What are the main parts of the placenta and when does it fully develop?

The placenta consists of a fetal part called the chorion frondosum and a maternal part called the decidua basalis. It fully develops by the end of the 4th week of pregnancy, establishing a vascular network for exchange.

How do chorionic villi form and what are their types?

Chorionic villi develop in stages: primary villi are cytotrophoblast projections with a syncytiotrophoblast covering; secondary villi have mesoderm in the core; tertiary villi contain fetal blood vessels in the mesoderm.

What is the placental barrier and how does it change during pregnancy?

The placental barrier separates maternal and fetal blood in villi, allowing exchange of gases, nutrients, and wastes. In early pregnancy, it has multiple layers, but by late pregnancy, it thins to only syncytiotrophoblast and fetal capillary endothelium.

How does placental circulation work for the mother and fetus?

Placental circulation involves maternal spiral arteries bringing blood to intervillous spaces, drained by endometrial veins, and fetal umbilical arteries bringing blood to the placenta, with the umbilical vein returning oxygenated blood to the fetus.

What are the key functions of the placenta?

The placenta performs essential functions such as gas exchange, nutrient and waste transfer, maternal antibody transfer, and hormone production.

What are some common congenital anomalies of the placenta?

Common congenital anomalies include shape-related issues like bilobed or diffuse placentas, and umbilical cord attachment anomalies such as marginal (Battledore) or velamentous insertion.

How is the placenta structured into cotyledons?

The placenta is divided into 15–20 cotyledons by septae from the endometrium, with each cotyledon containing 2–3 anchoring villi, forming its discoid shape at full term.

What clinical conditions are associated with placental development?

Clinical conditions include placenta previa, where implantation near the internal os leads to bleeding risks; ectopic pregnancy, with placental development outside the uterus; and chorionic villus biopsy for genetic diagnosis.

Placenta Development – Chorionic Villi & Circulation

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