Final answer:
The three germ layers of the embryo are the ectoderm, mesoderm, and endoderm, which differentiate to form all tissues and organs in the body. The formation of these layers occurs during the second week after fertilization in a process known as gastrulation.
Step-by-step explanation:
The Three Layers of an Embryo
During embryogenesis, particularly in the second week after fertilization, the embryo develops three primary cell layers known as germ layers. These layers are pivotal as they differentiate to form all the tissues and organs of the body. The layers include the ectoderm, mesoderm, and endoderm.
The ectoderm is the outermost layer that gives rise to the epidermis, which includes the skin, and the nervous system, as well as other tissues like the eyes and inner ears. The mesoderm, the middle layer, develops into muscle cells, connective tissue, and organs such as the heart, blood, bones, and kidneys. Lastly, the endoderm is the innermost layer that forms internal organs and glands, including the lungs, intestines, thyroid, pancreas, and bladder.
This process of cell migration and differentiation is a fundamental aspect of the embryonic development, transforming the embryo from a two-layered disc to a three-layered structure via a process known as gastrulation. This transformation allows the cells to transition from totipotency, where a cell can form any type of cell, to multipotency, where they are limited to forming cells within a certain group of related cell types.