An embryo is the designation for a multi-cellular organism after it has successfully implanted in the lining of the uterus. Following implantation, the embryo's basic structures begin to differentiate and develop into areas that will form the head, chest, and abdomen.

Embryo

The placenta begins to form after the zygote attaches to the uterine wall, a key event of the early embryonic stage. This organ serves as a crucial interface between the pregnant person and the developing fetus, facilitating the transfer of nourishment and oxygen. It is also the pathway through which most substances ingested by the pregnant person, such as food, liquids, and medications, reach the fetus.

Placenta Formation and Function

Implantation is the process where the zygote, after dividing for approximately 7 to 10 days into a 150-cell organism, travels down the fallopian tubes and attaches itself to the uterine lining. This event marks the end of the germinal stage and the beginning of the embryonic stage.

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The germinal stage, lasting from conception through the first two weeks of prenatal development, is characterized by conception and rapid cell division through mitosis. During this fragile period, the mass of cells has not yet attached to the uterine lining, and fewer than half of all zygotes survive this initial stage.

Germinal Stage

Spielman, R. M., Jenkins, W. J., & Lovett, M. D. (2020, April 22). Psychology (2nd ed.). OpenStax. https://openstax.org/books/psychology-2e/pages/1-introduction

OpenStax Psychology (2nd ed.) Textbook

Conception is the moment when a sperm fertilizes an egg, resulting in the formation of a single-cell structure called a zygote. This event marks the beginning of a new organism and is when the parents' DNA is passed on to the child.

Conception in the Germinal Stage

Mitosis is the process of cell division that begins after conception, where the single-celled zygote divides exponentially. This fragile process involves the cell count growing from one to two, four, eight, and so on. Due to the delicate nature of this stage, fewer than half of all zygotes survive the first two weeks. As mitosis continues, the dividing cells become increasingly specialized, laying the groundwork for the formation of different organs and body parts.

Mitosis in the Germinal Stage

Implantation

A couple is trying to conceive. One week after ovulation, they get a positive result on a very sensitive home pregnancy test. However, about a week later, the woman begins her menstrual cycle as usual, and a follow-up test is negative. A doctor explains this was a very early pregnancy loss, which is a common occurrence.

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