Female Reproductive Cycle

Overview

• Reproductive Cycle: Refers to the maturation of eggs within the ovaries.
• Oogenesis: Process of egg creation in the ovaries during gestation.
• Oocyte: Another term for egg.

Egg Development

• Gestation: Eggs are created in the ovaries while a female fetus is in utero.
  • Eggs remain inactive until puberty.
• Puberty: Reproductive cycle begins; one egg matures monthly for potential fertilization.

Ovulation

• Process: Mature egg is released from the ovary.
• Hormones: Ovaries secrete estrogen, progesterone, and inhibin.

Formation of Eggs

• Early Development:
  • Oogonia: Precursor germ cells undergo mitotic divisions to increase in number.
  • By the 7th month, mitotic division stops; 2-4 million oogonia are produced.
  • Oogonia develop into primary oocytes.
• Chromosome Level:
  • Oogonia and primary oocytes are diploid (2n).
  • Primary oocytes begin meiosis 1 but halt midway, entering meiotic arrest.

Meiotic Arrest

• Primary Oocytes: Remain in meiotic arrest when the female is born.
• Development Post-Puberty:
  • Some oocytes resume development, complete meiosis 1, and become secondary oocytes.
  • Many primary oocytes die.

Secondary Oocyte Development

• Meiosis 1 Completion: One cell gets most of the cytoplasm, becomes a secondary oocyte.
  • Polar Body: The other cell withers and dies.
• Ovulation: Secondary oocyte is released.

Fertilization and Meiosis 2

• Fertilization: Occurs in the uterine tubes.
• Meiosis 2: Final meiosis step occurs when sperm fuses with secondary oocyte.
  • Results in formation of a second polar body.
  • Oocyte becomes an ovum (only if fertilized).
• Zygote Formation: Fusion of sperm and egg nuclei.

Non-Fertilization

• Secondary Oocyte: If not fertilized, it is expelled during menstruation, not as an ovum.