Embryogenesis begins with fertilization and lasts eight weeks.
Embryogenesis is the process that, starting from a zygote , allows the creation of a multicellular organism . Embryogenesis begins when the gametes are fertilized and the embryo emerges.
human embryogenesis
In human embryogenesis , embryo development takes about eight weeks. In this period, the product of conception completes its initial stage of development; From then on, it becomes known as a fetus .
Embryogenesis assumes that a set of cells make up the embryo itself, while another group enables the formation of the embryonic annexes (the chorion and the amnion ). Already in the initial weeks, future organs begin to form in the embryo.
Between the embryonic annexes and the embryo appears the placenta , which is linked to the embryo through the umbilical cord . This cord serves to eliminate waste and transport nutrients and oxygen to the embryo.
From fertilization to the fetus
Embryogenesis begins at fertilization and ends when the embryo is called "fetus." This first step, which is also known as impregnation or conception , involves the sperm joining the female gamete: the internal structures of the former enter the cytoplasm of the latter. Four hours after this moment, the DNA of each part becomes organized into pronuclei, which have half the chromosomes of a normal cell, that is, of any other cell. Two hours later, the pronuclei approach and DNA begins to be synthesized inside.
When the pronuclei reach their maximum dimensions, the moment of cell division arrives and the zygote emerges, the cell that results from the union of both gametes . It is a single cell embryo. Only at the end of the first day does a bicellular one emerge, and its division continues until on the fifth day it becomes called a blastocyst . From the second week of embryogenesis, the blastocyst buries itself in the endometrium of the uterus . At this point the so-called lacunar phase takes place, whose name refers to gaps that form between the cells.
Another milestone takes place in the fourth week, when the development of the spaces where the organs will later be located arises, although in a preliminary way, and the embryonic disc folds and the embryo takes on an appearance more similar to that of a vertebrate organism . It is a turning point, from which growth accelerates considerably.
The following four weeks of embryogenesis are known as the embryonic period . It is then that organs and tissues are formed from the three embryonic leaves . One of them is called mesoderm , and is responsible for the formation of various structures: the chordate forms the notochord, an organ that, for example, participates in the development of the neural tube; the somitic , the somites, responsible for the skeleton and muscle, among other parts; the intermediate , the gonads and the excretory system; the latero-ventral , the circulatory system; the prechordal , the mesenchyme of the face.
When embryogenesis is completed, the bastocyst is called "fetus."
Phases of embryogenesis
It is possible to recognize four phases in embryogenesis that, in vertebrate animals, develop sequentially. Segmentation takes place first, which involves the division of the zygote through mitosis . Thus the embryo becomes a blastocyst .
Then come gastrulation , neurulation and organogenesis . At each step, the embryo gains complexity and advances in its progression.
plant embryogenesis
Regarding plant embryogenesis , these are those processes that cause the zygote to transform into the embryo, which is located in the mature seed . All stages make it possible for the embryo to become autotrophic once the different stages are completed.