Human Reproduction
1. Introduction
Human reproduction involves complex physiological processes from gamete formation through childbirth. This chapter covers the reproductive system, gametogenesis, and reproductive health.
2. Male Reproductive System
2.1 Organs
Testes: Paired, situated in scrotum (temperature 2-3°C below body temperature). Produce sperm and testosterone. Epididymis: Storage and maturation of sperm. Vas deferens: Transports sperm during ejaculation. Seminal vesicles, Prostate, Bulbourethral glands: Accessory glands. Secrete seminal fluid (alkaline, nutrient-rich).
2.2 Structure of Sperm
Head (acrosome + nucleus), middle piece (mitochondria for energy), tail (flagellum for motility).
3. Female Reproductive System
3.1 Organs
Ovaries: Paired. Produce ova and hormones (oestrogen, progesterone). Fallopian tubes (oviducts): Site of fertilisation. Fimbriae collect the ovum. Uterus: Implantation and foetal development. Cervix: Lower part of uterus, connects to vagina.
3.2 Structure of Ovum
Non-motile, large, surrounded by zona pellucida and corona radiata.
4. Gametogenesis
4.1 Spermatogenesis (in Seminiferous Tubules)
Spermatogonia (2n) → Primary spermatocyte (2n) → Secondary spermatocyte (n) → Spermatids (n) → Spermatozoa (n).
Hormonal control: GnRH → FSH (acts on Sertoli cells) + LH (acts on Leydig cells → testosterone).
4.2 Oogenesis (in Ovaries)
Oogonia (2n) → Primary oocyte (2n) → Secondary oocyte (n) + First polar body → Ovum (n) + Second polar body.
Oogenesis starts before birth but is arrested at prophase I until puberty. Each menstrual cycle completes one oocyte.
5. Menstrual Cycle
Duration: ~28 days.
Menstrual phase (Days 1-5): Breakdown of endometrium, bleeding. Follicular phase (Days 5-13): Follicle development, oestrogen rises. Ovulation (Day 14): LH surge triggers ovum release. Luteal phase (Days 15-28): Corpus luteum secretes progesterone. If no fertilisation, corpus luteum degenerates.
6. Fertilisation, Pregnancy, Parturition
Fertilisation: In ampulla of fallopian tube. Sperm penetrates zona pellucida, acrosome reaction.
Implantation: Blastocyst embeds in uterine wall (~day 7).
Gestation: ~9 months (40 weeks). Human chorionic gonadotropin (hCG) maintains pregnancy.
Parturition: Childbirth. Oxytocin stimulates uterine contractions.
7. Reproductive Health
7.1 Contraception
Natural: Rhythm method, coitus interruptus. Barrier: Condoms, diaphragm, cervical cap. IUDs: Copper-T (Cu ions act as spermicide). Hormonal: Pills (oestrogen + progesterone inhibit ovulation). Surgical: Vasectomy (male), Tubectomy (female).
7.2 STIs (Sexually Transmitted Infections)
Bacterial: Gonorrhoea, Syphilis, Chlamydia. Viral: HIV, Herpes, HPV. Treatment: Bacterial STIs are curable with antibiotics. Viral STIs can be managed but not always cured.
7.3 Infertility
Assisted Reproductive Technologies (ART):
- IVF (fertilisation outside body).
- ICSI (sperm injected directly into egg).
- GIFT, ZIFT (gamete/zygote intrafallopian transfer).
- Surrogacy.
8. Worked Problems
Problem 1: Trace the path of sperm from its production to ejaculation. Solution: Seminiferous tubules → Epididymis → Vas deferens → Ejaculatory duct → Urethra → Penis.
9. Common Mistakes
'Students often think testosterone is produced by the seminiferous tubules. It is actually produced by the Leydig cells in the interstitial tissue between tubules.'
10. ISC Exam Focus
| Topic | Theory Marks | Practical Marks |
|---|---|---|
| Male and female systems | 3 | 2 |
| Gametogenesis | 4 | 2 |
| Menstrual cycle | 3 | 2 |
| Contraception and health | 3 | 1 |
11. Self-Test Questions
- Draw a labelled diagram of the male reproductive system and describe each part.
- Explain the process of spermatogenesis under hormonal control.
- Describe the phases of the menstrual cycle with the associated hormonal changes.
- What are STIs? Name three bacterial and three viral STIs.
- Explain the principle of IVF and mention its applications.
