Thymus gland is a tubeless gland of brown-pink color made by flat lymphoid tissue situated behind the sternum in the upper portion of mediastinum in the chest. It remains above the heart and its main blood vessels. There are two lobes in the left and right side which are connected to each other by the connecting tissue and are closed in a capsule of connecting tissue. Each lobe is divided into small lobules by the trabeculae. There is cortex outside each lobule and medulla in the center inwards. There are several small lymphocytes in the cortex (which are often called thrombocytes) and most of lymphocytes get degenerated before emerging the thymus gland. There are only capillaries inside the thymus gland. Eosinophilic corpuscles which are called thymic corpuscles or Hassall’s corpuscles are found in the medulla. There is a substance named hyaline is present at the center of cells or corpuscles which is surrounded by the ring of connecting tissue along with epithelial cells from all around.
The thymus gland produces lymphocytes in the embryo stage and helps in building antibodies. The thymus gland is bigger comparatively (about 12 to 15 grams) and it makes antibodies in the infant and plays an important role in the early growth of immunity system or resistance power against diseases. Its size keeps on increasing from birth to puberty and it is much active in the childhood and before getting adulthood.