Summary
Highlights
During embryological development, four extraembryonic membranes are formed: the chorion, amnion, allantois, and umbilical vesicle (yolk sac in other animals). These membranes are discarded after birth. This lecture focuses on their roles in human embryo development.
The chorion is the outermost extraembryonic membrane, enclosing the embryo and the other membranes. It's formed from trophoblast cells and mesoderm. The chorion produces chorionic fluid, which fills the chorionic cavity and protects the embryo from shock. It also forms chorionic extensions that connect with maternal blood vessels, developing into the placenta for nutrient, oxygen, and waste exchange.
The amnion directly surrounds the developing embryo and consists of mesoderm and ectoderm layers. It produces amniotic fluid within the amniotic cavity, which cushions the fetus, prevents it from drying out, and allows freedom of movement.
In humans, the yolk sac is called the umbilical vesicle, as it doesn't contain yolk. In early development, it helps produce red blood cells for the fetus.
In non-human animals, the allantois is crucial for waste disposal. In humans, it's a small outgrowth of the developing digestive tract, primarily contributing to the formation of blood vessels within the umbilical cord.
The four extraembryonic membranes—chorion, amnion, umbilical vesicle, and allantois—are vital for embryonic development and are eventually discarded after birth.