Lecture on Ovarian and Uterine Cycles

Overview

• The ovarian cycle is roughly 28 days and includes the follicular phase and the luteal phase.
• Ovulation marks the transition between these phases.
• Variability in cycle length is mostly due to the follicular phase.

Follicular Phase

• Follicles develop from primordial to primary, then to secondary and eventually to vesicular follicles.
  • Primordial Follicle: Thin cells surrounding a primary oocyte.
  • Primary Follicle: Cells bulk up and oocyte enlarges.
  • Secondary Follicle: Follicular cells stratify to become granulosa cells.
  • Vesicular Follicle: Granulosa and connective tissues form theca cells; oocyte secretes zona pellucida.
  • Fluid-filled antrum forms, leading to the mature vesicular follicle.
• Dominant follicle selected mid-phase due to declining FSH.
• Dominant follicle's oocyte completes meiosis I.

Luteal Phase

• Post-ovulation, the follicle becomes the corpus luteum.
• Corpus luteum secretes hormones like progesterone and estrogen.
• Without implantation, corpus luteum degenerates leading to the ischemic phase.

Hormonal Regulation

• Follicle Stimulating Hormone (FSH): Stimulates follicle growth.
• Luteinizing Hormone (LH): Triggers ovulation.
• Estrogens and Progesterone: Produced by granulosa and theca cells; regulate cycle.
• Inhibin feedback reduces FSH to allow dominant follicle selection.

Ovulation

• LH surge causes rupture of vesicular follicle, releasing secondary oocyte.
• Ovulation pain (mittelschmerz) may occur.
• Possible multiple oocyte release can cause fraternal multiples.

Uterine Cycle

• Menstrual Phase: Shedding of stratum functionalis.
• Proliferative Phase: Regeneration of the endometrium.
• Secretory Phase: Endometrial thickening, increased progesterone secretion.

Pre-puberty and Puberty

• Ovaries secrete low levels of estrogens; negative feedback inhibits further hormone release.
• At puberty, GnRH stimulates FSH and LH release leading to menarche.

Pregnancy and Implantation

• Corpus luteum supports early pregnancy if fertilization occurs.
• If not, it degenerates, allowing the cycle to restart.

Embryonic Development

• Amniotic Egg Components:
  • Yolk Sac: Nutrient provider.
  • Allantois: Waste storage.
  • Amnion: Shock absorption.
  • Chorion: Gas exchange.
• Placental mammals use the umbilical cord and placenta for fetal development.

Conclusion

• Understanding of the ovarian and uterine cycles is crucial for reproductive health.
• The coordination of hormones is essential for the cyclic nature of female reproduction.

These notes cover the primary concepts of ovarian and uterine physiology and their hormonal regulation as discussed in the lecture.