embryology

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Human embryo (around five weeks old)

The Embryology (from ancient Greek ἔμβρυον embryon , German , unborn fetus' and -logie ) is that branch of developmental biology that deals with the development of the fertilized egg and the resulting embryo busy. One also speaks of prenatal developmental biology.

In medicine and zoology , embryology subsequently also treats the growth of the fetus .

history

Greek scholars of the 5th and 4th centuries BC The first theories about the development of the embryo date back to the 4th century BC. These were shaped by the idea that it was an act of divine creation. Here took Aristotle that by sperm will activate the menstrual blood and to Initiate embryonic development. The Greek doctor Galenos described prenatal development and extraembryonic structures such as the placenta in his work On the Formation of the Fetus in the 2nd century AD . These teachings have shaped embryology up to modern times. Leonardo da Vinci made the first measurements of various stages of embryonic development . Girolamo Fabricio published early scientific studies of embryos from Acquapendente 1600 onwards for mammalian, reptile and shark embryos ( De formato foetu ) and in 1621 on the formation of eggs and chicks ( De formatione ovi et pulli ). This procedure was specified by William Harvey by studying the development of chicken embryos in the middle of the 17th century using simple magnifying lenses. Harvey also researched the development of the fallow deer , in which he could not detect any early embryonic stages. From this he wrongly concluded that the uterus secrete the embryos. It was refuted in 1672 by Reinier de Graaf , who discovered small chambers in the uterus of rabbits using the first microscope. He concluded that these could not have come from the uterus, but from other organs that he called ovaries . In these he also discovered the mature egg follicles ( Graaf's follicles ) named after him .

The discovery of a supposedly preformed chick in an unfertilized egg by Marcello Malpighi and the discovery of the sperm gave rise to a contradiction to the previous theory of epigenesis . The advocates of the preformation theory assumed that either in the egg cell or in the sperm the human was already present in a tiny format and only had to grow. The preformation theory established itself and was only heavily criticized by Caspar Friedrich Wolff in 1759 , when he was able to show that embryos develop from small spherical structures and that the embryos described by Malpighi could not be found in chicken eggs. Wolff assumed that the division and differentiation of a cell would give rise to germ layers from which the embryo would then develop.

The German doctor Robert Remak is considered the founder of modern embryology . In 1842 he described the three cotyledons ectoderm, mesoderm and endoderm. Before Rudolf Virchow and Theodor Schwann, he recognized the cell nucleus as the basic structure of cell division. Remak described the basic structure of the axon and the Remak ganglion. Later he worked in the field of galvanotherapy. In 1878, the Viennese embryologist Samuel Leopold Schenk undertook the first, not yet successful, attempt at in vitro fertilization on the semen and egg cells of rabbits and guinea pigs at the University of Vienna .

From the beginning of the 19th century, more scientists concentrated on the term "germ leaf" introduced by Wolff. Established on this basis Étienne Geoffroy Saint-Hilaire , his son Isidore Saint-Hilaire and Johann Friedrich Meckel the study of developmental disorders by reproductive toxins ( Teratology ). Christian Heinrich Pander's discovery that there are three different germ layers and Karl Ernst von Baer's discovery of the egg cell confirmed the assumed germ layer concept and the underlying epigenesis theory.

Development phases in humans

At the beginning of the development of a person is the gametogenesis . A gamete is a cell that has arisen from primordial germ cells and has a haploid set of chromosomes . If a male gamete cell ( sperm ) meets a female gamete cell ( egg cell , oocyte) during conception , fertilization (impregnation) can occur.

The development of the zygote in the first two weeks after fertilization is called blastogenesis . This is also where the embedding ( nidation or implantation) of the germ takes place (on the 6th or 7th day).

Embryogenesis is a fluid transition to this. It describes the differentiation of the different cell layers up to the fetus. It begins around the third week pc (post conceptionem) and can be linked to the formation of the third cotyledon among other things. As a result of embryogenesis, almost all organs are basically laid out and the uteroplacental circulation is developed.

From the ninth week of development until birth, one speaks of a fetus instead of an embryo. During fetogenesis , the organs created during embryogenesis grow and differentiate further.

See also

literature

  • Bruno Bloch : The historical foundations of embryology up to Harvey. In: Nova acta. Treatises of the Imperial Leopoldine-Carolinian German Academy of Natural Scientists. Volume 80, No. 3, (Halle an der Saale) 1904, pp. 215–334.
  • Paul Rother, Dietmar Wendler, R. Luther: Embryology of the people . 5th edition. Scientific scripts, Auerbach 2004, ISBN 3-928921-01-0 .
  • Keith L. Moore, T. Vidhya N. Persaud: Embryology: stages of development, early development, organogenesis, clinic . 5th edition. Elsevier, Urban & Fischer-Verlag, Munich 2007, ISBN 978-3-437-41112-0 , pp. 11-14 .
  • Ronan O'Rahilly, Fabiola Müller: Embryology and teratology of humans . 1st edition. Verlag Hans Huber, Bern 1999, ISBN 3-456-82821-7 , p. 17-19 .
  • Erich Blechschmidt: The early development of humans - an introduction . 1st edition. Kiener Verlag, Munich 2011, ISBN 978-3-943324-00-6 , pp. 240 .
  • Erich Blechschmidt: Ontogenesis of the human being - kinetic anatomy . 1st edition. Kiener Verlag, Munich 2012, ISBN 978-3-943324-03-7 , pp. 222 .
  • Keith L. Moore, T. Vidhya N. Persaud: Embryology: stages of development, early development, organogenesis, clinic . 5th edition. Elsevier, Urban & Fischer-Verlag, Munich 2007, ISBN 978-3-437-41112-0 , pp. 11-14 .
  • Ursula Weisser: Ibn Qaiyim al-Ǧauzīya on the methods of embryology. In: Medicine-historical journal. 16, 1981, pp. 227-239.
  • Janina Wellmann: The form of becoming: a cultural history of embryology 1760-1830 . Wallstein, Göttingen 2010, ISBN 978-3-8353-0594-6 .
  • Christian Girod: History of Embryology. In: Illustrated History of Medicine. German adaptation by Richard Toellner et al., Special edition Salzburg 1986, IV, pp. 1894–1943.
  • Ulrich Drews: Pocket Atlas of Embryology - 176 color tables by Astried Rothenburger and Rüdiger Gay , 2nd unchanged edition, Thieme Verlag, Stuttgart 2006, ISBN 978-3-13-109902-0 .

Web links

Wiktionary: Embryology  - explanations of meanings, word origins, synonyms, translations
Commons : Embryology  - collection of images, videos and audio files

Individual evidence

  1. ↑ GEMOLL : Greek-German school and manual dictionary.
  2. ↑ See also Ursula Weisser : Conception, inheritance and prenatal development in medicine in the Arab-Islamic Middle Ages. Erlangen 1983.
  3. ↑ Christoph Schweikardt: Embryology (modern times). In: Werner E. Gerabek , Bernhard D. Haage, Gundolf Keil , Wolfgang Wegner (eds.): Enzyklopädie Medizingeschichte. De Gruyter, Berlin / New York 2005, ISBN 3-11-015714-4 , p. 345 f .; here: p. 345.