Reproductive Physiology and Pregnancy
Key concepts of the gonadal axes, menstrual cycle, fertilisation and early pregnancy endocrinology.
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Questions Covered in This Set
10 cards to master
Why does continuous GnRH (e.g. leuprolide) suppress rather than stimulate the gonads?
Continuous exposure downregulates gonadotroph GnRH receptors, collapsing LH and FSH — a 'chemical castration' used in prostate cancer, endometriosis and precocious puberty. Only pulsatile GnRH stimulates.
Two-cell, two-gonadotropin model
LH drives the theca cell to make androstenedione; FSH drives the granulosa cell to aromatise it into oestradiol.
Which hormone selectively inhibits FSH in the male axis?
Inhibin B from Sertoli cells (testosterone gives broader negative feedback on hypothalamus and pituitary).
Why does anabolic steroid abuse cause infertility and testicular atrophy?
Exogenous testosterone suppresses LH/FSH, so intratesticular testosterone (normally ~100× plasma) falls — spermatogenesis fails. Semen changes appear 2–3 months later since spermatogenesis takes ~74 days.
Which hormone closes the epiphyses in both sexes?
Oestradiol (from aromatisation of testosterone), not testosterone itself.
What triggers the mid-cycle LH surge?
Oestradiol above ~200 pg/mL sustained for ~36–48 h flips feedback from negative to positive, producing the LH spike; ovulation follows ~36 h after surge onset.
Why is single ovulation the norm?
The dominant follicle's high oestradiol negatively feeds back on FSH, starving the sister follicles.
Which phase of the cycle is fixed in length?
The luteal phase (14 ± 2 days); cycle-length variability is almost entirely follicular.
How do you confirm ovulation clinically?
Basal body temperature rise of ~0.3–0.5 °C and a mid-luteal progesterone >3 ng/mL about a week after suspected ovulation.
Role of hCG and the luteo-placental shift
Syncytiotrophoblast hCG (an LH analogue) sustains the corpus luteum so progesterone never withdraws; hCG doubles ~every 48 h, peaks at 8–10 weeks, then the placenta assumes progesterone production.
