Thymus (adult) (20X)

Here you see an overview of the anatomy of the thymus at 4X magnification.The speciman is from an adult person. Compared to the thymus of a child most of the thymus tissue has been replaced by adipose tissue. If you haven't looked at the child thymus yet, I urge you to do so first.

In adults, the thymus undergoes a process of involution, where the organ gradually decreases in size and its function diminishes over time. Unlike the highly active thymus of childhood, which is large and rich in lymphoid cells, the adult thymus is smaller, with a significant increase in adipose tissue replacing the lymphoid cells. This transition, which begins in early adulthood, results in a reduction in the production of new naïve T-cells, though the thymus continues to support the maturation of T-cells to a lesser extent.