Final answer:
Human embryonic stem cells, initially totipotent, have the potential to differentiate into any cell type. They form three germ layers during development, which then specialize into all tissues and organs in the body.
Step-by-step explanation:
Human embryonic stem cells are the building blocks of life. Early in pregnancy, they begin to differentiate into all the body's specialized tissues and organs. The inner mass of these embryonic cells is totipotent during the early stages, meaning each cell has the potential to become any cell type in the human body. This totipotency lasts only a few days before the cells begin to commit to specific lineages as precursors to distinct germ layers: the ectoderm, mesoderm, and endoderm.
After the totipotent stage, the cells become pluripotent, having the potential to differentiate into any type of human tissue but not able to support the full development of an organism. As development proceeds, these cells become multipotent, with the ability to differentiate into a narrower range of cell types.
During embryogenesis, the rapid mitotic cycles of the fertilized egg, or zygote, produce a growing number of cells that form the embryo. These cells soon arrange into the three primary tissue layers, with each layer destined to form different tissues and organs in the body. For example, the ectoderm develops into the nervous system, while the mesoderm forms muscle tissue, among others.
The process of differentiation is crucial as it determines the specialized structures and functions of the cells, leading to the complex organism made up of trillions of specialized cells you see today.