1. Module 4

1.4. Page 2

Lesson 1

Module 4—From Fertilization to Birth

 

Explore

 

To begin to understand the changes that occur to the embryo and its supporting structures, including hormonal changes, it is recommended that you first complete the reading below. According to your own learning style, you may choose to make notes, a graphic organizer, a timeline, or another record of your learning. When you have completed the readings, watch the videos to complete your understanding and to learn about some reproductive technologies.

 

Read

 

ectoderm: germ layer that forms hair, nervous system, and skin

 

mesoderm: germ layer that forms muscle, bone, and muscular organs

 

endoderm: germ layer that forms gut lining, pancreas, and liver

 

zygote: the one-celled product of egg and sperm fusion; also known as the fertilized egg

 

cleavage: cell division in which the zygote divides into smaller, identical cells, called blastomeres, without increasing the total size of the cell mass

 

blastocyst: embryonic stage that results when the morula hollows out; the outer layer is the trophoblast and becomes the chorion; the inner cell mass becomes the embryonic disc

 

human chorionic gonadotropin (HCG): hormone released from the chorion after implantation; directs corpus luteum to continue making estrogen/progesterone, thereby maintaining the endometrium and preventing menstruation

 

gastrulation: the folding and differentiation of the embryonic disc into three germ layers, forming the embryonic stage called the gastrula

 

primary germ layers: three layers formed during gastrulation—endoderm, mesoderm, and ectoderm

 

morphogenesis: the development of body organs and structures; begins with gastrulation

 

differentiation: the turning on and off of genes in a cell; results in specialized cell functions

 

neurulation: the process of forming the embryo's neural tube, which will develop into the brain and spinal cord

 

allantois: extra-embryonic membrane that forms the foundation for the umbilical cord, which connects the fetus with the placenta

 

amnion: extra-embryonic membrane that is a closed, fluid-filled sac surrounding the fetus; protects the fetus from impact and temperature change

 

chorion: outermost layer of the embryo; develops from the trophoblast layer of the blastocyst; will form the fetal blood pool of the placenta

 

yolk sac: extra-embryonic membrane that produces first blood cells

 

placenta: embedded in the endometrium; provides a location where nutrients, gases, and wastes can be exchanged between fetal and maternal blood pools

 

umbilical cord: tube of blood vessels that connects the fetus to the placenta; for exchange of nutrients, gases, and wastes

 

ectopic pregnancy: occurs when fertilization and implantation take place in the oviduct

To understand how two gamete cells, each containing half the chromosome number of each parent, can combine and transform into an organism composed of millions of cells within just the first two months of gestation, you need to better understand fertilization, implantation, and embryonic development.

 

Read pages 508 to 519, “Section 15.1: Fertilization and Embryonic Development”, in the textbook.

 

Summarize this information according to your preference and learning style. A graph similar to “Figure 15.5” on page 512 of your textbook is helpful in understanding the homeostasis of hormones during pregnancy. A table summarizing the organs and systems that develop from the ectoderm, mesoderm, and endoderm is also useful. Ensure that your work includes descriptions of the following concepts:

 

  • fertilization
  • zygote
  • cleavage
  • blastocyst
  • implantation
  • human chorionic gonadotropin
  • gastrulation
  • primary germ layers
  • morphogenesis
  • differentiation
  • neurulation
  • allantois
  • amnion
  • chorion
  • yolk sac
  • placenta
  • umbilical cord

Many complications can arise during prenatal development. One of the first problems that can occur is that implantation in the uterine lining does not successfully take place. Implantation can happen in the oviducts, in other areas of the uterus, or in the abdominal cavity. Such an event is called an ectopic pregnancy.

 

Watch and Listen

 

Now that you have been introduced to the concepts and terminology of embryonic development, watch the following videos to gain further understanding of this important prenatal period. As you watch the videos, you may want to add information to your work for your course folder.