Fetal Membranes

Blastocyst and Embryo Development

• The extraembryonic structures developed from the blastocyst do not contribute to the embryo itself include the yolk sac and the amnion.
• The trophoblast layer of the blastocyst is composed of two parts: cytotrophoblast (inner layer) and syncytiotrophoblast (outer layer).

Functions of Extraembryonic Structures

• The yolk sac provides early nourishment to the developing embryo and plays a role in the formation of blood cells before the establishment of the placenta.
• The allantois is involved in waste removal and gas exchange; it contributes to the formation of the umbilical cord and plays a role in the development of the urinary bladder.

Formation and Embedding Processes

• The fetal part of the placenta is formed by the trophoblast layer, particularly the syncytiotrophoblast, which invades the maternal tissue.
• The blastocyst begins to partially embed into the endometrial stroma typically around day 6 after fertilization.

Yolk Sac Stalk

• The yolk sac stalk, also known as the vitelline duct, eventually regresses and may leave behind remnants, but its primary function diminishes as the placenta takes over nutritional support.

Test your knowledge of the components, development, fate, and functions of fetal membranes with this quiz. Explore the correlation between fetal membrane importance and pregnancy, as well as anomalies related to fetal membranes. Topics include amnion, yolk sac, and their roles in fetal growth and development.