Endocrine - Thymus Development

Introduction

Embryonic origins of the endocrine organs of the neck

The thymus has two origins for the lymphoid thymocytes and the thymic epithelial cells. The thymic epithelium begins as two flask-shape endodermal diverticula that form from the third pharyngeal pouch and extend lateralward and backward into the surrounding mesoderm and neural crest-derived mesenchyme in front of the ventral aorta. The immune system T cells are essential for responses against infections and much research concerns the postnatal development of T cells within the thymus.

--Mark Hill 21:01, 21 February 2011 (EST) This current page relates to the endocrine role of the thymus, for more detailed description of this organ development see Thymus Development.

| Lecture - Head Development

Some Recent Findings

Human Embryo (week 6 - 8)

Thymus-associated parathyroid hormone has two cellular origins with distinct endocrine and immunological functions "In mammals, parathyroid hormone (PTH) is a key regulator of extracellular calcium and inorganic phosphorus homeostasis. Although the parathyroid glands were thought to be the only source of PTH, extra-parathyroid PTH production in the thymus, which shares a common origin with parathyroids during organogenesis, has been proposed to provide an auxiliary source of PTH, resulting in a higher than expected survival rate for aparathyroid Gcm2⁻/⁻ mutants. However, the developmental ontogeny and cellular identity of these "thymic" PTH-expressing cells is unknown. ...Our data show conclusively that the thymus does not serve as an auxiliary source of either serum PTH or parathyroid function. We further show that the normal process of parathyroid organogenesis in both mice and humans leads to the generation of multiple small parathyroid clusters in addition to the main parathyroid glands, that are the likely source of physiologically relevant "thymic PTH."" Endocrine - Parathyroid Development Decision checkpoints in the thymus"The development of T cells in the thymus involves several differentiation and proliferation events, during which hematopoietic precursors give rise to T cells ready to respond to antigen stimulation and undergo effector differentiation."

More recent papers

This table allows an automated computer search of the external PubMed database using the listed "Search term" text link. This search now requires a manual link as the original PubMed extension has been disabled. The displayed list of references do not reflect any editorial selection of material based on content or relevance. References also appear on this list based upon the date of the actual page viewing. References listed on the rest of the content page and the associated discussion page (listed under the publication year sub-headings) do include some editorial selection based upon both relevance and availability. More? References | Discussion Page | Journal Searches | 2019 References | 2020 References Search term: Thymus Embryology <pubmed limit=5>Thymus Embryology</pubmed>

Thymus Development

Developing Human (stage 22)

Developing Human Thymus (stage 22)

• Endoderm - third pharyngeal pouch
• Week 6 - diverticulum elongates, hollow then solid, ventral cell proliferation
• Thymic primordia - surrounded by neural crest mesenchyme, epithelia/mesenchyme interaction

• Thymus - bone-marrow lymphocyte precursors become thymocytes, and subsequently mature into T lymphocytes (T cells)
• Thymus hormones - thymosins stimulate the development and differentiation of T lymphocytes

B2 Pharyngeal Arch Pouches 3 and 4 (stage 13)	D1 Developing Human Thymus (stage 22)

Thymus Involution

A postnatal process defined as a decrease in the size, weight and activity of the gland with advancing age. In a recent review, thymic involution was described as a result of high levels of circulating sex hormones, in particular during puberty, and a lower population of precursor cells from the bone marrow and finally changes in the thymic microenvironment.

References

Reviews

<pubmed>19582736</pubmed> <pubmed>18304000</pubmed> <pubmed>17876091</pubmed> <pubmed>16448532</pubmed>

Articles

<pubmed>17625108</pubmed>

Search PubMed

Search April 2010

• Endocrine Development - All (14277) Review (4620) Free Full Text (3140)

Search Pubmed: thymus development

Terms

• Hassall's corpuscle - thymic corpuscle.
• Thymic corpuscle (=Hassall's corpuscle) a mass of concentric epithelioreticular cells found in the thymus. The number present and size tend to increase with thymus age. (see classical description of Hammar, J. A. 1903 Zur Histogenese und Involution der Thymusdriise. Anat. Anz., 27: 1909 Fiinfzig Jahre Thymusforschung. Ergebn. Anat. Entwickl-gesch. 19: 1-274.)
• thymic epitheliocytes - reticular cells located in the thymus cortex that ensheathe the cortical capillaries, creating and maintain the microenvironment necessary for the development of T-lymphocytes in the cortex.
• T lymphocyte (cell) - named after thymus, where they develop, the active cell is responsible for cell-mediated immunity. (More? Electron micrographs of nonactivate and activated lymphocytes)

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, April 16) Embryology Endocrine - Thymus Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Endocrine_-_Thymus_Development

What Links Here?

© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G