(a) Give an account of hormonal regulation of menstruation in human females. (20 marks) (b) Explain the source(s) and functions…

(a) Hormonal regulation of menstruation Menstruation is cyclic endometrial shedding controlled by the hypothalamic–pituitary–ovarian (HPO) axis. The hypothalamus releases GnRH in pulses, stimulating the anterior pituitary to secrete FSH and LH. In the early follicular phase, low estrogen and progesterone allow FSH to rise. FSH acts on ovarian follicles, increasing granulosa cell proliferation, aromatase activity and estradiol synthesis. Rising estradiol first exerts negative feedback on FSH; after reaching a threshold for about 50 hours, it gives positive feedback on LH, causing the pre-ovulatory LH surge. This surge triggers ovulation, completion of meiosis I in the dominant oocyte, and luteinisation of the ruptured follicle. The corpus luteum then secretes progesterone and estradiol. Progesterone converts the endometrium to a secretory, receptive state and maintains it. If fertilisation does not occur, luteolysis begins; progesterone and estradiol fall, spiral arteries constrict, and the functional layer of the endometrium breaks down, causing menstrual bleeding. The basalis layer regenerates the next cycle. The fall in steroids removes negative feedback, so GnRH, FSH and LH rise again and recruit the next follicular cohort. Thus the follicular phase is dominated by estradiol, the luteal phase by progesterone, and the menstrual phase by low steroid levels.

(b) B vitamins Thiamine (vitamin B₁) comes from whole grains, legumes, nuts, yeast and lean meats. It is converted to thiamine pyrophosphate (TPP), a coenzyme for pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase and transketolase. These TPP-dependent decarboxylation reactions are central to citric acid cycle and pentose phosphate pathway energy metabolism and support nerve conduction. Deficiency causes beriberi and Wernicke–Korsakoff syndrome. Riboflavin (vitamin B₂) is abundant in milk, eggs, green leafy vegetables, yeast and organ meats. It forms FMN and FAD, prosthetic groups of dehydrogenases in the electron transport chain, including NADH dehydrogenase and succinate dehydrogenase, making it essential for oxidative phosphorylation. Riboflavin also supports antioxidant defence through glutathione reductase, which regenerates reduced glutathione and protects cells from oxidative damage. Cobalamin (vitamin B₁₂) occurs only in animal foods such as liver, kidney, dairy, eggs and fish; it is absent from unfortified plant foods, a concern for Indian vegetarians. It acts as coenzyme for methylmalonyl-CoA mutase, converting methylmalonyl-CoA to succinyl-CoA, and for methionine synthase, transferring a methyl group from 5-methyltetrahydrofolate to homocysteine. This maintains folate cycle function and S-adenosylmethionine supply for myelin synthesis. Deficiency causes megaloblastic anaemia, neurological damage and, in pernicious anaemia, failure of intrinsic factor-mediated absorption.

(c) Oogenesis Oogenesis in human females has three phases. In the multiplication phase, primordial germ cells migrate to the gonadal ridge and divide mitotically to form oogonia. During fetal life, oogonia enter meiosis and become primary oocytes, which arrest in diplotene of prophase I (dictyate stage). At birth and in childhood, these oocytes remain relatively small and quiescent in primordial follicles. In the growth phase, after puberty, cyclic FSH recruits a cohort of follicles; the oocyte enlarges, accumulates cytoplasm, organelles and yolk-like precursors, and the follicle develops granulosa and theca layers. Usually one follicle becomes dominant. In the maturation phase, the pre-ovulatory LH surge, supported by estradiol, causes the dominant primary oocyte to resume meiosis I, extrude the first polar body and become a secondary oocyte. It begins meiosis II and arrests at metaphase II. It is ovulated in this state; meiosis II completes only if fertilisation occurs, producing the ovum and second polar body. Thus oogenesis is hormonally gated, with meiotic arrest preserving oocyte quality until the reproductive window.

Conclusion Together, these processes show that human reproduction depends on precise neuroendocrine feedback, follicular development and micronutrient support; disruption of hormonal regulation or B-vitamin status can impair fertility, pregnancy and health.