By Dr Hemant Upadhyay, Zoology faculty at Pramana Institute (18 years teaching NEET, ex-Allen)
Human reproduction gave about six NEET questions in 2025 by published analyses, and it is a favourite in the Class 12 boards. The questions test exact NCERT facts: which cell secretes what, which hormone peaks when, and what happens on which day. Revise these points twice before every test.
Reproductive systems
- The testes sit in the scrotum, which keeps them 2–2.5 °C below body temperature, as sperm production needs.
- Each testis has about 250 testicular lobules, each with 1–3 seminiferous tubules.
- Sertoli cells in the tubules nourish developing sperm. Leydig (interstitial) cells between the tubules secrete androgens.
- Male duct sequence: rete testis → vasa efferentia → epididymis → vas deferens → ejaculatory duct → urethra.
- Male accessory glands: paired seminal vesicles, one prostate and paired bulbourethral glands.
- The oviduct has three parts: infundibulum (with fimbriae), ampulla and isthmus. The uterine wall has three layers: perimetrium, myometrium and endometrium.
Gametogenesis
| Spermatogenesis | Oogenesis |
|---|---|
| Starts at puberty | Starts before birth, in the fetus; no new oogonia form after birth |
| Spermatogonium (2n) → primary spermatocyte (2n) → secondary spermatocytes (n) → spermatids (n) → sperm | Primary oocyte (arrested in prophase I) → secondary oocyte + first polar body → ovum + second polar body |
| One primary spermatocyte gives 4 sperm | One primary oocyte gives 1 ovum |
| Spermatids become sperm by spermiogenesis; release from the tubule is spermiation | The secondary oocyte is released at ovulation; meiosis II finishes only when a sperm enters |
Hormones: GnRH from the hypothalamus raises LH and FSH. LH acts on Leydig cells to release androgens; FSH acts on Sertoli cells.
Sperm facts: a sperm has a head (acrosome and nucleus), neck, middle piece (mitochondria for energy) and tail. A human ejaculate holds 200–300 million sperm; for normal fertility at least 60% should have normal shape and at least 40% should show vigorous motility.
Menstrual cycle (about 28 days)
| Phase | Days (approx.) | What happens |
|---|---|---|
| Menstrual | 3–5 | Endometrium breaks down and is shed, because the egg was not fertilised |
| Follicular (proliferative) | to about day 14 | Follicles grow under FSH and LH; oestrogen rebuilds the endometrium |
| Ovulation | about day 14 | The LH surge releases the secondary oocyte |
| Luteal (secretory) | day 15–28 | The corpus luteum secretes progesterone, which keeps the endometrium ready for implantation |
The first cycle at puberty is menarche; cycles stop at menopause, around 50 years.
Fertilisation to birth
- Fertilisation happens in the ampullary region of the oviduct. Once a sperm touches the zona pellucida, changes in it block entry of more sperm.
- The sex of the baby is decided by the sperm: an X-carrying sperm gives a girl, a Y-carrying sperm a boy.
- Cleavage gives a morula (8–16 cells), then a blastocyst with an outer trophoblast and an inner cell mass. The trophoblast attaches to the endometrium (implantation), and the inner cell mass becomes the embryo.
- The placenta forms from chorionic villi and uterine tissue. It secretes hCG, hPL, oestrogens and progestogens. Later in pregnancy, the ovary secretes relaxin. hCG, hPL and relaxin are made only in pregnancy.
- Milestones: heart forms after about one month; limbs and digits by the end of the second month; most organ systems by 12 weeks; first movements in the fifth month; eyelids separate and eyelashes form by 24 weeks. Pregnancy lasts about nine months.
- Birth (parturition) is triggered by the fetal ejection reflex, which releases oxytocin. The first milk, colostrum, carries IgA antibodies.
FAQs
Where does fertilisation take place? In the ampullary region of the fallopian tube (oviduct).
Which hormone causes ovulation? The LH surge in the middle of the cycle.
Which cells secrete testosterone? Leydig (interstitial) cells.
Revise NCERT Biology with weekly tests in a batch of at most 40 at Pramana, Geeta Bhawan Square, Indore. See our NEET program and the NEET 90-Day Revision Program.
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