Chapter 12 — Human Reproduction
Key Concepts Quick Recap
| Term | Definition |
|---|
| Seminiferous tubules | Site of sperm production in testes |
| Sertoli cells | Nurse cells in seminiferous tubules; nourish developing sperms |
| Leydig cells (interstitial cells) | Between seminiferous tubules; produce testosterone |
| Acrosome | Cap on sperm head; contains enzymes to penetrate egg |
| Graafian follicle | Mature ovarian follicle; releases ovum at ovulation |
| Corpus luteum | Yellow body formed from ruptured follicle; secretes progesterone |
| Ovulation | Release of ovum on day 14 of menstrual cycle (LH surge) |
| Fertilisation | Sperm + egg; normally in fallopian tube (ampullary region) |
| Implantation | Blastocyst embeds in uterine endometrium (day 7 after fertilisation) |
| hCG | Human chorionic gonadotropin; maintains corpus luteum in pregnancy |
I. Choose the Best Answer (MCQs)
1. The site of sperm production in the human male is: (a) Epididymis (b) Prostate gland (c) Seminiferous tubules (d) Vas deferens
Answer(c) Seminiferous tubules Seminiferous tubules (in testis) are the site of spermatogenesis. Each testis has ~250 lobules, each with 1-3 seminiferous tubules. Sertoli cells in the tubules nourish developing sperms. Leydig cells (between tubules) secrete testosterone.
2. Testosterone is produced by: (a) Sertoli cells (b) Leydig (interstitial) cells (c) Seminiferous tubule cells (d) Pituitary gland
Answer(b) Leydig (interstitial) cells Leydig cells lie between seminiferous tubules in the testis interstitium. They produce testosterone (stimulated by LH from anterior pituitary). Testosterone: maintains spermatogenesis, secondary sexual characteristics, libido.
3. Ovulation in human females occurs on approximately day: (a) 7 (b) 14 (c) 21 (d) 28
Answer(b) 14 In a 28-day cycle, ovulation occurs on day 14 in response to LH surge (from anterior pituitary). The Graafian follicle ruptures → secondary oocyte released into fallopian tube. This is the most fertile period. LH surge is triggered by peak oestrogen from the mature follicle.
4. The corpus luteum produces: (a) Oestrogen only (b) Progesterone mainly (c) FSH (d) LH
Answer(b) Progesterone mainly After ovulation, the ruptured follicle transforms into corpus luteum (yellow body). It secretes progesterone (mainly) and oestrogen. Progesterone: maintains endometrium for implantation, prevents further ovulation during pregnancy. If fertilisation doesn't occur → corpus luteum degenerates (day 26-28) → progesterone drops → menstruation begins.
5. Fertilisation normally occurs in: (a) Uterus (b) Ovary (c) Fallopian tube (ampullary region) (d) Cervix
Answer(c) Fallopian tube (ampullary region) Fertilisation takes place in the ampullary region (widest part) of the fallopian tube. The ovum is viable for ~12-24 hours after ovulation; sperm can survive up to 72 hours in the female reproductive tract. Ectopic pregnancy: implantation in fallopian tube instead of uterus (medical emergency).
6. Implantation of the blastocyst occurs in the: (a) Ovary (b) Fallopian tube (c) Uterus (endometrium) (d) Cervix
Answer(c) Uterus (endometrium) After fertilisation (~day 1), the zygote undergoes cleavage while moving through the fallopian tube. By ~day 4-5: morula. Day 6-7: blastocyst. Blastocyst implants in the uterine endometrium on day 6-7. The inner cell mass (embryoblast) → embryo; outer trophoblast → placenta.
7. Human chorionic gonadotropin (hCG) is produced by: (a) Corpus luteum (b) Anterior pituitary (c) Trophoblast cells of placenta (d) Ovary
Answer(c) Trophoblast cells of placenta hCG is produced by the trophoblast after implantation. Function: maintains corpus luteum during early pregnancy → continues progesterone production. hCG appears in urine within 8-10 days of fertilisation — detected by pregnancy tests. hCG levels peak at ~10 weeks, then decline as placenta takes over progesterone production.
II. Short Answer Questions
Q1. Describe spermatogenesis.
Answer
Spermatogenesis: formation of spermatozoa in seminiferous tubules; begins at puberty.
Stages: 1. Spermatogonia (2n): Germ cells on basement membrane of seminiferous tubule; undergo mitosis to maintain stem cell population and produce primary spermatocytes.
2. Primary spermatocyte (2n): Undergoes meiosis I → two secondary spermatocytes (n) — this is the longest stage.
3. Secondary spermatocyte (n): Undergoes meiosis II → two spermatids (n) each.
4. Spermatid (n): Haploid; non-motile. Undergo spermiogenesis (morphological transformation) → spermatozoa.
Result1 spermatogonium → 4 spermatozoa.
Structure of sperm:
- Head: Nucleus (contains DNA) + Acrosome (lysosomal enzymes: hyaluronidase, acrosin — penetrate zona pellucida of egg).
- Middle piece: Mitochondria (ATP for tail movement).
- Tail (flagellum): Propulsion.
Duration: ~64-74 days in humans.
Q2. Describe the phases of the menstrual cycle.
Answer
Average cycle: 28 days.
Phase 1 — Menstrual phase (Day 1-5):
- Corpus luteum degenerates → progesterone and oestrogen fall.
- Endometrium (functional layer) sheds → menstrual flow (~50-80 mL blood + mucus + endometrium).
- FSH begins to rise.
Phase 2 — Follicular (Proliferative) phase (Day 6-13):
- FSH → several ovarian follicles grow → one becomes dominant (Graafian follicle).
- Oestrogen rises → endometrium thickens (proliferates).
- Oestrogen peaks → triggers LH surge.
Phase 3 — Ovulatory phase (Day 14):
- LH surge → Graafian follicle ruptures → secondary oocyte released.
- Ovum swept into fallopian tube by cilia and fimbriae.
Phase 4 — Luteal (Secretory) phase (Day 15-28):
- Ruptured follicle → corpus luteum.
- Progesterone (mainly) + oestrogen → endometrium becomes thick, glandular (secretory).
- Prepares uterus for implantation.
- If no fertilisation: corpus luteum degenerates → hormone levels fall → cycle repeats.
Common Mistakes
- Confusing Sertoli cells (nourish sperms) and Leydig cells (produce testosterone).
- Saying ovulation occurs on day 7 — ovulation is day 14 (in a 28-day cycle).
- Saying corpus luteum produces FSH or LH — it produces progesterone.
- Confusing site of fertilisation (fallopian tube) with site of implantation (uterus).
- Forgetting hCG is the basis of pregnancy tests (produced by trophoblast, not pituitary).
Exam Checklist
- Spermatogenesis: spermatogonia → primary spermatocyte → secondary spermatocyte → spermatid → sperm.
- 1 primary spermatocyte → 4 sperms; 1 primary oocyte → 1 egg + 3 polar bodies.
- Leydig cells: testosterone; Sertoli cells: nourish sperms.
- Menstrual cycle: menstrual (1-5) → follicular/proliferative (6-13) → ovulation (14, LH surge) → luteal (15-28, progesterone).
- Fertilisation: fallopian tube; implantation: uterine endometrium (day 6-7).
- hCG: trophoblast → maintains corpus luteum → detected in pregnancy tests.
