Blastocyst: A thin-walled hollow structure in early embryonic development that contains a cluster of cells called the inner cell mass from which the embryo arises. The outer layer of cells gives rise to the placenta and other supporting tissues needed for fetal development within the uterus while the inner cell mass cells gives rise to the tissues of the body.
Quick GuideUnderstanding Cancer: Metastasis, Stages of Cancer, and More
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Last Editorial Review: 5/13/2016