Embryogenesis is the process by which an embryo forms and grows in the uterus of a pregnant woman. The process of embryogenesis begins when an egg is fertilized by a sperm. After that, a massively complex sequence of events goes in motion. This process ultimately leads to the development of a baby!
Let’s take a look at some of the key points in embryogenesis. As is the case with most things in science and medicine, there are a lot of terms and name for each step in the process – it can get confusing.
When an egg combines with a sperm, the result is a single cell known as a zygote. This zygote contains genetic material from both the mother and the father. Chemical signals soon induce the zygote to split in to two cells. These divisions take place quickly – soon making the new embryo into a small multi-cellular organism. It is interesting to note that the early divisions of the zygote to not make the entire structure larger – instead each cell becomes a bit smaller.
Once there are enough cells in the newly formed structure, it becomes a blastula. Scientists typically call the new embryo a blastula when there are about 100 cells in total. Of course, this is a somewhat arbitrary distinction and has little meaning outside a lab or discussion with an embryologist.
From here, the process of development becomes very complex very quickly. There is no way to outline all of the subsequent steps in great detail. Entire books have been written about embryo development. In Medical School, embryology is a semester long class (which is rather more difficult that you’d expect).
In short, the blastula undergoes a process known as gastrulation (this only happens in mammals. The situation is different in plants and other types of animals). During gastrulation and subsequent development, all of the different tissues and organs differentiate themselves from the original cells (which are structurally identical).
The first step of gastrulation in mammals involves the formation of three layers of tissues. These layers are known as the ectoderm, endoderm, and mesoderm. Each of these three layers is the pre-cursor to a set of organs and tissues. For example, most of your skeletal muscles is formed from the mesodermal layer. Ectoderm goes on to become the nervous system. A complete list of all organ systems and their derivatives is very long and complex.
Ultimately, the cells from each of these three layers become part of the nervous system, the skeletal system, the renal system, and all of the other important structures that it takes to assemble a fully grown baby.
There is much, much more involved in the process of embryogenesis than is able to be outlined in this article. The growth and development of a baby from a fertilized egg is a complex process that involves a great deal of study to master. It is a fascinating process that seems like it shouldn’t be possible – yet it is!