This lecture covers the phases of the female reproductive cycle, focusing on the role of hormones like estrogen and progesterone.
It's essential to understand the ovulatory cycle as a prerequisite.
Hormones Involved
Estrogen: Produced by the ovaries; plays a crucial role in regenerating the uterine lining.
Progesterone: Produced by the corpus luteum post-ovulation; thickens the uterine lining and prepares it for potential pregnancy.
Phases of the Menstrual Cycle
1. Menstruation Phase
Duration: Days 1-5 on average.
Description: Shedding of the stratum functionalis of the endometrium.
Stratum Functionalis: The outer layer that is shed during menstruation. Contains spiral/coiled arteries.
Stratum Basalis: The inner layer that remains; contains straight arteries.
Blood Loss: Due to the rupture of spiral/coiled arteries as the stratum functionalis is shed.
2. Proliferative Phase
Duration: Days 6-14.
Key Hormone: Estrogen.
Activities:
Regeneration of the stratum functionalis.
Angiogenesis: Formation of new spiral/coiled arteries.
Uterine Glands: Formation begins; they do not secrete yet.
Cervical Mucus: Estrogen causes production of thin mucus to facilitate sperm movement during ovulation.
3. Secretory Phase
Duration: Days 15-28.
Key Hormone: Progesterone, produced by the corpus luteum.
Activities:
Further thickening of the stratum functionalis.
Angiogenesis continues, enhancing blood supply.
Uterine Glands: Begin to secrete a nutrient-rich fluid with glycogen, lipids, and proteins.
Cervical Mucus: Progesterone causes a thick plug to form, protecting the uterine environment.
Importance and Outcomes
Fertilization: If the egg is fertilized, human chorionic gonadotropin (hCG) maintains the corpus luteum secretion of progesterone.
No Fertilization: Corpus luteum degenerates into corpus albicans; progesterone levels drop, leading to the breakdown of the stratum functionalis and the start of menstruation.
Cycle Duration
Average menstrual cycle: 28 days.
Pathological if <21 days or >40 days.
Conclusion
Understanding these phases helps in comprehending how hormonal changes drive the menstrual cycle and prepare the female body for potential pregnancy.
Next steps include reviewing a summary to solidify this understanding.