A blastocyst is a structure that forms during the early stages of embryonic development in mammals. It is formed from a fertilized egg and undergoes several stages of cell division to form a hollow sphere of cells. The blastocyst is composed of two distinct cell populations: the inner cell mass (ICM) and the trophoblast.
The inner cell mass is a cluster of cells that will ultimately give rise to the embryo itself. The cells within the ICM are pluripotent, which means that they have the ability to differentiate into any type of cell in the body. These cells will later form the various tissues and organs of the developing fetus.
The trophoblast is the outer layer of cells that surrounds the inner cell mass. These cells are responsible for implanting the blastocyst into the uterine wall and eventually give rise to the placenta and other supporting tissues needed for fetal development within the uterus.
Between the inner cell mass and the blastocyst cavity lies a thin layer of cells called the hypoblast. These cells will contribute to the formation of the embryonic endoderm, which will give rise to the respiratory and digestive tracts of the developing fetus.
Overall, the blastocyst stage is a crucial point in embryonic development, as it marks the beginning of the formation of the embryo and the supporting structures needed for fetal development.