02Class 12 Biology
Human Reproduction short notes
Short notes on the human reproductive systems, gametogenesis, the menstrual cycle and pregnancy. It's a high-yield chapter for NEET, and the hormones are its most tested part.
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Male system
- Sperm form in the seminiferous tubules of the testes.
- Leydig cells make androgens, and Sertoli cells nourish developing sperm.
- Testes sit in the scrotum, where it's about 2 to 2.5 °C cooler than the body.
- Spermatogenesis starts at puberty, and is controlled by GnRH, LH and FSH.
Female system and gametogenesis
- Oogenesis starts before birth, and primary oocytes pause in prophase I until puberty.
- One oogonium gives one ovum and polar bodies, while one spermatogonium gives four sperm.
- A secondary oocyte is released at ovulation, and finishes meiosis II only if a sperm enters it.
Menstrual cycle (about 28 days)
- Menstrual phase (days 1 to 5): the uterine lining breaks down.
- Follicular phase (days 5 to 13): the follicle matures and the lining regrows, driven by FSH and estrogen.
- Ovulation (about day 14): triggered by an LH surge.
- Luteal phase (days 15 to 28): the corpus luteum makes progesterone, which keeps the lining ready.
Fertilisation and pregnancy
- Fertilisation happens in the ampullary-isthmic junction of the fallopian tube.
- The sequence after that is zygote, morula, blastocyst, then implantation in the endometrium.
- The placenta makes hCG, hPL, estrogen and progesterone. The ovary makes relaxin late in pregnancy.
- Gestation lasts about nine months, and oxytocin drives contractions during birth.
Where students slip up
- Confusing LH and FSH. The LH surge triggers ovulation.
- Saying a mature ovum is released. It's a secondary oocyte.
- Mixing up Leydig cells (hormones) and Sertoli cells (nourishment).
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