Thusomer

from Wikipedia, the free encyclopedia

In embryology, thusomeres are loose cell clusters of the paraxial mesoderm , which can be distinguished by electron microscopy as metameric segmentations during the embryonic development of vertebrates , in the head area without the typical somites deposits in the surface epithelium.

They appear around the middle of the third week of development as paired mesenchyme segments on both sides along the neural tube , from cranial to caudal, depending on the species, up to 50 segments. While in humans the first seven thusomer pairs - which do not form somites - form mesoblasts of the pharyngeal arches and contribute to external eye muscles , facial and masticatory muscles, the other 42–44 pairs of somites initially develop , from the 25th day about 3–4 daily . In humans, several caudals are then regressed, so that 35–37 remain.

There are still controversial scientific discussions about the existence, origin and meaning of the thusomers and their differentiation from somites.

Web links

Commons : Embryology  - collection of images, videos and audio files

Individual evidence

  1. ↑ a b S. Kuratani, T. Schilling: Head segmentation in vertebrates. In: Integrative and comparative biology. Volume 48, Number 5, November 2008, pp. 604-610, doi : 10.1093 / icb / icn036 , PMID 20607135 , PMC 2895339 (free full text).
  2. ↑ Thomas W. Sadler (edit.), Jan Langman (start.): Medical Embryology. Normal human development and its malformations. 10th edition. Thieme Verlag, Stuttgart, 2003, ISBN 3-13-446610-4 , p. 172 ff.
  3. ↑ Human Embryology - Embryogenesis, Chapter 7.2 The three-leaved germinal disc (3rd week)

swell

  • AG Jacobson: Thusomeres: mesodermal segments of vertebrate embryos. In: Development. 104 Suppl. 1988, pp. 209-220.
  • AG Jacobson: Thusomeres: mesodermal segments of the head and trunk. In: J. Hanken, BK Hall (ed.): The skull. Vol. 1, Chicago Press, Chicago (IL) 1993, ISBN 0-226-31567-3 , pp. 42-76.