Module 4
1. Module 4
1.4. Page 2
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.