GENERAL HISTOLOGY

Detailed explanation-1: -THE THYMUS IS A SPECIALIZED ORGAN THAT DIRECTS THE DEVELOPMENT AND SELECTION OF T CELLS WHICH DIRECT ADAPTIVE IMMUNITY. THYMIC FUNCTION IS SPATIALLY AND TEMPORALLY REGULATED AND WANES WITH AGE. THYMIC OUTPUT IS ESSENTIAL DURING EARLY LIFE TO ESTABLISH IMMUNE COMPETENCE AND HOMEOSTASIS BUT IS DISPENSABLE THEREAFTER.

Detailed explanation-2: -The thymus develops from the third pharyngeal pouch, which gives rise to endodermal-derived thymic cortical epithelium, and the third pharyngeal cleft, which is thought to give rise to ectodermal-derived medullary thymic epithelium.

Detailed explanation-3: -The thymus gland is a small organ that lies in the upper chest under the breastbone. It makes white blood cells, called lymphocytes, which protect the body against infections.

Detailed explanation-4: -The NK/T precursors migrate to the thymus, where thymocyte development proceeds in three multipartite phases: the DN phase (neither CD4 nor CD8 appears on the thymocyte surface), the DP phase (both CD4 and CD8 are present), and the SP phase (either CD4 or CD8 is present on the surface of a mature T cell).

Detailed explanation-5: -Three major thymus hormones, thymosin, thymopoietin, and thymulin, are thought to reside in the cytoplasm of the thymus epithelial cell.