Overview
This lecture introduces oogenesis, the process of egg cell formation in the ovary, describing the involved structures, key hormone roles, and differences from spermatogenesis.
Structures in the Ovary
- Oogenesis occurs inside the ovary, the site for egg cell production.
- Primordial follicles are undifferentiated cells that can develop into egg cells.
- As follicles mature, they grow larger and become Graafian follicles.
- The Graafian follicle contains the oocyte (immature egg cell).
- After ovulation, the empty Graafian follicle becomes the corpus luteum, which later shrinks and disappears.
Hormonal Control of Oogenesis
- Follicle Stimulating Hormone (FSH), produced by the pituitary gland, stimulates follicle growth in the ovary.
- Luteinizing Hormone (LH), also from the pituitary, triggers ovulation (release of the ovum).
- Ovulation occurs around day 14 of the ovarian cycle.
- The corpus luteum secretes progesterone, a hormone that prepares the uterus for possible pregnancy.
- If fertilization does not occur, progesterone levels drop as the corpus luteum disintegrates, restarting the cycle.
Egg Cell Structure
- The ovum has a nucleus (haploid, n), nucleolus, abundant cytoplasm, and a plasma membrane.
- Zona pellucida is a dense, protective jelly-like layer around the ovum where sperm may get trapped.
Oogenesis vs Spermatogenesis
- Both start with diploid precursor cells and involve meiotic cell divisions.
- Spermatogenesis usually produces four equal haploid sperm cells.
- Oogenesis creates one large ovum and three smaller polar bodies (which degenerate).
- Most cytoplasm is retained in the single egg cell to support potential embryonic development.
Key Terms & Definitions
- Oogenesis — production of egg cells via meiosis, forming one mature ovum and polar bodies.
- Follicle — developing structure in the ovary containing the immature oocyte.
- Graafian follicle — fully matured follicle containing the oocyte ready for ovulation.
- Corpus luteum — remnant of the Graafian follicle after ovulation; secretes progesterone.
- FSH (Follicle Stimulating Hormone) — hormone that stimulates follicle growth.
- LH (Luteinizing Hormone) — hormone that triggers ovulation.
- Progesterone — hormone secreted by corpus luteum to maintain pregnancy.
- Polar body — small cell produced during oogenesis that does not become an ovum.
- Oocyte/Ovum — egg cell at various developmental stages.
- Zona pellucida — protective outer jelly layer of the egg cell.
Action Items / Next Steps
- Watch the upcoming lecture on the menstrual cycle and hormone interactions for more detailed understanding.
- Practice labeling diagrams of the ovarian cycle and follicle stages.