- The placenta is a temporary fetomaternal organ that develops during pregnancy and facilitates exchange of nutrients, gases, and waste between the mother and the fetus.
- It also serves as an endocrine organ, producing essential hormones to maintain pregnancy.
Development of Placenta
1. Formation of Chorionic Villi:
- Begins at Day 13–15 post-fertilization.
- Trophoblast differentiates into cytotrophoblast (inner layer) and syncytiotrophoblast (outer layer).
- Lacunae appear within the syncytiotrophoblast, forming the intervillous space.
2. Primary Villi (Day 13):
- Solid columns of cytotrophoblast surrounded by syncytiotrophoblast.
3. Secondary Villi (Day 16):
- Extraembryonic mesoderm invades the core of primary villi.
4. Tertiary Villi (Day 21):
- Blood vessels form inside the mesodermal core, establishing fetomaternal circulation.
Structure of the Placenta
- Maternal Component: Decidua Basalis
- Fetal Component: Chorion Frondosum
- The placenta is discoid in shape, measuring 15-20 cm in diameter, 2-3 cm thick, and weighs 500-600 g at term.
Circulation in the Placenta
Maternal Circulation (Uteroplacental Circulation)
- Spiral arteries in the uterus open into intervillous spaces, supplying maternal blood.
- Exchange of gases, nutrients, and waste products occurs between maternal and fetal blood.
Fetal Circulation (Fetoplacental Circulation)
- Two umbilical arteries carry deoxygenated blood from the fetus to the placenta.
- One umbilical vein carries oxygenated blood from the placenta to the fetus.
Functions of the Placenta
1. Respiratory Function
- Oxygen from maternal blood diffuses into fetal blood.
- COâ‚‚ is removed from fetal blood into maternal circulation.
2. Nutritional Function
- Glucose, amino acids, fatty acids, and vitamins cross from mother to fetus.
3. Excretory Function
- Waste products like urea, uric acid, and bilirubin are transferred from fetal to maternal blood.
4. Endocrine Function
- Human Chorionic Gonadotropin (hCG): Maintains corpus luteum.
- Progesterone: Maintains uterine lining.
- Estrogen: Promotes fetal growth and maternal changes.
- Human Placental Lactogen (hPL): Modulates maternal metabolism.
5. Immunological Function
- Transfers maternal antibodies (IgG) to provide passive immunity.
Placental Changes at Term
- Syncytial Knots: Aggregations of syncytiotrophoblast nuclei.
- Degeneration of Villi: Reduced number of functional villi.
- Fibrinoid Deposition: Accumulation of fibrinoid material.
- Calcification: Deposits of calcium appear.
Abnormalities of the Placenta
- Placenta Previa – Placenta implanted near or covering the cervix.
- Placental Abruption – Premature separation of the placenta.
- Placenta Accreta/Increta/Percreta – Abnormal adherence of placenta to the uterine wall.
- Succenturiate Placenta – Extra lobes of placental tissue.
- Circumvallate Placenta – Thickened ring at the margin of the placenta.
