Endocrine - Thymus Development

Embryology - 16 Apr 2024 Expand to Translate
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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.

Stieda in 1881^[1] was the ﬁrst to observe that the thymus gland originated from a visceral (pharyngeal) pouch (endoderm).

This current page relates to the endocrine role of the thymus, for more detailed description of this organ development see Thymus Development.

Historic Embryology - Endocrine
1903 Islets of Langerhans \| 1903 Pig Adrenal \| 1904 interstitial Cells \| 1908 Pancreas Different Species \| 1908 Pituitary \| 1908 Pituitary histology \| 1911 Rathke's pouch \| 1912 Suprarenal Bodies \| 1914 Suprarenal Organs \| 1915 Pharynx \| 1916 Thyroid \| 1918 Rabbit Hypophysis \| 1920 Adrenal \| 1935 Mammalian Hypophysis \| 1926 Human Hypophysis \| 1927 Adrenal \| 1927 Hypophyseal fossa \| 1930 Adrenal \| 1932 Pineal Gland and Cysts \| 1935 Hypophysis \| 1935 Pineal \| 1937 Pineal \| 1935 Parathyroid \| 1940 Adrenal \| 1941 Thyroid \| 1950 Thyroid Parathyroid Thymus \| 1957 Adrenal

| Lecture - Head Development

Historic Embryology
1909 Lymph glands \| 1912 Development of the Lymphatic System \| 1918 Gray's Lymphatic Images \| 1916 Pig Lymphatics \| 1919 Chicken Lymphatic \| 1921 Spleen \| 1922 Pig Stomach Lymphatics \| 1932 Cat Pharyngeal Tonsil \| Historic Disclaimer

Some Recent Findings

Human Embryo (week 6 - 8)^[2]

What do we know about the structure of human thymic Hassall's corpuscles? ^[3] "Hassall's corpuscles are the most prominent structures in the human thymus. However, relatively few analyses have been performed to determine their function and cellular origins during development. In this study, we evaluated the cellular microenvironment of human thymic Hassall's corpuscles using histochemistry, immunohistochemistry, and transmission electron microscopy. ... Considerable variation in the sizes, shapes, and numbers of Hassall's corpuscles was observed, even amongst children of the same age. ... Immunohistochemical staining and electron microscopy revealed that Hassall's corpuscles resemble other types of stratified squamous epithelia."

Dynamics of thymus organogenesis and colonization in early human development^[4] "The thymus is the central site of T-cell development and thus is of fundamental importance to the immune system, but little information exists regarding molecular regulation of thymus development in humans. ... In addition, we provide molecular evidence that the human thymic epithelium derives solely from the third pharyngeal pouch, as in the mouse, in contrast to previous suggestions."
Thymus-associated parathyroid hormone has two cellular origins with distinct endocrine and immunological functions^[2] "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^[5]"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 Hormones

Thymus produces self-hormones

thymulin
thymosin
thymopentin
thymus humoral factor

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 Vasculature

Like all endocrine organs the thymus is eventually richly vascularised, development has been previously summarised.^[6]

GA week 10 - initial blood supply.
GA week 12 - interlobular septa blood spaces late normoblasts and granulocytes increase, cortical and medullary vasculature increases.
GA week 16 - nerve bundles accompany arteries and veins.
GA week 20 to 24 - radial cortical capillaries drain into capsular venules. The arterioles give rise to a series of radial cortical capillaries and less regular vessels to the medulla.
GA week 28 to 40 - vascular thymic supply markedly increases and cortical capillaries can anastomose.

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^[7], 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

↑ Stieda L (1881) Untersuchungen über die Entwickelung der Glandular Thymus, Glandular Thyreoidea, und Glandular carotidica. Leipzig, Engelmann p38.
↑ ^2.0 ^2.1 <pubmed>21203493</pubmed> | PLoS Genet.
↑ <pubmed>28279759</pubmed>
↑ <pubmed>23571219</pubmed>
↑ <pubmed>20644572</pubmed>
↑ Ghali WM, Abdel-Rahman S, Nagib M & Mahran ZY. (1980). Intrinsic innervation and vasculature of pre- and post-natal human thymus. Acta Anat (Basel) , 108, 115-23. PMID: 7445948
↑ <pubmed>20354268 </pubmed>

Reviews

Articles

Search PubMed

Search Pubmed: thymus development

Additional Images

Historic Images

Historic Disclaimer - information about historic embryology pages
Pages where the terms "Historic" (textbooks, papers, people, recommendations) appear on this site, and sections within pages where this disclaimer appears, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the terminology and interpretation of the developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these terms, interpretations and recommendations may not reflect our current scientific understanding. (More? Embryology History \| Historic Embryology Papers)

Sudler, MT. The Development of the Nose and of the Pharynx and its Derivatives in Man. (1902) Amer. J. Anat 1:391–416. Thymus Gland

Fig. 8. Model of pharynx embryo CXLIV
Fig. 9. Model of pharynx embryo XLIII
Fig. 10. Lateral view of embryo XXII

Adult Histology

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

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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?

[1] Stieda L (1881) Untersuchungen über die Entwickelung der Glandular Thymus, Glandular Thyreoidea, und Glandular carotidica. Leipzig, Engelmann p38.

[PMID21203493-2] 2.0 ^2.1 <pubmed>21203493</pubmed> | PLoS Genet.

[PMID28279759-3] <pubmed>28279759</pubmed>

[PMID23571219-4] <pubmed>23571219</pubmed>

[5] <pubmed>20644572</pubmed>

[PMID7445948-6] Ghali WM, Abdel-Rahman S, Nagib M & Mahran ZY. (1980). Intrinsic innervation and vasculature of pre- and post-natal human thymus. Acta Anat (Basel) , 108, 115-23. PMID: 7445948

[7] <pubmed>20354268 </pubmed>

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