PATHOLOGY

Detailed explanation-1: -Embryonic stem cells. These stem cells come from embryos that are 3 to 5 days old. At this stage, an embryo is called a blastocyst and has about 150 cells. These are pluripotent (ploo-RIP-uh-tunt) stem cells, meaning they can divide into more stem cells or can become any type of cell in the body.

Detailed explanation-2: -Embryonic stem cells (ESCs) are found in the inner cell mass of the human blastocyst, an early stage of the developing embryo lasting from the 4th to 7th day after fertilization. In normal embryonic development, they disappear after the 7th day, and begin to form the three embryonic tissue layers.

Detailed explanation-3: -A very specific and important event occurs after 5–6 days: the blastocyst changes very subtly and the cells in the inner cell mass lose the ability to read all of their DNA. In other words, cells are no longer pluripotent after this point in development.

Detailed explanation-4: -Researchers harvest the embryo stem cell at the Day 4 or 5 stage. This time frame is crucial, because it is just after the embryo begins dividing multiple cells within itself, but before those cells begin to differentiate.