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The chorionic villi are at first small and non-vascular. 13–15 days: trophoblast only [1] Secondary: The villi increase in size and ramify, while the mesoderm grows into them. 16–21 days: trophoblast and mesoderm [1] Tertiary: Branches of the umbilical artery and umbilical vein grow into the mesoderm, and in this way the chorionic villi are ...
Placenta with attached fetal membranes (ruptured at the margin at the left in the image), which consists of the chorion (outer layer) and amnion (inner layer).. The part of the chorion that is in contact with the decidua capsularis undergoes atrophy, so that by the fourth month scarcely a trace of the villi is left.
Identical twins have identical genomes in the immediate aftermath of twinning. About two-thirds of monozygotic twins share the same placenta, arising by cleavage before the fourth day of development; the other third have separate placentas because cleavage has taken place after the fourth day after choriogenesis has begun.
The chorionic membrane is a fibrous tissue layer containing the fetal blood vessels. [4] Chorionic villi form on the outer surface of the chorion, which maximise surface area for contact with maternal blood. [4] The chorionic villi are involved in fetal-maternal exchange. [10]
Eventually, the syncytiotrophoblast comes into contact with maternal blood and forms chorionic villi – the beginning of placentation. Following invasion, the breach in the uterine epithelium made by the blastocyst's entry is sealed by a fibrin plug. The fibrin plug is a coagulation of a blood clot and cellular debris. [11]
In humans, the placenta develops in the following manner. Chorionic villi (from the embryo) on the embryonic pole grow, forming chorion frondosum. Villi on the opposite side (abembryonic pole) degenerate and form the chorion laeve (or chorionic laevae), a smooth surface. The endometrium (from the mother) over the chorion frondosum (this part of ...
Chorionic villi (right of image) and cartilage, i.e. fetal parts (left of image). H&E stain. Products of conception, abbreviated POC, is a medical term used for the tissue derived from the union of an egg and a sperm. It encompasses anembryonic gestation (blighted ovum) which does not have a viable embryo.
Histopathology of acute subchorionic intervillositis, with neutrophils in Langhan’s layer of fibrinoid (by the fetal surface, at the base of a chorionic villus, seen at top right). Placentitis is an inflammation of the placenta. The main forms of placentitis are: Villitis, inflammation of chorionic villi.