Question

Describe the process embryonic development. Consider the following:

a. What milestones/steps are included in this process and when do they occur?

b. What structures are formed as the embryo develops?

c. How do the structures identified in part “b” contribute to embryonic development? ~Part "b" refers to the answer to part b, not a diagram.

Answer 1

Embryonic development also embryogenesis is the process by which the embryo forms and develops.Three major events occur during the embryonic stage: implantation, the division of germ layers, and organogenesis.

Implantation :

Conception and fertilization are terms for the moment when the sperm fertilizes the egg. This occurs at some point following the egg's release from an ovary, on its journey to the uterus. Even from the moment of joining, changes are happening and the cells begin to split time and time again, as the now multi-cell clump continues on its journey to the womb.

In order for development to continue, a connection must be formed between the mother and the embryo. Upon arrival to the uterus, the rapidly-changing embryo implants, or burrows, into the uterine lining. In human development, implantation happens 5-10 days after conception in almost all cases.

After fertilization but before implantation, an embryo is surrounded by its trophectoderm. The trophectoderm, or trophoblast, is a special layer of cells that covers the outside of an embryo and supplies the ball of cells with nutrition. Once implantation has occurred, this trophectoderm changes in significant ways. The trophectoderm begins to differentiate into supporting structures such as the placenta so that the embryo can now receive nutrition and oxygen from the mother's blood supply.

It is estimated that only half of fertilized eggs successfully implant in the uterine wall; when implantation fails, the pregnancy ends without the mother even knowing it had occurred in the first place.

Division of Germ Layer :

A germ layer is a collection of cells that determine which cells within the embryo will eventually develop into particular organs and tissues.

There are three germ layers: ectoderm, mesoderm, and endoderm. The ectoderm, towards the outer surface of the embryo, will eventually become the nervous system, skin, and sensory organs such as the ears and eye. Similarly, the mesoderm, just inside the outer-most ectoderm of the embryo, becomes the skeleton, muscles, circulatory system, and the genitalia. The endoderm, at the core of the embryo, becomes the most inner organs such as the gastrointestinal system and the lungs as well as the pancreas and liver.

Organogenesis:

Organogenesis is the phase of embryonic development that starts at the end of gastrulation and continues until birth. During organogenesis, the three germ layers formed from gastrulation (the ectoderm, endoderm, and mesoderm) form the internal organs of the organism.

In vertebrates, one of the primary steps during organogenesis is the formation of the neural system. The ectoderm forms epithelial cells and tissues, as well as neuronal tissues. During the formation of the neural system, special signaling molecules called growth factors signal some cells at the edge of the ectoderm to become epidermis cells. The remaining cells in the center form the neural plate. If the signaling by growth factors were disrupted, then the entire ectoderm would differentiate into neural tissue. The neural plate undergoes a series of cell movements where it rolls up and forms a tube called the neural tube. In further development, the neural tube will give rise to the brain and the spinal cord.