Embryology

The embryology ( from Ancient Greek: ἔμβρυον ( Embryo ) " unborn fetus " and -logy ) is that branch of developmental biology that deals with the development of the fertilized egg and the resulting embryo. It also speaks of the prenatal developmental biology.

In medicine and zoology is handled by the embryology as a result the growth of the fetus.

History

From Greek scholars of the 5th and 4th centuries BC, the first theories on the development of the embryo originate. These were influenced by the idea that we are dealing with an act of divine creation. Here, Aristotle assumed that the menstrual blood will activated by sperm and embryonic Initiate. The Greek physician Galen described in his work On the formation of the fetus in the 2nd century AD, the prenatal development and extraembryonic structures such as the placenta. These teachings shaped the embryology to the modern era. First measurements of different stages of embryonic development took Leonardo da Vinci before. This approach was further elaborated by William Harvey, by examining the mid-17th century using simple magnifying lenses chicken embryos. In addition, Harvey explored the development of Damhirschs, in which he could find no early embryonic stages. From this he concluded incorrectly that the uterus secreting the embryos. He was refuted in 1672 by Reinier de Graaf, the small chambers discovered by using the first microscopes in the rabbit uterus. He drew the conclusion that this could not come from the uterus but from other organs, which he named as the ovaries. In these also he discovered the after named him mature ovarian follicles ( Graafian follicle ).

The discovery of a supposedly pre-formed chick in an unfertilized egg by Marcello Malpighi and the discovery of the sperm came up with a counter-thesis to the previous Epigenesetheorie. The representatives of the preformation theory assumed that either the egg or the sperm of the man in a tiny format already vorliege and only had to grow. The preformation established itself and was only in 1759 strongly criticized by Caspar Friedrich Wolff, as this could show that embryos develop from small spherical structures and described by Malpighi embryos in eggs could not find. Wolff was assumed that would arise by division and differentiation of a cell germ layers from which then develop the embryo.

As the founder of modern embryology is true, the German physician Robert Remak. He described 1842, the three germ layers ectoderm, mesoderm and endoderm. He realized before Rudolf Virchow and Theodor Schwann 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.

From the beginning of the 19th century, more and more scientists have focused on the imported Wolff cotyledon term. Here, Étienne Geoffroy Saint- Hilaire justify his son Isidore Saint- Hilaire and Johann Friedrich Meckel the Younger doctrine of developmental disorders by reproductive toxicants ( Teratology ). Christian Heinrich Pander's discovery that there are three different germ layers and Karl Ernst von Baer's discovery of the ovum confirmed the germ layer concept adopted and the underlying Epigenesetheorie.

Stages of development in humans

At the beginning of the development of a person is gametogenesis. A gamete is a formed from primordial germ cell that has a haploid set of chromosomes. Now meets in designing a male Gametenzelle ( sperm ) on a female Gametenzelle ( egg, oocyte ) may occur for fertilization (impregnation ).

The development of the zygote is identified in the first two weeks after fertilization than blastogenesis. Here the embedding ( nidation or implantation ) of the seed takes place (at the 6th or 7th day).

In smooth transition to this is the embryogenesis. It denotes the differentiation of the various cell layers up to the fetus. It begins about the third week pc ( after conception ) and can uA be tied to the formation of the third germ layer. As a result of embryogenesis almost all institutions are created in fundamentals and the Utero - Placental circulation is formed.

From the ninth week of development until birth is now called a fetus instead of an embryo. While growing Fetogenese and differentiate further applied during embryogenesis organs.

Embryology in Islam

There are also religiously based Embryologien. For the Islamic notions of embryogenesis is the following Quranic statement of central importance:

"We have created man from a portion of clay. Then we made him as a drop ( nutfa ) in a tight container ( Qarar Makin ). Then we created the drop a clot ( ʿ alaqa ), this to a lump of flesh ( mudgha ) and this bone. And we clothed the bones with flesh. Then we brought it forth as another creature ( chalaq Achar ). "

After the presentation of Muslim scholars such as Ibn al - Qaiyim Dschauzīya God has summarized the formation and development of the people until the resurrection on the Day of Judgment in these verses. For the interpretation of the Koran passage is a hadith of great importance, which is narrated by ʿ Abd Allāh ibn Mas ʿ ūd. It reads as follows:

"If one of you is created, it will be brought together in his mother's womb for forty days. Then he is there also a ʿ alaqa, then he is there a mudgha, then the angel is sent to him who breathes the soul. And he puts four things fixed: he writes on his ( later ) livelihood, his hour of death, his actions and ' damn ' or ' blessed '. "

Generally, this hadith is interpreted to mean that the three phases of prenatal development ( nutfa, ʿ alaqa, mudgha ) each run in 40 days and then, on the 120th day of pregnancy, the inspiration of man takes place in the mentioned in the Quran transformation "another creature " goes hand in hand. While the movement of the embryo before ensoulment as a result of external influences and organic growth can be limited, it should then be done by the own will of the new man. Until the early 1980s, the doctrine of the inspiration of the embryo was general consensus on the 120th day, but today there is a significant minority of Muslim scholars that interprets the hadith differently and accordingly accepts the inspiration of the embryo after the 40th day. The question of Beseelungszeitpunktes is for the legal assessment of abortion in Islam is of fundamental importance.