Right lobe of thymus

At a glance

English

Right lobe of thymus

Latin (TA2)

Lobus dexter thymi

System

Lymphoid organ

Region

Trunk

Side

Single, on the midline

About the right lobe of thymus

The thymus consists of a right and a left lobe placed side by side behind the sternum and bound together in the midline by fibrous tissue. The right lobe occupies the right half of the gland in the superior mediastinum and frequently continues down into the anterior mediastinum over the front of the pericardium. Its upper pole tapers and may reach into the root of the neck. The lobes differ in size from person to person, so neither side is consistently the bigger.

On its deep side the right lobe rests on the superior vena cava and the right brachiocephalic vein, with the ascending aorta and the brachiocephalic trunk close by and the pericardium lower down. Its front faces the manubrium and body of the sternum, and laterally it is overlapped by the right pleura and the anterior border of the right lung. A delicate capsule surrounds the lobe and sends septa inwards, breaking it into lobules. Each lobule has a deeply staining cortex full of immature T cells and a lighter medulla with a network of epithelial cells and scattered thymic corpuscles.

Its role is the education of T lymphocytes. Stem cells from the bone marrow settle in the cortex, proliferate and are screened as they migrate to the medulla. Only those that can work with the body's own tissue-type molecules, without attacking self tissues, are allowed to leave; most are removed in the process. The gland is most active in early life, reaches its greatest weight in the early teens and afterwards gradually shrinks and fills with fat, though it continues to export some new T cells.

In infants the lobe may be large enough to produce a sail-shaped shadow beside the heart on a chest X-ray, a normal finding. Thymomas and thymic cysts can arise in either lobe and may press on the great veins; thymoma is often linked to myasthenia gravis. The thymus is approached through the sternum when it has to be removed.

Function and supply

Function

Supports the maturation and selection of T lymphocytes and releases thymic hormones that promote their development.

Nerve supply

Twigs from the vagus nerves and the sympathetic trunk, chiefly following its blood vessels.

Blood supply

Thymic branches of the internal thoracic artery, helped by the inferior thyroid and pericardiacophrenic arteries; thymic veins drain to the left brachiocephalic vein and the internal thoracic veins.