Human Reproductive System

1. Core Principle

  • Reproduction ensures species continuity.

  • Not required for individual survival.

  • Sexual reproduction:

    • Haploid gametes (n) → sperm + ovum

    • Fertilization → diploid zygote (2n)

2. Male Reproductive System

Primary Structures (Gonads)

  • Testes

    • Seminiferous tubules → spermatogenesis

    • Produce testosterone (androgen)

    • ~250 million sperm/day

    • Require temperature < body temp

  • Scrotum

    • Regulates temperature (thermoregulation)

Sperm Pathway

Testes → Epididymis → Vas deferens → Ejaculatory duct → Urethra → Penis

  • Epididymis

    • Sperm maturation + storage

  • Vas deferens

    • Transports sperm

Accessory Glands

  • Seminal vesicles

    • ~60% of semen

    • Fructose (energy), prostaglandins

  • Prostate gland

    • Alkaline fluid → neutralizes acidity

External Structure

  • Penis

    • Erectile tissue

    • Delivers sperm into female reproductive tract

  • Urethra

    • Shared pathway (urine + semen)

3. Female Reproductive System

Primary Structures (Gonads)

  • Ovaries

    • Produce ova (eggs)

    • Secrete estrogen + progesterone

    • Contain follicles (immature eggs)

Key Structures

  • Fallopian tubes (oviducts)

    • Site of fertilization

    • Cilia move ovum → uterus

  • Uterus

    • Endometrium (inner layer): implantation

    • Myometrium (muscle): contractions (labor)

  • Cervix

    • Regulates passage

    • Mucus changes across cycle

  • Vagina

    • Birth canal

    • Entry for sperm, exit for menstruation

4. Hormonal Control (Male)

Axis: Hypothalamus → Pituitary → Testes

  • GnRH (hypothalamus) → stimulates pituitary

  • FSH

    • Sperm maturation

  • LH

    • Stimulates testosterone production

Feedback

  • Testosterone ↑ → inhibits GnRH (negative feedback)

5. Hormonal Control (Female)

Key Hormones

  • GnRH → FSH + LH → Estrogen + Progesterone

6. Ovarian Cycle (≈28 days)

Phases

  1. Menstrual (Days 1–5)

    • Endometrium sheds

  2. Preovulatory (Follicular)

    • FSH → follicle growth

    • Estrogen ↑

  3. Ovulation (~Day 14)

    • LH surge → ovum release

  4. Postovulatory (Luteal)

    • Corpus luteum → progesterone

    • Prepares uterus

Outcomes

  • Fertilization → implantation → pregnancy

  • No fertilization → corpus luteum degenerates → menstruation

7. Fertilization and Development

Sequence

  • Fertilization (fallopian tube) → zygote

  • Cleavage → embryo

  • Implantation (~1 week)

Development Stages

  • Gastrulation

    • Endoderm, mesoderm, ectoderm

  • Neurulation

    • Neural tube → brain + spinal cord

8. Placenta and Exchange

  • Placenta

    • Nutrient + gas exchange

    • Hormone secretion

  • Umbilical cord

    • Arteries → waste out

    • Vein → oxygen/nutrients in

9. Pregnancy Hormones

  • Progesterone

    • Maintains uterine lining

  • Oxytocin

    • Uterine contractions (positive feedback)

  • Prolactin

    • Milk production

10. Birth (Parturition)

  • CRH → oxytocin + prostaglandins

  • Contractions intensify via positive feedback

  • Delivery occurs

11. Additional Concepts

Puberty (Male Example)

  • Testosterone → voice deepening, muscle growth, hair

Menopause

  • End of ovarian cycles

  • Hormone decline

Pheromones

  • Chemical signals affecting behavior (common in mammals)

12. Mammalian Reproductive Types

  • Placental mammals

    • Full internal development

  • Marsupials

    • Partial internal → pouch development

  • Monotremes

    • Egg-laying mammals

13. High-Yield Summary

  • Gonads = gamete production + hormone secretion

  • Fertilization = fallopian tube

  • Implantation = uterus (endometrium)

  • FSH/LH regulate both sexes

  • Negative feedback (male), cyclic variation (female)

  • Progesterone = pregnancy maintenance

  • Oxytocin = labor (positive feedback)

  • Placenta = exchange + endocrine function