A blastocyst is a thin walled hollow structure formed in the early development of mammals. It possesses cluster of cells called an inner cell mass (ICM) which subsequently forms the embryo. The outer layer of the blastocyst consists of cells collectively called the trophoblastic.
It forms to placenta and other supporting tissue needed for foetal development within the uterus while the inner cellular mass cells gives rise to the tissue of the body. There is a thin layer of cells in blastocyst between the inner cellular mass and cavity known as hypoblast. These cells contribute to the formation of embryonic endoderm which will make respiratory and digestive track of baby.