Human Reproduction

🟢 Lite — Quick Review (1h–1d)

Rapid summary for last-minute revision before your exam.

Human Reproduction — Quick Facts

Human reproduction is sexual, requiring both male and female gametes (sperm and ovum) which fuse via fertilisation to form a zygote.

Male Reproductive System:

• Testes: Paired organs in the scrotum (temperature 2–3°C below body — essential for spermatogenesis). Each testis has ~250 m coiled seminiferous tubules where sperm are produced. Leydig cells between tubules produce testosterone.
• Epididymis: Site of sperm maturation and storage (capacitation begins here)
• Vas deferens: Transports sperm from epididymis to urethra
• Prostate gland: Secretes alkaline fluid containing citric acid, acid phosphatase, prostaglandins (~30% of semen volume)
• Seminal vesicles: Paired glands; secrete fructose-rich fluid (~60% of semen; provides energy for sperm)
• Penis: Contains erectile tissue (corpus cavernosum and corpus spongiosum)

Female Reproductive System:

• Ovaries: Paired organs; each contains ~2 million primordial follicles at birth. Only ~300–400 mature and ovulate during reproductive lifetime. Produce oestrogen and progesterone.
• Fallopian tubes (Oviducts): Ciliated epithelium; site of fertilisation (ampullary-isthmic junction)
• Uterus: Pear-shaped muscular organ; endometrium (inner lining) proliferates and shed in menstruation
• Vagina: Muscular tube; receives penis during copulation

Gametes:

• Sperm: Head (nucleus + acrosome cap containing hyaluronidase for egg penetration), midpiece (mitochondria for energy), tail (flagellum)
• Ovum: Largest cell in human body (100–120 μm diameter); surrounded by zona pellucida (ZP1, ZP2, ZP3 glycoproteins); corona radiata (layer of follicular cells)

⚡ Exam tip: Capacitation is the final maturation of sperm — occurs in female reproductive tract over 5–7 hours. It removes cholesterol from the sperm membrane and increases membrane fluidity, enabling the acrosome reaction to occur.

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🟡 Standard — Regular Study (2d–2mo)

Standard content for students with a few days to months.

Human Reproduction — NEET/JEE Study Guide

Menstrual Cycle (28-day cycle, controlled by FSH and LH):

Phase	Days	Key Events	Hormones
Menstrual	1–5	Endometrium shed (bleeding)	FSH rising, LH low, progesterone low
Proliferative/Follicular	6–14	Endometrium regenerates, follicle matures	FSH stimulates follicle → oestrogen rises
Ovulatory	Day 14	LH surge triggers ovulation (Follicle ruptures)	LH surge (peak), oestrogen peak
Secretory/Luteal	15–28	Endometrium prepares for implantation	Progesterone high, oestrogen high

If fertilisation does not occur → corpus luteum degenerates → progesterone drops → menstruation begins.

Ovulation: Triggered by LH surge (mid-cycle, ~36 hours before ovulation). FSH also peaks at this time. The mature Graafian follicle (18–20 mm) ruptures, releasing the ovum. The LH surge is the basis of ovulation predictor kits.

Fertilisation:

1. Sperm capacitation (5–7 hours in female tract)
2. Sperm penetrates corona radiata ( hyaluronidase)
3. Acrosome reaction: releases enzymes to penetrate zona pellucida (ZP3 is the primary sperm receptor)
4. Sperm fuses with egg membrane
5. Zona reaction: zona pellucida hardens (prevents polyspermy)
6. Second meiotic division of secondary oocyte completes
7. Male and female pronuclei form → fuse → zygote

Twins:

• Monozygotic (identical): Single zygote splits → same sex, identical genetics. ~0.4% of births.
• Dizygotic (fraternal): Two separate ova fertilised by two sperm → no more similar than siblings. Increased with maternal age and fertility drugs.

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🔴 Extended — Deep Study (3mo+)

Comprehensive coverage for students on a longer study timeline.

Human Reproduction — Comprehensive Notes

Spermatogenesis (continuous process in males):

Spermatogonium (2n) → Primary spermatocyte (2n, meiosis I) → Secondary spermatocytes (n, meiosis II) → Spermatids (n) → Spermatozoa (n, spermiogenesis) → Capacitated sperm

Each primary spermatocyte produces 4 sperm. Spermatogenesis takes ~74 days. The process is stimulated by testosterone (from Leydig cells) and inhibin (from Sertoli cells, regulates FSH).

Sertoli Cells (Nurse Cells):

• Provide nutrition to developing sperm
• Secrete inhibin (inhibits FSH)
• Secrete androgen-binding protein (ABP) — maintains high testosterone concentration in seminiferous tubules
• Form blood-testis barrier (tight junctions between Sertoli cells) to protect haploid germ cells from immune attack

Oogenesis (process in females):

• At birth: ~2 million primary oocytes arrested in Prophase I of meiosis
• Each month (from puberty): One primary oocyte resumes meiosis I → secondary oocyte (arrests at Metaphase II, stays arrested until fertilisation)
• If fertilised: Secondary oocyte completes meiosis II → ovum + second polar body
• If not fertilised: Secondary oocyte degenerates within 24 hours of ovulation

Pregnancy (Gestation):

• Cleavage divisions: Zygote → 2-cell → 4-cell → 8-cell → morula (16 cells) → blastocyst (by day 5)
• Blastocyst: Inner cell mass (becomes embryo) + trophoblast (becomes placenta) + blastocoel
• Implantation: ~6–7 days post-fertilisation; blastocyst embeds in endometrium
• Placenta forms by week 12; produces hCG (human chorionic gonadotropin) — the basis of pregnancy tests
• hCG maintains corpus luteum (which produces progesterone) until placenta takes over (~8–10 weeks)

Critical Periods of Pregnancy:

• First trimester (weeks 1–12): Organogenesis — most vulnerable to teratogens (thalidomide caused phocomelia, rubella caused deafness and cataracts)
• Second trimester: Rapid growth, differentiation
• Third trimester: Lung maturation (surfactant production by week 34)

Contraception Methods:

Method	Mechanism
Condom (male)	Physical barrier; also prevents STI
Oral contraceptive pills	Suppress ovulation (oestrogen + progestin or progestin-only)
Copper-T (IUD)	Copper ions are spermicidal; prevents implantation
Emergency contraception	Levonorgestrel (up to 72h) — inhibits ovulation/fertilisation
Surgical sterilisation	Vasectomy (male) / tubectomy (female) — permanent
Rhythm method	Abstaining from intercourse during fertile window (unreliable)

NEET Pattern Analysis: Human reproduction contributes 2 questions per year. High-yield areas: menstrual cycle phases and hormones, spermatogenesis vs oogenesis, fertilisation steps, placental function, and contraceptive methods. The LH surge and hormonal changes in menstrual cycle are frequently combined questions.

⚡ NEET 2022 Qn: Which hormone is detected by pregnancy test kits? Answer: hCG (human chorionic gonadotropin) — produced by the trophoblast cells of the blastocyst and later by the placenta.