All issues > Volume 34(8); 1991

Original Article

J Korean Pediatr Soc. 1991;34(8):1057-1069. Published online August 31, 1991.

Weight and morphologic development of prenatal human thymus.

Il Soo Ha¹, Kwang Wook Ko¹, Je Geun Chi²

¹Department of Pediatrics, Seoul National University College of Medicine, Seoul, Korea
²Department of Pathology, Seoul National University College of Medicine, Seoul, Korea

Received: July 26, 1991;  Accepted: July 26, 1991.

Abstract

Thymus is a primary lymphoid organ which has an important role in maturation of immune competence. This organ matures earlier than the other organs, and the informations about its prenatal development are essential to understand the maturation of human immunity. To delineate the weight and morphologic development of prenatal thymus, the authors measured the weight of 221, and observed gross and histologic features of 262 human embryonal and fetal thymuses. Weight of the thymuses increased exponentially with gestational age (from 0.06 g at the 11 〜 14th week to 13.54 g at the 35—38th week), though their ratio to body weight reached a plateau at the 27—30 th week. The thymic primordia developed from the 3rd pharyngeal pouch at late 6th week, and moved into the superior mediastinum (its permanent position) with obliteration of internal canal at the 8th week. Infiltration of lymphocytes and lobulation of thymus began at 9th week, followed by demarca- tion between cortex and medulla, appearance of subcapsular light zone at 10th week. HassalFs body first appeared at 13th week, after when quantitative changes predominated. From the 18th week, septal granulopoiesis was noted, and scattered cortical macrophages were observed since the 30th week.

Keywords :Fetus;Thymus;Ontogeny;Weight;Morphology