Placenta
நஞ்சுக்கொடி
The placenta is not just a barrier; it is an endocrine powerhouse. If you think it only supplies nutrients, you are losing marks. It is the bridge that dictates fetal survival.
The idea
The placenta is the structural and functional unit between the developing embryo and the maternal body. It facilitates the supply of oxygen and nutrients to the embryo and the removal of carbon dioxide and excretory waste materials produced by the embryo. It is connected to the embryo through the umbilical cord, which helps in the transport of substances to and from the embryo.
Why it matters
It acts as a life-support system for the fetus, providing nutrition, gas exchange, and endocrine functions during gestation.
NEET lens
NEET focuses on the hormones secreted by the placenta. Memorize that hCG, hPL, and relaxin are produced only during pregnancy. Do not confuse the placenta's endocrine function with the ovary's role. Expect questions on the specific list of hormones secreted during the later stages of pregnancy.
Clinical significance
Placental failure leads to intrauterine growth restriction (IUGR) or fetal hypoxia. Furthermore, the placenta acts as an endocrine tissue, secreting hCG, hPL, estrogens, and progestogens, which are essential for maintaining pregnancy. Failure to secrete these hormones results in spontaneous abortion.
Introduction
The placenta is a temporary, disc-shaped organ formed during pregnancy from both fetal (trophoblast) and maternal (decidua basalis) tissue, serving as the site of exchange of nutrients, gases, and waste between fetal and maternal blood without direct mixing of blood.
Core concept
Development: implanted blastocyst → trophoblast → cytotrophoblast + syncytiotrophoblast → placental villi develop → interdigitate with maternal decidua basalis → uteroplacental circulation established by Week 10. Structure: chorionic villi (fetal, bathed in maternal blood in intervillous space). Fetal blood in villi; maternal blood in space — NO direct mixing. Functions: (1) Nutrition: glucose, amino acids, fatty acids, vitamins. (2) Gas exchange: O₂ to fetus, CO₂ from fetus. (3) Waste removal: urea, bilirubin to maternal blood. (4) Hormone production: hCG (maintains corpus luteum in early pregnancy), hPL (human placental lactogen), estrogen, progesterone (takes over from corpus luteum by Week 10). (5) Immunological: IgG antibodies cross to fetus (passive immunity). Barrier function: partial — drugs, viruses (HIV, rubella), alcohol cross placenta.
Go deeper
hCG (human chorionic gonadotropin): produced by syncytiotrophoblast from Day 8 after fertilization. Peak at Week 10-12 → falls. Maintains corpus luteum (→ progesterone → prevents menstruation). Detected in urine by pregnancy tests from Day 10-14. Basis of all pregnancy tests (immunoassay for hCG).
From Class 10
During pregnancy, the developing baby gets oxygen and nutrients from the mother through the placenta — a temporary organ that connects mother and baby.