Ch 3 covers the human reproductive system — male and female anatomy, gametogenesis (spermatogenesis and oogenesis), menstrual cycle, fertilisation, implantation, and embryonic development.
Spermatogenesis: spermatogonia → primary spermatocytes (meiosis I) → secondary spermatocytes (meiosis II) → spermatids → spermatozoa (spermiogenesis). In seminiferous tubules, supported by Sertoli cells. Hormonal control: GnRH → FSH + LH → testosterone. Oogenesis: oogonia → primary oocyte (arrested in prophase I at birth) → secondary oocyte (arrested in metaphase II, released at ovulation) → completes meiosis II only upon fertilisation.
Menstrual phase (days 1-5): shedding. Follicular phase (days 6-13): FSH → follicle growth, oestrogen rises. Ovulation (day 14): LH surge. Luteal phase (days 15-28): corpus luteum → progesterone. Fertilisation in ampulla of fallopian tube. Zygote → morula → blastocyst → implantation (~7 days). Embryonic development: gastrulation → 3 germ layers → organogenesis.
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After implantation, the trophoblast secretes hCG (human chorionic gonadotrophin) which maintains the corpus luteum. The corpus luteum continues producing progesterone, which inhibits GnRH/FSH/LH, preventing new follicle development and ovulation. Later, the placenta takes over progesterone production. High progesterone levels maintain the endometrium and suppress the menstrual cycle throughout pregnancy.
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