Placenta: Structure, Functions and the Umbilical Cord
Biology · Human Reproduction · NEET
The placenta is a disc-shaped organ made when finger-like chorionic villi from the embryo interlock with the mother's uterine tissue and maternal blood. It supplies oxygen and food to the foetus, removes waste, and also acts as an endocrine gland making hormones like hCG, hPL, estrogen, progesterone and relaxin. Memory hook: think "PLACENTA = the baby's Post office" (Passes food/O2 in, Picks up waste, Produces hormones), and the umbilical cord is the delivery road.
The placenta forms where foetal chorionic villi interlock with the mother's uterine tissue and maternal blood. The two blood supplies stay separate (placental barrier), but oxygen, food, carbon dioxide and waste cross it, and the placenta also releases hormones. The umbilical cord links the placenta to the embryo.
Your doubts, answered
Is the placenta made from the embryo or from the mother?
It is made from BOTH. Finger-like chorionic villi grow out from the trophoblast of the embryo, and these interdigitate (interlock) with the uterine tissue and maternal blood of the mother. So the placenta is a shared structural and functional unit between the foetus and the mother. NEET loves this 'joint' wording.
Do the mother's blood and the baby's blood mix in the placenta?
No. The chorionic villi are bathed in maternal blood, but the two blood supplies stay separate, divided by the placental barrier. Only gases, nutrients and wastes pass across by diffusion. This is exactly why, in Rh incompatibility, the foetal Rh+ blood does not normally reach the Rh- mother in the first pregnancy.
What is the exact function of the umbilical cord?
The umbilical cord connects the placenta to the embryo and helps in the transport of substances to and from the embryo. Simply: it is the pipe carrying food and oxygen toward the foetus and carrying waste back toward the placenta. Do not confuse it with the placenta itself, which is the exchange organ.
Why is the placenta called an endocrine tissue or endocrine gland?
Because after implantation it also secretes hormones directly into the blood. NCERT lists human chorionic gonadotropin (hCG), human placental lactogen (hPL), estrogens and progestogens; relaxin is also produced in later pregnancy. Since it makes hormones without a duct, it acts as a temporary endocrine gland during pregnancy.
What does the placenta actually do for the growing baby?
Four jobs: (1) supplies oxygen to the foetus, (2) supplies nutrients (food), (3) removes carbon dioxide and excretory/waste materials, and (4) secretes hormones that maintain pregnancy. It is the foetus's lung, gut, kidney and gland all in one.
⚠️ The NEET trap ✗ hCG is secreted by the ovary because the ovary makes the pregnancy hormones. ✓ hCG (and hPL, estrogens, progestogens) are secreted by the PLACENTA, which acts as an endocrine tissue after implantation. The ovary's corpus luteum makes progesterone, but hCG is a placental product. 🧠 When a NEET option pairs 'Placenta' with 'hCG', that match is correct (NEET 2020 match-column: Placenta - hCG). Do not swap it to the ovary.
Real NEET questions
2016
Several hormones like hCG, hPL, estrogen, progesterone are produced by:
A · Ovary
B · Placenta ✓
C · Fallopian tube
D · Pituitary
Solution: After implantation the placenta acts as an endocrine tissue and secretes hCG, human placental lactogen (hPL), estrogens and progestogens. These are placental products, not ovarian, tubal or pituitary secretions. NCERT Ch 2: 'Placenta also acts as an endocrine tissue and produces several hormones.'
2020
Match Column-I with Column-II: (a) Placenta (b) Zona pellucida (c) Bulbourethral glands (d) Leydig cells; (i) Androgens (ii) Human Chorionic Gonadotropin (hCG) (iii) Layer of the ovum (iv) Lubrication of the penis
A · a-iii, b-ii, c-iv, d-i
B · a-ii, b-iii, c-iv, d-i ✓
C · a-iv, b-iii, c-i, d-ii
D · a-i, b-iv, c-ii, d-iii
Solution: Placenta produces hCG (a-ii); zona pellucida is a layer of the ovum (b-iii); bulbourethral gland secretion lubricates the penis (c-iv); Leydig cells secrete androgens (d-i). So a-ii, b-iii, c-iv, d-i, which is option B.
Solved Human Reproduction NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It begins forming after implantation of the blastocyst, when chorionic villi appear on the trophoblast and interlock with the uterine tissue. It then serves the foetus through pregnancy.
What is the placental barrier?
It is the thin partition of chorionic villi and tissue that keeps the maternal blood and foetal blood separate while still allowing exchange of gases, nutrients and wastes by diffusion.
Which hormones does the placenta secrete?
NCERT lists hCG, hPL (human placental lactogen), estrogens and progestogens; relaxin is also secreted in later pregnancy. LH is NOT a placental hormone (it is from the pituitary).
What is the difference between the placenta and the umbilical cord?
The placenta is the disc-shaped exchange organ between foetus and mother. The umbilical cord is the connecting tube that links the placenta to the embryo and transports substances to and from the embryo.
Is the placenta a foetal or maternal organ?
It is both. It is a joint structural and functional unit formed from the foetal chorionic villi plus maternal uterine tissue, so it belongs to neither side alone.
