Overview
This lecture covers the process of oogenesis in the female reproductive cycle, emphasizing the development and maturation of eggs (oocytes) and the associated hormonal and cellular changes.
The Female Reproductive Cycle
- The female reproductive cycle refers to the monthly maturation of eggs (oocytes) in the ovaries.
- All eggs are created during fetal development and remain inactive until puberty.
- At puberty, one egg matures each month, becoming available for fertilization.
Stages of Egg Development (Oogenesis)
- Oogenesis is the process of egg development in the ovaries.
- Precursor germ cells (oogonia) undergo mitosis during fetal development, creating about 2–4 million cells.
- Oogonia develop into primary oocytes before birth and become arrested in meiosis I (meiotic arrest).
- At puberty, some primary oocytes resume meiosis I, leading to ovulation.
- Most primary oocytes remain in meiotic arrest and eventually die without maturing.
Meiosis and Ovulation
- Meiosis reduces the chromosome number in germ cells.
- Upon ovulation, the primary oocyte completes meiosis I, creating a large secondary oocyte and a small polar body.
- The secondary oocyte is released during ovulation and can be fertilized by sperm.
- Meiosis II is only completed if the secondary oocyte is fertilized by sperm, producing another polar body.
- After fertilization and completion of meiosis II, the cell is called an ovum, and once nuclei fuse, it becomes a zygote.
- If fertilization does not occur, the oocyte is shed during menstruation as a secondary oocyte.
Ovarian Hormones
- The ovaries secrete estrogen, progesterone, and inhibin, which regulate the reproductive cycle.
Key Terms & Definitions
- Oogenesis — the process of egg (oocyte) development.
- Oogonia — germ cell precursors to oocytes.
- Primary oocyte — an egg cell arrested in meiosis I.
- Meiotic arrest — the halting of meiosis in primary oocytes until puberty.
- Secondary oocyte — the matured egg released during ovulation.
- Polar body — a small cell produced during meiosis that typically degenerates.
- Ovum — a fertilized secondary oocyte.
- Zygote — a cell formed by fusion of sperm and ovum.
Action Items / Next Steps
- Review the stages of oogenesis and ovulation.
- Study the hormonal regulation of the female reproductive cycle.