Reproductive System - MBBS 1st Year Physiology Important Topics

1. Sex Determination and Differentiation

• Chromosomal sex (XX vs XY), genetic sex
• Role of SRY gene in testis determination
• Development of male and female internal/external genitalia
• Disorders: Klinefelter syndrome (47,XXY) and Turner syndrome (45,X) - these are very frequently asked in exams

2. Male Reproductive Physiology

• Seminiferous tubules (80% of testis) - spermatogenesis
• Leydig cells - testosterone synthesis
• Sertoli cell functions (very important short note topic):
  • Blood-testes barrier (tight junctions)
  • Nutrient supply to sperm
  • Secretion of androgen-binding protein (ABP)
  • Secretion of inhibin

• Three phases: mitosis of spermatogonia → meiosis → spermiogenesis
• Duration: ~64 days
• Role of FSH and testosterone
• Temperature requirement (35-36°C, why testes are in scrotum)
• Countercurrent heat exchange mechanism
• Cryptorchidism (undescended testes) and its effects

• Head (nucleus + acrosome with hydrolytic enzymes), midpiece (mitochondria), tail (flagellum)

• Secretions from seminal vesicles (fructose, prostaglandins - 60%), prostate (acid phosphatase, citric acid - 20%), bulbourethral glands (5%)
• Normal semen analysis values (useful as a short note / diagnostic tool topic)

• Capacitation: activation of sperm in female tract (~7 hours)
• Acrosome reaction: release of enzymes to penetrate zona pellucida

• See table below - mediated by testosterone vs. dihydrotestosterone (DHT)
• Testosterone: epididymis/vas deferens/seminal vesicle differentiation, muscle mass, pubertal growth spurt, spermatogenesis, libido, negative feedback on pituitary
• DHT: penis/scrotum/prostate differentiation, male hair pattern, male-pattern baldness, sebaceous glands
• 5-alpha reductase converts testosterone → DHT

• GnRH (pulsatile) → LH + FSH
• LH → Leydig cells → testosterone
• FSH → Sertoli cells → spermatogenesis + inhibin
• Negative feedback by testosterone (on hypothalamus + anterior pituitary) and inhibin (on anterior pituitary)

3. Female Reproductive Physiology

• Starts in fetal life (gestational weeks 8-9)
• 7 million oogonia at weeks 20-24, arrested at prophase of meiosis I
• At birth: 2 million oocytes; at puberty: 400,000; at menopause: nearly none
• First meiotic division completed at ovulation; second at fertilization
• Unlike males, females do NOT produce new oocytes after birth

• Graafian follicle development: primordial → primary → secondary → Graafian
• Two-cell, two-gonadotropin theory: Theca cells (LH → androgens) + Granulosa cells (FSH → aromatize androgens to estrogen)
• LH surge mechanism and ovulation
• Corpus luteum: formed from ruptured follicle; produces progesterone; regresses at day 28 unless fertilization occurs

• Hormonal control throughout the cycle (GnRH → FSH/LH → estrogen/progesterone → feedback)
• Indicators of ovulation: basal body temperature rise (~0.5°C), cervical mucus changes (Spinnbarkeit/ferning), LH surge in urine/blood
• Anovulatory cycles

• Development of female secondary sex characteristics
• Proliferative phase of endometrium
• Growth of uterus, fallopian tubes, vagina
• Breast development
• Positive feedback on LH at mid-cycle (LH surge)
• Bone density maintenance

• Secretory phase of endometrium
• Increases basal body temperature
• Cervical mucus thickening
• Breast alveolar development
• Inhibits uterine contractions (maintains pregnancy)
• Negative feedback on FSH/LH

4. Changes During Puberty

• Males: testicular enlargement, spermarche, growth of genitalia, voice deepening, muscle mass increase, pubic/axillary/facial hair (all androgen-driven)
• Females: thelarche (breast), pubarche (pubic hair), growth spurt, menarche (last)
• Tanner stages (know stages I-V)
• Role of GnRH pulse frequency increase at puberty

5. Menopause

• Ovarian follicle depletion → low estrogen + progesterone → high FSH + LH (loss of negative feedback)
• Symptoms: hot flushes, vaginal atrophy, osteoporosis, cardiovascular risk
• Average age ~51 years
• Perimenopause - irregular cycles before complete cessation

6. Placental Hormones and Maternal Physiology of Pregnancy (important)

• hCG (Human Chorionic Gonadotropin): secreted by syncytiotrophoblast from day 8; maintains corpus luteum; basis of pregnancy tests; peaks at 10-12 weeks
• hPL (Human Placental Lactogen / hCS): insulin antagonist, promotes fetal nutrition
• Progesterone and Estrogen: produced by placenta after 8-10 weeks (luteoplacental shift)
• Relaxin: softens pubic symphysis and cervix
• Maternal changes in pregnancy: increased blood volume, cardiac output, respiratory rate, GFR; decreased BP initially

7. Parturition

• Role of oxytocin and prostaglandins
• Ferguson reflex (cervical stretch → oxytocin release - positive feedback)
• Stages of labor (first, second, third)
• Role of progesterone withdrawal

8. Lactation

• Mammogenesis (breast development) - estrogen + progesterone + prolactin
• Milk secretion: prolactin (anterior pituitary)
• Milk ejection: oxytocin (posterior pituitary) via suckling reflex
• Colostrum (IgA-rich, first 3 days)
• Lactational amenorrhea mechanism

9. Contraception

• Oral contraceptive pills (OCPs): combined (estrogen + progesterone) - suppress LH surge, prevent ovulation; minipill (progesterone only)
• Intrauterine devices (IUDs)
• Male contraception: vasectomy, condoms
• Emergency contraception

10. Fertilization and Implantation (brief)

• Site of fertilization: ampulla of fallopian tube
• Zona reaction (prevents polyspermy)
• Implantation: day 6-7 after fertilization, in posterior wall of uterus

Priority Order for Exams (Most to Least Frequently Asked)

1. Menstrual cycle (almost always a long question)
2. Spermatogenesis (long or short question)
3. Functions of testosterone / estrogen / progesterone
4. Ovarian cycle (often paired with menstrual cycle)
5. Sertoli cell functions
6. Placental hormones (hCG, hPL)
7. Maternal physiology of pregnancy
8. Parturition
9. Lactation
10. Klinefelter and Turner syndrome
11. Corpus luteum - formation and fate
12. Semen composition and analysis
13. Menopause
14. Contraception

Recommended Textbooks

• Costanzo Physiology (most concise, exam-friendly)
• Guyton & Hall Medical Physiology (detailed, for concepts)
• Ganong's Review of Medical Physiology (good for MCQs)