Embryo and Placenta Development Overview

Development of Embryo and Placenta

The development of the embryo and placenta is a complex process that involves various interactions between the embryo, the maternal endometrium, and the placental tissue. Over the course of the 20th century, numerous researchers studied the process of implantation and the structure of the embryo and placenta. This article provides an overview of the development of the embryo and placenta, focusing on the process of blastocyst implantation and the role of the placental tissue in fetal development.

Blastocyst Implantation

Blastocyst implantation is the process by which the embryo attaches to the uterine endometrium, initiating the development of the placental tissue. The implantation process varies between species, with some, like humans and guinea pigs, having invasive blastocysts that break through the uterine lining and invade the uterine tissue. In contrast, other species, such as sheep and pigs, have less invasive blastocysts that do not invade the uterine stroma.

Historically, researchers have studied the structure of the embryo and placenta during implantation, with many focusing on the human embryo. Hertig et al. described the development of human embryos during the first 17 days of life, including the process of implantation, and collected human ova for study. These investigations provided valuable insights into the implantation process and the structure of the embryo and placenta.

Placental Development

The placental tissue plays a crucial role in fetal development, providing nutrients and oxygen to the fetus while removing waste products. The placental tissue undergoes significant changes throughout pregnancy, adapting to the maternal environment and maintaining appropriate placental function.

The placental barrier, composed of cells from the chorionic villi, prevents direct contact between maternal and fetal blood, allowing for the biosynthesis, metabolism, and transport of various molecules, including steroids, to occur within the placental tissue. The chorionic villi are composed of several cell types, including the syncytiotrophoblast (STB) and cytotrophoblast, which contribute to the placental barrier and support fetal development.

Epigenetic Regulation

Epigenetic regulation plays a significant role in fetal development and normal fetal development is dependent on proper development of the embryo and placenta. Epigenetic signals, such as DNA methylation, are involved in stable gene repression and are essential for maintaining appropriate gene expression patterns during fetal development.

Species-Specific Placental Anatomy

While there is no perfect animal model for the human placenta, higher order primates such as old world monkeys are most closely aligned to humans in terms of placental anatomy and function. Understanding the species-specific placental anatomy and endocrine function of relevant animal models is crucial for studying the function of the human placenta and for identifying potential developmental issues.

Open Research Questions

There are several open research questions in the field of embryo and placental development, including the role of oxygen in trophoblast invasion, the regulation of steroid biosynthesis, transport, and exchange by the placental tissue, and the impact of maternal hormones on placental development.

In conclusion, the development of the embryo and placenta is a complex process that involves a series of interactions between the embryo, the maternal endometrium, and the placental tissue. Understanding the implantation process and the role of the placental tissue in fetal development is crucial for maintaining optimal fetal growth and development and for identifying potential developmental issues.