Thymus Development

Introduction

The thymus has a key role in the development of an effective immune system as well as an endocrine function.

The mature thymus epithelium has two main cell types: cortical thymic epithelial (cTECs) and medullary thymic epithelial cells (mTECs) or stromal cells. These thymic stromal cells provide signals for T cell differentiation.

Links: original Endocrine Development - Thymus page

Development Overview

The thymus and parathyroid are derived from 3rd pharyngeal pouches.

Development is a series of epithelial/mesenchymal inductive interactions between neural crest-derived arch mesenchyme and pouch endoderm. There is also the possibility that the surface ectoderm of 3rd pharyngeal clefts participates in thymus development.

Hassall's bodies form between 6 and 10 lunar months in humans. They appear after lymphopoiesis has been established and the cortex, medulla and the cortico-medullary junction are able to select of T lymphocytes undergoing progressive maturation. (Text modified from Bodey and Kaiser, 1997)

Experimental studies have shown that a neural crest contribution is also required during early thymic organogenesis.

Hassall's Bodies

Hassall's bodies, also called Hassall's corpuscles, form between 6 and 10 lunar months in humans. They appear after lymphopoiesis has been established and the cortex, medulla and the cortico-medullary junction are able to select of T lymphocytes undergoing progressive maturation.Within the thymus their number increases until puberty, then decreases.

Named after Arthur Hill Hassall (1817-1894) a British physician and chemist.

Molecular Development

Eya - human homolog of the Drosophila 'eyes absent' (Eya) gene.

Six - vertebrate genes which are homologs of the Drosophila 'sine oculis' (so) gene.

Zou D, Silvius D, Davenport J, Grifone R, Maire P, Xu PX. Patterning of the third pharyngeal pouch into thymus/parathyroid by Six and Eya1. Dev Biol. 2006 May 15;293(2):499-512. | Xu PX, Zheng W, Laclef C, Maire P, Maas RL, Peters H, Xu X. Eya1 is required for the morphogenesis of mammalian thymus, parathyroid and thyroid. Development. 2002 Jul;129(13):3033-44.

References

The development of the fetal thymus: an in utero sonographic evaluation. Zalel Y, Gamzu R, Mashiach S, Achiron R. Prenat Diagn. 2002 Feb;22(2):114-7. PMID: 11857615

Glossary Links

Glossary: A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Numbers | Symbols | Term Link

Cite this page: Hill, M.A. (2024, May 23) Embryology Thymus Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Thymus_Development

What Links Here?