identify foreign cells.
The gland has a thin outer covering and consists of three different types of cells–lymphocytes, epithelial cells, and neuroendocrine cells. Epithelial cells give structure to the thymus, neuroendocrine cells release hormones, and lymphocytes protect you against infections.