Crash Course Reproduction

• Reproductive system


  The tissues, glands, and organs involved in producing offspring
• Components of the reproductive system


  • Primary, internal sex organs (gonads like testes and ovaries)
  • Sex hormones
  • Gametes (sperm and eggs)
  • Glands
  • Ducts
  • External genitalia
  • Particular brain parts
• Female reproductive anatomy


  • Vulva (mons pubis, labia majora, labia minora, vestibule)
  • Vagina
  • Ovaries
  • Fallopian tubes
  • Uterus
• Gametes


  Haploid cells with one set of chromosomes, formed by meiosis
• Ovarian follicles


  Tiny sac-like structures that each hold a single primary oocyte and supporting follicle cells
• Females are born with around 1 million primordial follicles
• Oocytes stop developing at birth and remain in the first stage of meiosis until puberty
• Oogenesis


  The process of egg creation, delayed until puberty
• Menstrual cycle


  What happens in the uterus to prepare for a fertilized egg
• Ovarian cycle


  The maturation of the follicle and egg, which drives the menstrual cycle
• Ovarian cycle


  1. Primordial follicles mature into late-tertiary follicles

  2. One follicle is selected to support a single, mature egg

  3. The rest undergo atresia (programmed self-destruction)
• Ovulation


  Follicle ruptures and ejects a single, mature oocyte
• Corpus luteum


  The structure the ruptured follicle morphs into, which releases hormones to prepare the uterus
• Menstrual cycle


  1. Shedding of the functional layer of the endometrium (days 1-5)

  2. Regeneration of the endometrium (days 6-14)

  3. Thickening of the endometrium if fertilization occurs (post-ovulation)
• Testes


  The gonads of the anatomical male, tasked with making male gametes, sperm, and the androgen hormone testosterone
• Testes

  • They are located outside the abdominal cavity, in the scrotum, because sperm are sensitive to temperature and require a lower temperature for proper spermatogenesis
  • Each testis is divided into about 250 sections called lobules, which are loaded with tightly-coiled seminiferous tubules where sperm are produced
• Spermatogenesis

  1. Spermatogonia cells divide to form primary spermatocytes

  2. Primary spermatocytes undergo meiosis I to form secondary spermatocytes

  3. Secondary spermatocytes undergo meiosis II to form round spermatids

  4. Spermatids undergo spermiogenesis to become mature sperm with a tail
• Sertoli cells


  Cells inside the seminiferous tubules that nourish developing sperm cells
• Leydig cells


  Cells that secrete testosterone
• Hormonal cascade triggering spermatogenesis

  1. Hypothalamus releases GnRH

  2. Anterior pituitary releases FSH and LH

  3. LH stimulates Leydig cells to release testosterone

  4. FSH triggers Sertoli cells to release androgen-binding protein, creating high local concentrations of testosterone

  5. Testosterone targets spermatogonia stem cells to begin dividing and producing sperm
• Spermatogonia


  Stem cells that divide to produce sperm. Type A cells stay near the basal lamina and keep dividing, while Type B cells get pushed down the tubule and turn into primary spermatocytes.
• Spermatids


  Haploid cells produced by meiosis that undergo spermiogenesis to become mature sperm with a tail
• Sperm transport and maturation


  1. Seminiferous tubules contract to squeeze sperm into the rete testis

  2. Sperm travel through the epididymis where they gain motility and continue to mature over 2-3 weeks

  3. Sperm leave the epididymis and travel through the vas deferens, ejaculatory ducts, and urethra during ejaculation
• Seminal vesicles


  Glands that secrete fluid to nourish and transport sperm, and contain enzymes and prostaglandins to help sperm
• Prostate gland


  Gland that secretes fluid to keep semen liquefied and easier for sperm to swim through
• Bulbourethral glands


  Glands that secrete mucus to clear the urethra before ejaculation
• Penis


  Organ containing erectile tissue that becomes rigid during sexual arousal to facilitate penetration of the vagina and delivery of sperm