On this page
Parturition and lactation take less than a page of NCERT, but questions on them mix hormones from two chapters: human reproduction and chemical coordination. Students lose marks by swapping prolactin and oxytocin, or by forgetting where oxytocin is actually made. This post builds one timeline from pregnancy to feeding and reads some real numbers on colostrum.
Where is this in the syllabus?
The NEET (UG) 2026 syllabus lists "Parturition (Elementary idea); Lactation (Elementary idea)" under human reproduction, and the CBSE 2026-27 Class XII Biology curriculum uses the same wording. The text is section 2.7 of the NCERT Class 12 chapter, Human Reproduction, with the hormone sources in the NCERT Class 11 chapter on chemical coordination. Both are 2026-27 reprints. Check the syllabus for your exam year.
Which hormones does pregnancy add?
NCERT says the placenta acts as an endocrine tissue, producing human chorionic gonadotropin (hCG), human placental lactogen (hPL), estrogens and progestogens. Late in pregnancy the ovary also secretes relaxin. Remember the set NCERT singles out: hCG, hPL and relaxin are produced only during pregnancy. Estrogens, progestogens, cortisol, prolactin and thyroxine rise several-fold in the mother's blood.
How does parturition start, and why does it keep going?
NCERT gives the average gestation as about 9 months. Then:
Signals from the fully developed foetus and the placenta cause mild uterine contractions, the foetal ejection reflex.
This triggers oxytocin release from the maternal pituitary.
Oxytocin acts on uterine muscle and causes stronger contractions.
Stronger contractions stimulate more oxytocin, and the cycle repeats until the baby is expelled. The placenta follows soon after.
This is positive feedback: the output strengthens the input, so the process runs to completion rather than settling. Our post on hormones and feedback loops contrasts it with the negative feedback of the thyroid axis.
The Class 11 chapter adds a detail students miss: oxytocin is synthesised in the hypothalamus, carried along axons, and stored and released by the posterior pituitary. NCERT ends the section asking what doctors inject to induce delivery; the chapter's own logic points to the hormone that strengthens contractions.
Prolactin makes milk; oxytocin moves it
NCERT Class 11 states that prolactin (anterior pituitary) regulates growth of the mammary glands and formation of milk, and that oxytocin stimulates milk ejection. Keep the verbs apart: prolactin makes, oxytocin ejects.
OpenStax Anatomy and Physiology 2e explains the timing. Prolactin rises through pregnancy to about 10 to 20 times its pre-pregnancy level, but placental estrogen and progesterone hold back milk synthesis until the placenta is expelled. When the infant suckles, the posterior pituitary releases oxytocin, and milk is let down in under a minute. That let-down reflex is a second positive feedback loop.
Worked example: reading the colostrum numbers
NCERT says colostrum, the milk of the first few days, contains antibodies that help the newborn develop resistance. OpenStax gives a composition table, in grams per litre, that shows how strong the difference is.
Immunoglobulins: colostrum 19, mature milk 0.1. Ratio 19 / 0.1 = 190 times more in colostrum.
Total protein: 23 against 11. Ratio 23 / 11 ≈ 2.1 times.
Fat: 30 against 45. Colostrum has 30 / 45 = two-thirds the fat of mature milk.
Lactose: 57 against 71, about 0.80 times.
So colostrum is a small-volume, antibody-dense first feed rather than an energy-rich one. OpenStax adds that it is secreted for the first 48 to 72 hours. This is why the WHO and UNICEF recommendation starts early: begin breastfeeding within 1 hour of birth, breastfeed exclusively for the first 6 months, then continue to 2 years or beyond alongside other foods. For any personal health question about pregnancy or feeding, a doctor is the right person to ask.
Which mistakes cost marks?
Oxytocin made in the posterior pituitary. It is made in the hypothalamus and released there.
Prolactin causing milk ejection. Prolactin forms milk; oxytocin ejects it.
Calling parturition negative feedback. It is positive feedback.
Relaxin from the placenta. NCERT says the ovary.
Colostrum as "first milk with more fat". It has more antibodies and protein, less fat.
A practice routine
Draw the parturition loop as four boxes in a circle, then the let-down loop beside it.
Make a three-column list: hormone, where made, job. Include hCG, hPL, relaxin, oxytocin and prolactin.
Redo the colostrum ratios for protein and fat without looking.
Link this to the cycle and gametogenesis in our human reproduction guide.
If hormone names keep sliding together, the Fermi Concept Library has every concept in biology with its own lesson, so you can revise the pituitary on its own before returning to this chapter.
Tonight, write the hormone, source and job list from memory and check it against both NCERT chapters.
