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The Reproductive System

Male Reproductive System Anatomy and Physiology

  • Gametes are produced in gonads (testes in males, ovaries in females).
  • Male gametes are called sperm, produced via spermatogenesis in the seminiferous tubules of the testes.
  • Scrotum: A muscular sac housing the testes outside the body, maintaining a lower temperature for efficient sperm production.
  • Spermatogenesis:
    • Begins with diploid spermatogonia undergoing mitosis.
    • Primary spermatocytes undergo meiosis I and II to form haploid spermatids.
    • Spermatids transform into spermatozoa (sperm) during spermiogenesis.
  • Sperm Structure: Head (containing DNA), mid-piece (mitochondria for energy), and tail (flagellum for motility).
  • Epididymis: Matures and stores sperm.
  • Ductus Deferens: Transports sperm from the epididymis, through the spermatic cord, to the ejaculatory duct.
  • Accessory Glands:
    • Seminal vesicles: Contribute fructose-rich fluid.
    • Prostate gland: Adds alkaline secretions.
    • Bulbourethral glands: Secrete lubricating mucus.
  • Semen: Combination of sperm and seminal fluids.
  • Penis: Male copulatory organ; erectile tissue (corpora cavernosa and corpus spongiosum) fills with blood during arousal.
  • Testosterone:
    • Produced by Leydig cells.
    • Regulates sex organs, sex drive, and physical changes during puberty.
    • Production controlled by a negative feedback loop involving the hypothalamus and pituitary gland.
    • Hypothalamus releases GnRH, which stimulates the anterior pituitary to release LH and FSH.
    • LH stimulates Leydig cells to produce testosterone. FSH promotes spermatogenesis.

Female Reproductive System Anatomy and Physiology

  • Vulva: External female genitalia.
  • Vagina: Canal for intercourse, menses, and childbirth.
  • Ovaries: Female gonads that produce oocytes (via oogenesis) and sex hormones (estrogen and progesterone).
  • Oogenesis:
    • Oogonia divide mitotically to form primary oocytes before birth.
    • Primary oocytes undergo meiosis I (arrested until puberty).
    • Meiosis II completes only if fertilization occurs, resulting in a haploid ovum.
  • Follicles: Oocytes are surrounded by supporting cells.
  • Folliculogenesis:
    • Primordial follicles develop into primary, secondary, and tertiary follicles.
    • Early tertiary follicles grow due to FSH stimulation.
    • Granulosa and theca cells produce estrogen.
    • High estrogen levels trigger negative feedback, reducing FSH and LH, leading to atresia in most follicles.
    • The dominant follicle survives and produces more estrogen, triggering positive feedback and the LH surge.
  • Ovulation:
    • The LH surge induces the release of a secondary oocyte.
  • Corpus Luteum:
    • Forms from the remaining granulosa cells after ovulation.
    • Secretes progesterone.
  • In absence of pregnancy, the corpus luteum degrades which lowers the hormones and results in menses.
  • Uterine Tubes (Fallopian Tubes): Transport the oocyte to the uterus; fertilization occurs here.
  • Uterus:
    • Fundus, body, and cervix regions.
    • Three layers: perimetrium, myometrium, and endometrium.
    • The endometrium thickens in response to estrogen and progesterone.
    • The endometrium sheds during menstruation (menses) if fertilization doesn't occur.
  • Menstrual Cycle:
    • Menses phase: Endometrial lining is shed.
    • Proliferative phase: Endometrium rebuilds under estrogen influence.
    • Secretory phase: Endometrium prepares for implantation under progesterone influence.
  • Breasts: Accessory organs for lactation; mammary glands produce milk.

Development of Reproductive Systems

  • Sex Determination:
    • Females are the "fundamental" sex.
    • The SRY gene on the Y chromosome triggers male development by promoting testis formation and suppressing female development.
  • Hormonal Influence:
    • Testosterone stimulates male reproductive structure development.
    • In the absence of testosterone, female structures develop.
  • Puberty:
    • Hypothalamus releases GnRH.
    • Anterior pituitary releases LH and FSH.
    • Increased LH and FSH stimulate the gonads to release sex hormones.
    • Leads to maturation of reproductive organs and development of secondary sex characteristics.