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Topic 9

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Reproductive and Developmental Physiology

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Reproductive and Developmental Physiology — Key Facts for FMGE Core concept: The HPG axis regulates sex hormone production and gametogenesis; understand the menstrual cycle phases and hormonal changes High-yield point: Estrogen is produced by developing follicles; progesterone by corpus luteum; LH surge triggers ovulation; understand feedback loops ⚡ Exam tip: The LH surge causes ovulation ~36 hours after the surge begins; progesterone makes basal body temperature rise

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Reproductive and Developmental Physiology — FMGE Study Guide

Male Reproductive Physiology

Testes

  • Seminiferous tubules: Spermatogenesis (spermatogonia → spermatozoa)
  • Sertoli cells: Support germ cells; secrete inhibin, androgen-binding protein (ABP)
  • Leydig cells: Produce testosterone (stimulated by LH)

Spermatogenesis

  • Spermatogonia (2n) → Primary spermatocytes (2n) → Secondary spermatocytes (n) → Spermatids (n) → Spermatozoa (n)
  • Takes ~74 days
  • Requires FSH, testosterone, zinc, vitamin A
  • Sertoli cells: Provide nourishment, create blood-testis barrier

Testosterone

  • Actions: Spermatogenesis, male secondary sexual characteristics, anabolic effects, libido
  • Converted to DHT by 5α-reductase in target tissues (prostate, skin)
  • Negative feedback: On LH (via hypothalamus and pituitary)

Male Hormonal Regulation

  • GnRH (pulsatile, every 90 min) → LH + FSH
  • LH: Stimulates testosterone production by Leydig cells
  • FSH: Stimulates spermatogenesis (via Sertoli cells) + inhibin B
  • Inhibin B: Feedback on FSH secretion

Erectile Function

  • Parasympathetic (NO → cGMP → smooth muscle relaxation → erection)
  • Sympathetic (α1 → vasoconstriction → detumescence)

Female Reproductive Physiology

Ovarian Cycle

Follicular phase (Days 1-14):

  • FSH rises → recruits follicles (5-7 follicles start developing)
  • Estrogen rises from growing follicles → proliferative endometrium
  • Negative feedback on FSH (only the follicle with most FSH receptors continues)
  • One dominant follicle selected by Day 5-7; others become atretic

Ovulation (Day 14):

  • Estrogen peak → positive feedback on LH → LH surge
  • LH surge causes: Resumption of meiosis I → ovulation 36 hours after surge
  • Also triggers: Granulosa cell luteinization, formation of corpus luteum

Luteal phase (Days 15-28):

  • Corpus luteum produces progesterone + estrogen
  • Progesterone: Transform endometrium to secretory (prepares for implantation)
  • If no pregnancy: Corpus luteum degenerates → estrogen and progesterone drop → menses
  • If pregnancy: hCG from trophoblast maintains corpus luteum

Hormonal Changes During Cycle

PhaseEstrogenProgesteroneLHFSH
Early follicularLowLowLowRising
Mid-follicularRisingLowLowPeak then drop
Pre-ovulatoryHigh (peak)LowLH surgeLow
LutealHigh (second rise)HighLowLow

Endometrial Changes

  • Proliferative phase (estrogen): Regeneration, elongation of glands
  • Secretory phase (progesterone): Tortuous glands, glycogen accumulation, edema
  • Menstruation: Spiral arteries constrict → ischemia → desquamation

Contraception Methods

  • Combined OCPs (estrogen + progestin): Negative feedback → ↓FSH/LH → no LH surge → no ovulation; also thicken cervical mucus, thin endometrium
  • Progestin-only: Thickens mucus, impairs implantation
  • Copper IUD: Spermotoxic effect; prevents fertilization
  • Mirena (levonorgestrel IUD): Thickens mucus, thins endometrium
  • Emergency contraception: High-dose progestin or ulipristal (progesterone antagonist/antagonist)

Pregnancy and Lactation

Fertilization

  • Sperm capacitation in female reproductive tract
  • Acrosome reaction releases enzymes to penetrate zona pellucida
  • Zygote forms → cleavage → morula → blastocyst (Day 5)
  • Implantation: Blastocyst attaches to endometrial epithelium (Day 6-12)

hCG

  • Human chorionic gonadotropin: Produced by trophoblast
  • Maintains corpus luteum → maintains progesterone → maintains pregnancy
  • Detected in blood/urine ~10 days after conception
  • Basis for pregnancy tests

Placenta

  • Produces: hCG, estrogen, progesterone, hPL (human placental lactogen), relaxin
  • Function: Gas exchange, nutrient transfer, waste removal, hormone production

Lactation

Prolactin:

  • Stimulates milk production
  • ↑during pregnancy but milk not produced (progesterone blocks prolactin’s effect)
  • After delivery, progesterone drops → prolactin can act → lactation
  • Suckling stimulates prolactin release (maintains lactation)
  • Dopamine inhibits prolactin (bromocriptine stops lactation)

Oxytocin:

  • Stimulates milk ejection (let-down reflex)
  • Stimulated by suckling; also by uterine distension post-delivery
  • Stimulates uterine contractions (used to control postpartum hemorrhage)

Milk composition:

  • Lactose: Primary carbohydrate
  • Proteins: Whey (lactoalbumin) > casein
  • Fats: Medium-chain triglycerides
  • Immunoglobulins: IgA provides passive immunity

Sexual Differentiation

Genetic Determination

  • 46,XY: SRY gene on Y chromosome → testes formation
  • 46,XX: No SRY → ovaries form

Gonadal Differentiation

  • Testes: Produce testosterone (Leydig cells) and Anti-Müllerian hormone (Sertoli cells)
  • Ovaries: Develop in absence of testes

phenotypic Differentiation

Male:

  • AMH causes regression of Müllerian ducts
  • Testosterone → Wolffian duct development (epididymis, vas deferens, seminal vesicles)
  • DHT → male external genitalia (penis, scrotum, prostate)

Female:

  • No AMH → Müllerian ducts develop (uterus, fallopian tubes, upper vagina)
  • No testosterone → Wolffian ducts regress
  • Default external genitalia (clitoris, labia)

Disorders

  • Androgen Insensitivity Syndrome (46,XY): Testes produce testosterone but receptor non-functional → female phenotype, blind-ending vagina, no uterus, testes in abdomen → risk of gonadoblastoma
  • 5α-Reductase deficiency: Cannot convert testosterone to DHT → ambiguous genitalia at birth, virilization at puberty
  • Congenital adrenal hyperplasia (21-hydroxylase deficiency): Excess androgens → virilization of genetic females

Puberty

Male Puberty

  • Tanner staging: 1-5 (pre-pubertal to adult)
  • First sign: Testicular enlargement (Tanner 2)
  • Growth spurt: Later in puberty for males
  • Hormonal changes: ↑LH, ↑FSH, ↑testosterone

Female Puberty

  • First sign: Breast development (thelarche - Tanner 2)
  • Menarche: Usually at Tanner 3-4
  • Growth spurt: Earlier than males
  • Hormonal changes: ↑estrogen, ↑LH, ↑FSH

Precocious Puberty

  • Definition: <8 years in girls, <9 years in boys
  • Central (gonadotropin-dependent): Early activation of HPG axis
  • Peripheral (gonadotropin-independent): Sex steroid production independent of HPG axis

Delayed Puberty

  • Definition: No breast development by age 13 in girls, no testicular enlargement by age 14 in boys
  • Causes: Constitutional delay, hypogonadotropic hypogonadism (Kallmann syndrome), hypergonadotropic hypogonadism (Turner, Klinefelter)

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