Organ
Thymus
A specialized environment for developing T cells
High-yield
Positive selection retains cells able to recognize self-MHC; negative selection limits strongly self-reactive cells. Loss of developing cells is not all caused by self-reactivity.
Overview
Thymic tissue supports T-cell development within epithelial compartments in the anterior chest. A cellular cortex surrounds medullary regions containing Hassall corpuscles. With age, functional tissue becomes increasingly interspersed with fat.
Reference facts
- Location
- Behind the upper sternum and in front of the great vessels and pericardium; cervical extensions can occur
- Parts
- Usually two lobes containing cortical and medullary tissue, with epithelial Hassall corpuscles in the medulla
- Blood supply
- Variable branches, commonly from internal thoracic and inferior thyroid arteries
- Venous/Lymphatic drainage
- Venous routes commonly reach left brachiocephalic and internal thoracic veins; outgoing lymphatics reach regional thoracic nodes, without the afferent arrangement of a lymph node
- Function
- Supports T-cell maturation, receptor selection and development of immune tolerance
- Hormones
- Thymic cells produce peptides and other signaling molecules; thymosin-related components and growth peptides have been studied in human tissue
- Innervation
- Sympathetic fibers accompany vessels and enter thymic tissue. Direct vagal innervation remains disputed and should not be presented as established
Clinical correlation
Thymic hyperplasia and thymoma are associated with myasthenia gravis. A mass in the anterior mediastinum has other possible causes, so location alone does not establish thymic disease.
Frequently asked questions
Where is the thymus located?
Behind the upper sternum and in front of the great vessels and pericardium; cervical extensions can occur.
What does the thymus do?
Supports T-cell maturation, receptor selection and development of immune tolerance.
What are the parts of the thymus?
Usually two lobes containing cortical and medullary tissue, with epithelial Hassall corpuscles in the medulla.
What is the blood supply of the thymus?
The thymus is supplied by the variable branches, commonly from internal thoracic and inferior thyroid arteries.