Blastocyst

Common card · No. 263578

The blastocyst is formed in the early embryonic development of mammals. It possesses an inner cell mass (ICM) also known as the embryoblast which subsequently forms the embryo, and an outer layer of epithelial cells called the trophectoderm. This layer surrounding the inner cell mass is responsible for the formation of the fluid-filled cavity or lumen known as the blastocoel. In the late blastocyst, the trophectoderm changes to trophoblast. The trophoblast gives rise to the chorion and amnion, the two fetal membranes that surround the embryo. The placenta derives from the embryonic chorion (the portion of the chorion that develops villi). The corresponding structure in non-mammalian animals is an undifferentiated ball of cells called the blastula. In humans, blastocyst formation begins about five days after fertilization when a fluid-filled cavity opens up in the morula, the early embryonic stage of a ball of 16 cells. The blastocyst has a diameter of about 0.1–0.2 mm and comprises 100...

Read on Wikipedia · Image Zachary Wilson / CK-12 Foundation, CC BY-SA 3.0