Human Reproduction
Tamil Nadu Board · Class 12 · Zoology
Complete topic list for Human Reproduction in Tamil Nadu Board Class 12 Zoology. Key concepts, sub-topics, and what to focus on for board exams.
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2.1 Human Reproductive System
- The reproductive system has four main functions: produce gametes (sperms and ova), transport and sustain gametes, nurture developing offspring, and produce hormones.
- Primary reproductive organs are testes (in males) and ovaries (in females) — they produce gametes and hormones.
- Testes are located in the scrotum outside the abdominal cavity because viable sperms need a temperature 2–3°C lower than normal body temperature.
2.2 Gametogenesis – Spermatogenesis and Oogenesis
- Gametogenesis = formation of gametes (sperms and ova) from primary sex organs through meiosis.
- Spermatogenesis occurs in seminiferous tubules; produces sperms continuously from puberty throughout life.
- Spermatogonia (2n) → (mitosis + growth) → Primary spermatocytes (2n, 46 chromosomes) → (Meiosis I) → 2 Secondary spermatocytes (n, 23 chromosomes) → (Meiosis II) → 4 Spermatids (n) → (Spermiogenesis)
2.3 Menstrual Cycle
- Menstrual cycle: cyclic changes in the female reproductive system occurring approximately every 28–29 days, from menarche (puberty) to menopause, except during pregnancy.
- Cyclic menstruation is an indicator of normal reproductive phase.
- The menstrual cycle has 4 phases: Menstrual Phase → Follicular Phase → Ovulatory Phase → Luteal Phase.
2.4 Menstrual Disorders and Menstrual Hygiene
- Amenorrhoea = absence of menstruation; Primary amenorrhoea = menarche not appearing by age 18; Secondary amenorrhoea = absence of menstruation for 3+ consecutive months.
- Polymenorrhoea = menstrual cycle shorter than 21 days; due to hyperactive anterior pituitary, psychological disturbances, malnutrition or STDs like chlamydiasis/gonorrhoea.
- Dysmenorrhoea = painful menstruation (most commonly reported disorder); Primary dysmenorrhoea caused by prostaglandins; Secondary dysmenorrhoea caused by endometriosis or uterine fibroids.
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