3.5 The Reproductive System

Male Reproductive System

  • Organs: Testes (sperm, testosterone), Scrotum (holds testes), Epididymis (sperm maturation/storage), Vas Deferens (sperm transport), Urethra (sperm/urine exit), Penis.
  • Accessory Glands: Seminal Vesicles (fructose), Prostate Gland (alkaline fluid), Bulbourethral Glands (lubrication).

Hormonal Control of Spermatogenesis

  1. Hypothalamus releases GnRH.
  2. GnRH stimulates Anterior Pituitary to release FSH and LH.
  3. LH stimulates Leydig cells to produce Testosterone.
  4. FSH stimulates Sertoli cells to nourish sperm and produce ABP/Inhibin.
  5. Testosterone and Inhibin provide negative feedback.

Female Reproductive System

  • Organs: Ovaries (eggs, estrogen, progesterone), Fallopian Tubes (egg transport, fertilization site), Uterus (fetus development), Cervix, Vagina.

Gametes: Sperm and Egg

Feature Sperm Egg (Ovum)
Size Microscopic Largest human cell
Motility Motile (tail) Non-motile
Structure Head, midpiece, tail Round, nucleus, cytoplasm, zona pellucida

Key Processes in Reproduction

  • Spermatogenesis: Sperm production.
  • Oogenesis: Egg production.
  • Fertilization: Sperm + Egg = Zygote.
  • Implantation: Zygote (blastocyst) attaches to uterine wall.
  • Gestation: Pregnancy period.
  • Parturition: Childbirth.

The Menstrual Cycle: Hormonal Control

  1. Follicular Phase: FSH stimulates follicle growth; follicles produce estrogen (thickens endometrium).
  2. Ovulation: LH surge triggers egg release.
  3. Luteal Phase: Ruptured follicle forms corpus luteum (produces progesterone, estrogen).
  4. Menstruation: If no fertilization, corpus luteum degenerates, hormone levels drop, uterine lining sheds.

Pregnancy and Development

  • Placenta: Temporary organ connecting fetus to uterus.
    • Functions: Nutrition, respiration, excretion, endocrine (hCG, estrogen, progesterone).
  • Fetal Membranes: Amnion (forms amniotic sac).
  • Amniotic Fluid: Cushions and protects fetus.

Twins

  • Identical (Monozygotic): Single fertilized egg splits; genetically identical, same sex.
  • Fraternal (Dizygotic): Two separate eggs fertilized by two different sperm; no more genetically similar than siblings.