The thymus gland lies in the upper part of the mediastinum behind the sternum and extends upwards into the root of the neck.
The thymus consists of two lobes joined by areolar tissue. The lobes are enclosed by a fibrous capsule which dips into their substance,dividing them into lobules that consist of an irregular branching framework of epithelial cells and lymphocytes.
ORGANS ASSOCIATED WITH THE THYMUS.
Anteriorly- sternum and upper four costal cartilages.
Posteriorly-aortic arch and its branches.
Laterally- lungs.
Superiorly- structures in the root of the neck.
Inferiorly- heart.
FUNCTION.
Lymphocytes originate from stem cells in red bone marrow. Those that enter the thymus develop into activated T-lymphocytes.
Thymic processing produces mature T-lymphocytes that can distinguish ‘self’ tissue from foreign tissue,and also provides each T-lymphocyte with the ability to react to only one specific antigen from the millions it will encounter. T-lymphocytes then leave the thymus and enter the blood. Some enter lymphoid tissues and others circulate in the bloodstream. T-lymphocytes production,although most prolific in youth,probably continues throughout life from a resident population of thymic stem cells.
