Reproductive System Summary

Sex Determination

• Ovum (XX) + Sperm (XY) leads to Zygote.
• SRY gene on Y chromosome determines sex.
  • Presence leads to testes development.
  • Absence leads to ovaries development.

Development of Sex Organs

• SRY gene is the sex-determining region on the Y chromosome.
• Homologous structures develop differently in males and females.

Male Reproductive System

• Testes: Produce sperm (exocrine) and secrete testosterone (endocrine).
• Interstitial cells: Targeted by LH to secrete testosterone.
• Accessory glands contribute to seminal fluid: seminal vesicles, prostate gland, bulbourethral glands.
  • Seminal vesicles: Provide fructose, prostaglandins, and bicarbonate.
  • Prostate gland: Secretes milky fluid that activates sperm.
  • Bulbourethral gland: Produces alkaline mucus for lubrication.
• Spermatogenesis: Sperm formation, begins at puberty.

Gametogenesis

• Diploid chromosome number (2n): 46.
• Haploid chromosome number (n): 23.
• Spermatogenesis: Meiosis in males.
• Spermiogenesis: production of spermatids

Hormonal Control in Males

• GnRH from the hypothalamus stimulates the anterior pituitary to release FSH and LH.
• FSH stimulates spermatogonia to produce sperm.
• LH stimulates interstitial cells to release testosterone.
• Testosterone enhances spermatogenesis and promotes secondary sex characteristics.

Female Reproductive System

• Ovaries: Primary reproductive organ (gonad) in females.
• Oogenesis: Egg production.
• Females are born with about 2 million follicles, which decreases to 300,000–400,000 by puberty.

Oogenesis

• Oogonia: Stem cells.
• Primary oocyte: Arrested in meiosis I until ovulation.
• Secondary oocyte: Arrested in meiosis II until fertilization.
• Ovum: Mature oocyte, occurs only when fertilization finishes meiosis.

Ovarian Cycle

• Regulated by FSH and LH.
• Follicular phase: Follicle matures.
• Luteal phase: Corpus luteum forms.
• Ovarian cycle – 28-day cyclic changes within the ovaries
  • FSH and LH produce estrogen and progesterone.

Uterine Cycle

• Caused by estrogen and progesterone.
• Menstruation (Days 1–5): Endometrium disintegrates due to low hormone levels.
• Proliferative phase (Days 6–13): Endometrium thickens due to estrogen.
• Secretory phase (Days 15–28): Endometrium thickens and uterine glands mature due to progesterone.

Estrogen and Progesterone

• Responsible for secondary sex characteristics and breast development.
• Menopause: Ovarian cycle ceases, ovaries no longer respond to gonadotropic hormones.

Fertilization and Pregnancy

• Zygote: Fertilized egg.
• Embryo: Developing organism after mitosis.
• Implantation: Embryo implants in the endometrial lining.
• Only one sperm is needed to fertilize the egg, which is then called a zygote

Key Structures and Order

• Sperm travel: Seminiferous tubules → Rete testis → Epididymis → Ductus deferens → Ejaculatory duct → Prostatic urethra → Membranous urethra → Spongy urethra → External urethral orifice.
• Ovum travel: Ovary → Fimbriae of uterine tube → Infundibulum of uterine tube → Uterine tube → Uterus → Cervical canal → Vagina → Vaginal orifice.

Hormonal Effects

• Male
  • LH: Targets interstitial cells; stimulates testosterone secretion.
  • FSH: Targets seminiferous tubules; stimulates spermatogenesis.
  • Testosterone: Development/maintenance of sex organs, secondary sex characteristics, spermatogenesis
• Female
  • LH: Stimulates ovulation, formation of corpus luteum, progesterone secretion.
  • FSH: Stimulates follicle development, estrogen secretion.
  • Estrogen: Development/maintenance of sex organs, secondary sex characteristics, endometrial proliferation.
  • Progesterone: Prepares uterus for implantation, maintains pregnancy.