Hassall's corpuscles

Hassall's corpuscles are distinctive structures found in the thymus gland, specifically within the medulla of the thymic lobules. They are named after the British physician and anatomist Arthur Hill Hassall, who first described them in 1846.

Structure

Hassall's corpuscles are composed of concentric layers of epithelial cells that are often keratinized. These cells are derived from the endoderm of the third pharyngeal pouch. The central core of the corpuscles may contain keratohyalin granules, and in some cases, they may undergo calcification.

Function

The exact function of Hassall's corpuscles is not entirely understood, but they are believed to play a role in the maturation of T cells (thymocytes). They are thought to be involved in the process of negative selection, which eliminates autoreactive T cells that could potentially cause autoimmune diseases. Additionally, Hassall's corpuscles may secrete cytokines that influence the development of regulatory T cells.

Clinical Significance

Changes in the number and structure of Hassall's corpuscles can be observed in various thymic diseases and conditions. For instance, in thymic hyperplasia, there is an increase in the number of Hassall's corpuscles. Conversely, in thymic atrophy, such as that seen in DiGeorge syndrome, the number of Hassall's corpuscles is significantly reduced.

Histology

Under the microscope, Hassall's corpuscles appear as eosinophilic, spherical structures within the medulla of the thymus. They are surrounded by a network of reticular cells and thymocytes. The concentric arrangement of epithelial cells is a key histological feature that distinguishes Hassall's corpuscles from other structures in the thymus.

See Also

• Thymus
• T cell
• Thymic epithelial cell
• Negative selection
• Autoimmune disease