Physiology
Reproductive Physiology
Reproductive physiology for MBBS and NEET-PG: the reproductive axis, spermatogenesis, menstrual cycle and ovulation, pregnancy hormones and lactation, mapped to NMC codes PY9.
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Reproductive Physiology
Reproductive physiology for MBBS and NEET-PG: the reproductive axis, spermatogenesis, menstrual cycle and ovulation, pregnancy hormones and lactation, mapped to NMC codes PY9.
Reproductive physiology covers the control of the male and female reproductive systems. It deals with the hypothalamic-pituitary-gonadal axis, spermatogenesis, the menstrual cycle and ovulation, the hormones of pregnancy, and lactation.
High-yield: Reproductive Physiology
- Puberty begins with the pulsatile release of gonadotropin-releasing hormone from the hypothalamus.
- FSH and LH from the anterior pituitary drive the gonads in both sexes.
- In the male, testosterone from the Leydig cells supports spermatogenesis and secondary sexual characters.
- The Sertoli cells nourish developing sperm and secrete inhibin, which suppresses FSH.
- Spermatogenesis takes about 74 days and needs a temperature a little below body core.
- The menstrual cycle has a follicular phase, ovulation and a luteal phase, averaging about 28 days.
- Ovulation is triggered by the LH surge, which follows the rise in oestrogen from the dominant follicle.
- The corpus luteum secretes progesterone, which prepares and maintains the endometrium.
- If fertilisation does not occur, the corpus luteum regresses and menstruation follows the fall in progesterone.
- Human chorionic gonadotropin from the early placenta rescues the corpus luteum and is the basis of pregnancy tests.
- The placenta takes over hormone production and supports the pregnancy after the first trimester.
- Oxytocin drives uterine contractions in labour and the milk ejection reflex.
- Prolactin promotes milk production, while oxytocin causes milk let-down.
- Oestrogen and progesterone provide negative feedback on the hypothalamus and pituitary for most of the cycle.
Menstrual cycle hormones
- **FSH:** Stimulates follicular growth in the follicular phase.
- **LH surge:** Triggers ovulation after the oestrogen peak.
- **Progesterone:** From the corpus luteum; maintains the endometrium in the luteal phase.
- **hCG:** From the early placenta; rescues the corpus luteum; basis of pregnancy tests.
NMC competencies in this chapter
- **PY9.1:** Overview of the reproductive system and puberty
- **PY9.2:** Male reproductive physiology and spermatogenesis
- **PY9.4:** Female reproductive physiology and the ovarian cycle
- **PY9.5:** The menstrual cycle and ovulation
- **PY9.7:** Physiology of pregnancy
- **PY9.9:** Physiology of parturition
- **PY9.10:** Lactation and its control
- **PY9.12:** Physiology of contraception
Frequently Asked Questions
What triggers ovulation?
A surge of luteinising hormone from the pituitary, driven by rising oestrogen from the dominant follicle, triggers ovulation at about the middle of the cycle.
What is the role of the corpus luteum?
The corpus luteum forms after ovulation and secretes progesterone, which prepares and maintains the endometrium. If pregnancy does not occur, it regresses and menstruation follows.
Why is hCG used in pregnancy tests?
Human chorionic gonadotropin is released by the early placenta soon after implantation, so its presence in blood or urine is an early and reliable marker of pregnancy.
How is lactation controlled?
Prolactin from the anterior pituitary stimulates milk production, and oxytocin from the posterior pituitary causes milk ejection during suckling.
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