Introduction
The placenta is an essential organ that develops during pregnancy, serving as the vital link between the fetus and the maternal uterine wall. It facilitates the exchange of gases, nutrients, and waste products between mother and fetus, and performs multiple other functions crucial for fetal development and maternal health.
Formation and Location:
- The placenta forms when the blastocyst implants into the uterine endometrium.
- The trophoblast (outer layer of the blastocyst) differentiates into cytotrophoblast and syncytiotrophoblast layers, creating a barrier between maternal and fetal blood.
- Typically attaches to the upper uterine wall, but can have abnormal placements like placenta previa (low placement) or placenta accreta (abnormal attachment).
Structure:
- Two main parts:
- Fetal portion: Comprised of the chorionic plate covered by the amnion.
- Maternal portion: Bordered by the decidua basalis.
- Decidual septa form between the 4th and 5th months, dividing the placenta into cotyledons (distinct lobes).
- The junctional zone is rich in extracellular matrix, containing trophoblasts and decidual cells for nutrient exchange.
- Full-Term Placenta:
- Shape: Discoid.
- Size: Typically 15-20 cm in diameter, 2-3 cm in thickness, weighing 500-600 grams.
- Surface: Covered with villi (finger-like projections) to increase surface area for nutrient and gas exchange.
- Fetal side is smooth; maternal side is rough due to cotyledons.