Lecture Notes: Endometrium and Hormonal Regulation in Female Reproductive System

Endometrium Structure

• Two Layers of the Endometrium
  • Stratum Functionalis
    • Grows each month.
    • Sheds if pregnancy does not occur.
  • Stratum Basalis
    • Provides the foundation for the regeneration of stratum functionalis.

Menstrual Cycle and Hormonal Influence

• Progesterone Levels
  • Low levels lead to constriction of spiral arteries.
  • Causes stratum functionalis to slough off, leading to menstruation.
• Role in Pregnancy
  • High progesterone levels maintain the stratum functionalis, allowing for implantation.

Implantation and Early Pregnancy

• Embryo Contribution
  • Trophoblast releases digestive enzymes.
  • Facilitates embryo embedding into the stratum functionalis.
  • Development of yolk sac and chorion.
  • Chorionic villi aid in maternal-fetal exchange.
• Placenta Formation
  • Combination of embryonic and maternal contributions.

Hormones and Their Actions

• Estrogen
  • Development of secondary sex characteristics.
  • Egg and endometrium development.
  • Regulates cholesterol levels.
• Progesterone
  • Maintains uterine lining.
  • Involved in milk production.
  • Decrease triggers menstruation.
• Luteinizing Hormone (LH)
  • Stimulates ovulation.
• Follicle Stimulating Hormone (FSH)
  • Stimulates follicle and oocyte maturation.
• Human Chorionic Gonadotropin (hCG)
  • Maintains corpus luteum hormone secretion.
• Relaxin
  • Relaxes uterine wall and pubic symphysis.
• Inhibin
  • Inhibits FSH to prevent new follicle development during pregnancy.
• Prolactin
  • Aids in milk production (with progesterone).
• Oxytocin
  • Facilitates labor contractions and milk ejection.

Understanding Gestation

• Duration
  • From fertilization to birth (~38 weeks).
  • Embryonic period is first 8 weeks, focusing on organ development.

Additional Notes

• Hormones such as prolactin and oxytocin function through positive feedback, while others utilize negative feedback mechanisms.
• A significant proportion of embryos do not implant or survive early stages, underlining the complexity of the reproductive process.