Let’s take a trip back in time, to when you were just made up of a single cell. The sperm from your father and the egg from your mother will have just fused, forming a single-celled zygote. This zygote is now going to keep multiplying to form many cells, marking the start of embryonic development.
At some point, this mass of cells, making up the early embryo, will have implanted in your mother’s womb and begun to grow bigger. The cells will also have started to differentiate, transforming into all the different kinds of cells that make up who we are – skin, muscles, nerves, etc. Over time, the cells will also have developed into heart, lungs, the brain, and so forth. Finally, a whole nine months later, you will have been born, as a fully formed human baby.
In the early stages of the human embryo, before it has implanted in the mother’s womb, the cells arrange themselves in a particular way. A blob of cells gathers towards one side of the embryo and the other cells arrange themselves around this blob. This blob is called the inner cell mass. It contains cells with the ability to make all the other types of cells in the human body – i.e. the cells in this blob are pluripotent. Since a whole human body takes shape from this blob, scientists are naturally very interested in studying it in detail.
