The thymus gland is a small organ behind the breastbone that plays an important function both in the immune system and endocrine system.
The growth and development of thymus continues until puberty. There are two distinct cell types within the thymus i.e. the lymphoid cells (thymocytes) and the reticular epithelial cells. In children, T cells densely populate the cortex of the thymus. As the T cells develop they pass to the medulla, before they are released into the circulation.
Within the thymus, T cells mature. T cells are critical to the adaptive immune system, where the body adapts specifically to foreign invaders. The thymus is composed of two identical lobes and is located anatomically in the anterior superior mediastinum, in front of the heart and behind the sternum.