Human Reproduction — Class 12 Biology

This chapter describes the structure and functioning of the human reproductive system and the events of reproduction. The male system includes the testes, where spermatogenesis produces sperm in the seminiferous tubules under the influence of FSH, LH and testosterone, along with accessory ducts and glands that contribute to semen. The female system includes the ovaries, where oogenesis and folliculogenesis occur, fallopian tubes, uterus, vagina and accessory structures. Gametogenesis converts germ cells into haploid gametes; a mature sperm has a head, middle piece and tail, while the secondary oocyte is released at ovulation. The menstrual cycle, controlled by the hypothalamus-pituitary-ovary axis (GnRH, FSH, LH, estrogen, progesterone), involves the follicular, ovulatory and luteal phases, with menstruation occurring if fertilisation fails. Fertilisation in the ampulla forms a zygote, which undergoes cleavage to form a blastocyst that implants in the uterine wall. Embryonic development establishes the three germ layers and the placenta, the structural and functional link supplying nutrients and removing wastes, also acting as an endocrine organ. Gestation culminates in parturition, triggered by the foetal-placental signals and oxytocin, followed by lactation, with colostrum providing antibodies to the newborn.