24 hours after the union between the Ovum and the spermatozoon, the second stage of pregnancy begins, also called the embryonic period. During this crucial moment, the creation and development of the embryo takes place. This period is characterized by the passage of the embryo through different phases until it becomes the fetus.
Stages of embryonic development
Throughout embryonic development, the embryo goes through several stages, starting from a single cell to forming a complex structure. These stages include the morula, the blastocyst, and finally the embryo before entering the fetal state.
First phase: Morula
During the first five days, when the two cells that form the embryo begin to divide rapidly, the phase known as morulaThese divisions are rapid and each cell, known as a blastomere, divides again and again, creating a small ball of cells that resembles the shape of a blackberry, hence its name. Individual cells cannot yet be clearly distinguished due to their rapid proliferation.
Second phase: Blastocyst
Around the fifth or sixth day, the embryo enters a stage known as blastula or blastocyst. At this stage, the embryo takes on a more defined shape and an internal cavity is created. This cavity will be key to the formation of the placenta and the fetus in the future. The external structure of the blastocyst contains a layer of cells called trophoblast, which will later give rise to the placenta.
Implantation and formation of the embryo
The process of implantation of the blastocyst in the uterus is essential for the success of the pregnancy. During the first days of the blastocyst phase, the embryo must adhere to the lining of the uterus in order to be properly nourished and continue its development. This process ends approximately 14 days after the fertilization, when the embryo has managed to completely implant itself in the endometrium, the tissue that lines the uterus.
From embryo to fetus
Once the embryo has implanted, its development progresses rapidly. At this crucial point, the embryo begins to take on a much more elongated and recognizable shape, outlining what will eventually become the baby’s body. The processes of organ and tissue formation begin.
Eighth week: Fetal state
From the eighth week of pregnancy, the baby already has all its organs in the formation phase, although they are not yet fully developed. From this stage on, the embryo begins to be known as fetusAt this point, the arms, legs and fingers begin to clearly form, although development will continue until birth.
Organ formation
During this period, organogenesis occurs, that is, the formation of all the body systems, including the brain, the heart, lungs and other vital systems. Although the fetus already has all its organs at this stage, these will continue to mature over the following weeks until birth.
What is the difference between an embryo and a fetus?
Often, many people wonder what the difference is between embryo and fetus. This differentiation is crucial in terms of the biological development and it has to do with both the duration and the level of development achieved.
Key differences between embryo and fetus
- The term embryo It is used from the moment of fertilization until the eighth week of pregnancy. During this stage, the developing organism goes through different phases that include the morula and the blastocyst.
- The term fetus It is used from the eighth week, when the future baby already has all the organs in a primary state of formation, although they must continue to develop until the moment of birth.
- The main difference lies in the level of cellular specializationIn the embryo, cells divide rapidly and differentiate into the tissues and organs that will make up the body. In the fetus, these organs are already present and begin to function progressively.
Fetal development: week by week
Fetal development is a complex and incredible process. Here’s an overview of what happens during the different weeks of pregnancy:
Weeks 10-13
During these weeks, the fetus begins to experience rapid growth. Its kidneys They are already functioning, producing small amounts of urine. In addition, the fetus begins to move its limbs and has greater control over its muscles.
Weeks 14-17
At this stage, the genitals The fetus’s bones are already formed. Hair also begins to appear on its body, and the movements of its hands and feet are more coordinated. The skeletal system continues to strengthen.
Weeks 18-21
Around this period, the Eyebrows and scalp hair become more visible, and the hairs can begin to be detected. fetal movements In some pregnant women, reproductive organs such as the uterus are forming inside the fetus’s body.
Weeks 22-26
The development of the fetus progresses rapidly, gaining weight and increasing the amounts of body fat. Nails They also begin to become visible. This is a critical stage, as premature fetuses may have a chance of survival if they receive intensive care. From fertilization to birth, human development is a fascinating and complex process. The transformation of the zygote into an embryo, and then into a fetus, involves a series of crucial stages that allow for the formation of a fully developed human being. Understanding the differences between embryo and fetus It helps us appreciate the high level of organization that occurs during pregnancy and highlights the importance of each phase in ensuring a successful pregnancy.