Which hormones come from the placenta, which from the ovary, and what triggers childbirth in humans?
Riya Singh12th Sample
6 Oct 2026 · 1 min read
I read the pregnancy section of Human Reproduction at midnight and ended up writing half a poem about it, which is not helpful for marks 😂
Serious doubts though. I understand that the placenta is the structural and functional unit between the foetus and the mother, with chorionic villi interdigitated with uterine tissue, and the umbilical cord connects it to the embryo. I also know it makes hormones. My notes have: hCG, hPL, estrogens, progestogens, and then relaxin.
Where do I put relaxin? Is it placental or from somewhere else? And hCG, hPL, relaxin are said to be produced "only during pregnancy" in women, so are they different from the estrogen and progesterone, which are also made in non-pregnant women?
Then parturition. NCERT talks about a "foetal ejection reflex" and oxytocin. I can't connect them. Who sends the signal first, mother or baby? And colostrum: what's special about it?
I would like to write one clear paragraph for each, instead of one messy poem.
8 answers & replies
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[+][–]Nisha Verma12thSample· 13d ago
Placenta = exchange site. Oxygen and nutrients go from mother to foetus; CO2 and excretory waste go from foetus to mother. The cord carries these to and from the embryo. As an endocrine tissue it makes hCG, hPL, estrogens and progestogens. hCG and hPL (and relaxin) are made only in women during pregnancy. Estrogens and progesterone are present all the time in women, but their levels shoot up during pregnancy. Relaxin is separate, see below.
[+][–]Pooja Iyer12thSample· 13d ago
the hormone list for the exam:
- placenta: hCG, hPL, estrogen, progesterone
- ovary: relaxin (in the later phase of pregnancy), and oxytocin comes from the placenta to cause labour contractions
- others go up too: cortisol, prolactin, thyroxine
basically the mother's whole system is amplified!
[+][–]Siddharth RaoDropperSample· 13d ago
Pooja, there's a wrong item in your list. Oxytocin is not from the placenta. It comes from the maternal pituitary (posterior lobe), it's released in response to the signal from the foetus and placenta. Relaxin is correctly from the ovary (later phase of pregnancy). I would remove oxytocin from the placenta line, or an assertion-reason question will catch you.
[+][–]Pooja Iyer12thSample· 13d ago
oh no, yes. I confused oxytocin with hCG since both come in "labour and pregnancy" chapters, my bad. Fixed in my notes!!
[+][–]Tanvi Deshmukh12thSample· 13d ago
Parturition story in order!! 🙂
- Signal comes from the fully developed foetus and placenta → mild uterine contractions = foetal ejection reflex.
- This triggers the mother's pituitary to release oxytocin.
- Oxytocin acts on uterine muscle → stronger contractions.
- Stronger contractions → more oxytocin release. That 3 → 4 → 3 loop is a positive feedback cycle, and it keeps building until the baby is expelled. After that the placenta is also expelled.
[+][–]Riya Singh12thSample· 13d agoAuthor
thank you, now I can write one clean paragraph. the loop even has a rhythm to it, which is probably why I wrote a poem 🙂
[+][–]Zoya Khan12thSample· 13d ago
Colostrum is the milk produced in the first few days of lactation. It contains several antibodies, which are important for developing the newborn's resistance. The mammary glands differentiate during pregnancy and lactation starts after birth, which is why NCERT places it right after parturition. For the exam: "milk in first few days" + "antibodies" = colostrum.
[+][–]Ishita GoyalDropperSample· 13d ago
Also the mini timeline that NCERT gives, in case the paper asks for an order: heart is formed after 1 month; limbs and digits by the end of the 2nd month; most major organ systems by the end of 12 weeks (first trimester); first movements of the foetus and hair on the head around the 5th month; by the end of 24 weeks the body has fine hair, eyelids separate and eyelashes form; and at about 9 months the foetus is fully developed. Not a ton to learn.
