Blastocyst with an inner cell mass and trophoblast.
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| colspan="2" |Blastodermic vesicle of Vespertilio murinus.
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|Latin
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|colspan="2"|[subject #6 ]
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|System
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|Precursor
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|MeSH
|colspan="2"|[A16.254.085.162]
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|Dorlands/Elsevier
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The trophoblast (from Greekthrephein: to feed) is considered to be the first of all embryonic annexes. It secretes hCG in order to maintain progesterone secretion and sustain a pregnancy. Trophoblasts are invasive, eroding, and metastasizing cells of the placenta. They are formed during the first stage of pregnancy and are the first cells to differentiate from the fertilized egg.
The invasion of a specific type of trophoblast (extravillous trophoblast) into the maternal uterus is a vital stage in the establishment of pregnancy. Failure of the trophoblast to invade sufficiently may be important in the development of some cases of pre-eclampsia, while too firm an attachment may lead to placenta accreta.
Trophoblasts mediate the implantation of the fetus into the placenta, but they are never incorporated into the mother's body or the fetus. They are not "fetal" cells.
Trophoblasts become inert during pregnancy and are completely rejected by the fetus and mother at delivery. They can be seen as the thin membrane covering the fetus at birth, the caul.
