TY - CHAP M1 - Book, Section TI - Thymoma A1 - Longo, Dan L. A2 - Kasper, Dennis A2 - Fauci, Anthony A2 - Hauser, Stephen A2 - Longo, Dan A2 - Jameson, J. Larry A2 - Loscalzo, Joseph Y1 - 2014 N1 - T2 - Harrison's Principles of Internal Medicine, 19e AB - The thymus is derived from the third and fourth pharyngeal pouches and is located in the anterior mediastinum. It is composed of epithelial and stromal cells derived from the pharyngeal pouch and lymphoid precursors derived from mesodermal cells. It is the site to which bone marrow precursors that are committed to differentiate into T cells migrate to complete their differentiation. Like many organs, it is organized into functional regions, in this case the cortex and the medulla. The cortex of the thymus contains ~85% of the lymphoid cells, and the medulla contains ~15%. It appears that the primitive bone marrow progenitors enter the thymus at the corticomedullary junction and migrate first through the cortex toward the periphery of the gland and then toward the medulla as they mature. Medullary thymocytes have a phenotype that cannot be distinguished readily from that of mature peripheral blood and lymph node T cells. SN - PB - McGraw-Hill Education CY - New York, NY Y2 - 2022/07/04 UR - accesspharmacy.mhmedical.com/content.aspx?aid=1120793444 ER -