Meaning of Embryonic Development

This article was last modified on: September 24th, 2019

What is Embryonic Development:

Embryonic Development is the study of embryology on the development of an individual from the process of their fertilization and formation of the zygote (egg cell), to the constitution of their organs, bones, tissues and other parts of the body during a pregnancy.

The stages of embryonic development

Within the process of forming an individual, there are several important stages that define its development. These processes begin by fertilizing and fertilizing two gametes: the female and the male, which become one cell: the zygote .

From its fertilization, the originated cell goes through some important phases that determine its DNA, in addition to the development of organs and other parts of the body.

The functions of sperm and egg in the processes of fertilization and fertilization

The male gamete, known as sperm (or SPTZ), has a haploid pronucleus, ie, has only one set of genetic material, responsible for the formation of the embryo. This genetic set is called a chromosome .

Structure of a sperm: male gamete
Structure of a sperm: male gamete

The female gamete, known as the secondaryoocyte , is also haploid and carries the other half of the genetic material responsible for embryo formation.

Microscopic view of a secondary egg, the female gamete, surrounded by sperm.
Microscopic view of a secondary egg, the female gamete, surrounded by sperm.

The formation of the Zygote

Upon entering the vaginal canal, sperm can fertilize (or fuse) the secondary oocyte. This act of fertilization is called cariogamy , that is: the union of female and male gametes.

But for the emergence of the embryo to happen, egg fertilization is required. Then, after the sperm fuses into the secondary egg, the fertilization process occurs: the union of the female pronucleus with the male pronucleus, which happens in the fallopian tube near the ovaries.

Through this fertilization arises the zygote (or egg cell): a diploid cell, with both genetic materials provided by the male and female pronuclei.

Zygote cell in fertilization process between male and female pronuclei.
Zygote cell in fertilization process between male and female pronuclei.

Know the particularities of the Zygote cell and learn more about Fertilization.

Cleavage and Morula

Already with the genetic material of the two gametes, the zygote enters the process of Cleavage (or Segmentation), built through mitosis , where the embryo cytoplasms are divided on a large scale, forming small nucleated and identical cells called blastomers .

Cleavage phase, where the zygote suffers mitosis.
Cleavage phase, where the zygote suffers mitosis.

At the end of the Cleavage, the Morula phase occurs : the first stage of embryogenesis or the first relevant stage of embryonic development. In this stage a massive material is formed, with 12 to 32 blastomers, containing all the individual’s DNA.

The morula occurs three to four days after fertilization and is responsible for bringing the embryo into the uterus, initiating the phase of the blastula .

See more about the meaning of Mitosis and DNA.

The Blastula phase

Here begins a change in cell structure. Blastomers begin to migrate to the periphery, giving rise to a cell wall called blastoderm, forming an internal cavity called blastocele within the massive material formed in the Morula phase.

Blastomers migrating to the periphery and forming the blastocele cavity
Blastomers migrating to the periphery and forming the blastocele cavity

The blastula is considered the second stage of embryogenesis, where the embryo undergoes the process of nesting , settling once and for all in the womb.

After the formation of the blastula and the nesting process, the blastocele goes through the process of invagination or epibolism , forming a new cavity called Archenter . This cavity is also responsible for forming the digestive tract, initiating the phase of the Gastrula.

Gastric Formation: endoderm invagination process.
Gastric Formation: endoderm invagination process.

Understand more about the Nesting process.

The gastrula phase

In this third stage of embryogenesis, the open space in the archenterus, called the blastopore , is responsible for giving rise to one end of the digestive tract: the mouth (protostomy) or the anus (deuterostomy).

It is also at this stage that we find the three different cell layers (or germ leaflets), where each is responsible for distinct functions in embryo development:

  • The ectoderm : outer layer, responsible for forming the archenterus;
  • The mesentoderm : originates the endoderm (outer surface of the gastrula that produces the skin and the central nervous system of the being) and the mesoderm (formed by the mesenchymal cells, which will give rise to other
Example of germinal leaflets
Example of germinal leaflets

The Neurulation Phase (Neurula)

In this phase the morphogenesis begins, that is, the embryo begins to take the form of the baby. Here the ectoderm, mesoderm, and endoderm cell tissues attach to and originate histogenesis and organogenesis , processes where cellular tissues begin to form organs, bones, and other parts of the body.

In the Neurulation phase are:

  • neural tube: responsible for giving rise to the nervous system of the individual;
  • Celoma: structure that originates the thoracic and abdominal cavity;
  • notochord: support axis found in the embryo, only in chordate animals (fish, amphibians, reptiles, birds and mammals). The notochord serves as a template for the spine, calcifying and being and replaced by the spine after a few months of gestation;
  • archenter: originates the digestive tract.

Embryonic Attachment Formation

During the formation of the germ leaflets (ectoderm, endoderm and mesoderm) and in the nesting process, embryonic annexes arise: structures that are born from the outer cell layers and that play important roles in pregnancy, such as:

  • Ammonium : Liquid present inside the amniotic sac, which protects the embryo from impacts and does not allow the dehydration of the fetus;
  • vitelline sac : structure that serves to nourish the embryo and assists the blood circulation in early pregnancy;
  • Chorium : directly attached to the uterine tissue, is responsible for forming the placenta.

Problems in the Neurulation Phase: Neural Diseases

The neurulation phase is of utmost importance, especially in the formation of the nervous system of the being. Therefore, when some of the processes, such as invagination, are not completed at this stage, it can cause organ malformation.

Some diseases such as anencephaly , encephalocele or myelomeningocele , are examples of the result of errors in neural tube processes.

Anencephaly, for example, is caused by not closing the neural tube. When this happens, the fetus does not fully develop the organs of the brain and cranial box, which consequently are exposed to amniotic fluid, further aggravating the problems of the embryo’s nervous system.

Stem cells

In the first relevant stage of embryology ( the morula ), the cells (blastomers) are multiplying, but have no definition of what they will create within pregnancy.

Because they do not have a specificity of their role within embryonic development, they are called stem cells .

These embryonic stem cells are periodically used in research, being analyzed for testing and possible cures for numerous diseases, such as cancer.

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