Female Reproductive Cycle Overview

Key Cycles

• Ovarian Cycle and Menstrual Cycle
  • Ovarian involves hormones and ovaries
  • Menstrual involves changes in the uterus

Ovarian Cycle Phases

1. Follicular Phase (Day 1 - 13)
   • Development of the ovarian follicles
2. Ovulation Phase (Day 14)
   • Release of the ovum from the ovary
3. Luteal Phase (Post Ovulation)
   • Formation of the corpus luteum

Menstrual Cycle Phases

1. Menstrual Phase (Day 1 - 7)
   • Shedding of the uterine lining
2. Proliferative Phase (Day 5 - 14)
   • Regrowth of the uterine lining
3. Secretory Phase (Day 15 - 28)
   • Preparation of the uterine lining for potential implantation

Urogenesis and Follicular Development

• Primordial follicles present at birth, arrested in prophase 1.
• Develop into primary and secondary follicles during puberty.
• Selection process results in Graafian follicles responsive to FSH and LH.

Hormonal Regulation

• Estrogen and Progesterone
  • Low levels trigger menstruation.
• Hypothalamic-Pituitary-Gonadal (HPG) Axis
  • GNRH stimulates LH and FSH production.
  • Estrogen initially provides negative feedback, switches to positive feedback at high concentrations leading to LH and FSH surge.

Hormonal Phases

• Day 1 - Start of Menstruation
  • Low estrogen and progesterone levels.
  • Decreased negative feedback increases GNRH, LH, and FSH.
• Pre-Ovulation (Day 14)
  • Estrogen levels rise from developing follicles.
  • Positive feedback causes LH surge, leading to ovulation.
• Post-Ovulation
  • Corpus luteum forms, releasing progesterone.
  • Maintains negative feedback to prevent additional ovulation.

Fertilization and Pregnancy

• Without Fertilization: Estrogen and progesterone levels drop, cycle restarts.
• With Fertilization:
  • Zygote forms, producing HCG.
  • HCG functions like progesterone, maintaining the uterine lining.

Key Concepts for MCAT

• Understand hormone pathways.
• Estrogen as a steroid hormone crossing membranes to regulate gene expression.
• Mechanisms of feedback in hormonal regulation.

Additional Resources

• For deeper understanding, explore videos on the endocrine system and genetics.