Embryology Series Introduction Lecture

Overview

• The lecture series focuses on embryology, starting from the end of fertilization.
• It will cover the development during the first three weeks and the formation of the nervous system.

Uterine Anatomy Recap

• Vagina: Also known as the sheath.
• Cervix: The lower part of the uterus.
• Body of the Uterus: Main part of the uterus.
• Fundus: The top, rounded part of the uterus.
• Fallopian Tubes: Connects to the uterus, where fertilization occurs.
• Ampulla: Dilated region of the fallopian tubes, site for fertilization.
• Ovaries: Produce hormones and eggs.

Hormonal Physiology

• Around Day 14-15 of menstrual cycle, Luteinizing Hormone (LH) is released.
• Hypothalamus releases:
  • Gonadotropin-releasing hormone (GnRH).
  • GnRH stimulates the anterior pituitary to release LH.
• LH Function:
  • Stimulates ovary to produce fluid and pressurizes the follicle.
  • Triggers prostaglandins to dilate vessels and enzymes to break connective tissue.
  • Results in ovulation (release of the secondary oocyte).

Ovulation Process

• Secondary Oocyte:
  • Stuck in metaphase II until fertilization.
• Fertilization:
  • Sperm travels through the female reproductive tract to reach the ampulla.
  • Capacitation: Cleaning of the sperm's head to bind with ZP3 receptors.
  • Acrosomal Reaction: Enzymatic release from sperm to penetrate the egg.
  • Fusion of sperm and egg nuclei results in a zygote with 46 chromosomes (diploid).

Stages of Early Embryonic Development

1. Cleavage:
   • Zygote undergoes mitotic divisions.
   • Progression from 2-cell to 4-cell, to 8-cell stage, and eventually to the 16-cell stage.
2. Morula Formation:
   • A solid ball of cells with a hollow center.
   • Cells are termed blastomeres.
3. Blastulation:
   • Formation of the blastocyst.
   • Inner Cell Mass: Forms the embryo (embryoblast).
   • Outer Cell Mass: Forms the placenta structure (trophoblast).

Differentiation of Cell Masses

• Trophoblast:
  • Differentiates into cytotrophoblast and syncytiotrophoblast.
  • Involved in placenta formation.
• Embryoblast:
  • Forms the bilaminar disk, leading to the embryo.

Summary of Events in the First Week

1. Ovulation
2. Fertilization
3. Cleavage
4. Blastulation
5. Differentiation into trophoblast and embryoblast.
6. Begin formation of bilaminar disk and further embryonic structures.

Next Steps

• The next video will explore further differentiation and the formation of the placenta and bilaminar disk.