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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 ...
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]
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.
The respiratory system develops from the lung bud, which appears in the ventral wall of the foregut about four weeks into development. The lung bud forms the trachea and two lateral growths known as the bronchial buds, which enlarge at the beginning of the fifth week to form the left and right main bronchi .
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.
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]
Image showing trophoblast differentiated into the two layers of cytotrophoblast and syncytiotrophoblast during implantation. It is the outer layer of the trophoblasts and actively invades the uterine wall, during implantation, rupturing maternal capillaries and thus establishing an interface between maternal blood and embryonic extracellular fluid, facilitating passive exchange of material ...
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.