Difference Between Blastocyst and Embryo

Key Difference – Blastocyst vs Embryo
 

The key difference between the blastocyst and the embryo is in the developmental stage in which they are formed. The blastocyst is formed at the blastula stage, whereas the embryo is formed when the blastocyst is implanted in the uterine wall.

Embryonic development in organisms takes place via different stages from the initial development of the zygote to the fetal stage. The blastocyst is the blastula stage in mammals that is developed after the morula stage. The embryo is referred to as the stage in which the blastocyst is implanted in the uterine wall.

CONTENTS

1. Overview and Key Difference
2. What is Blastocyst
3. What is Embryo
4. Similarities Between Blastocyst and Embryo
5. Side by Side Comparison – Blastocyst vs Embryo in Tabular Form
6. Summary

What is Blastocyst?

A blastocyst is simply referred to as the blastula stage in mammals. During the embryonic development of mammals, the zygote forms as a result of fertilization, and it undergoes a rapid cell division. Following these rapid divisions, the zygote is cleaved forming the morula. The morula stage then undergoes certain physiological and structural changes to develop into the blastula.

The cells of the morula are termed as blastomeres. When these blastomeres get surrounded by a fluid-filled cavity, it is known as the blastocoel. This stage is thus, referred to as the blastula stage. In mammals, the blastula stage is known as the blastocyst.The above process of developing the blastula from the morula is known as blastulation. During the embryonic development, the blastocyst formation in mammals begins after five days of fertilization.

The blastocyst is a thin-walled structure and it comprises of two main parts; the inner cell mass and the trophoblast. The inner cell mass eventually develops into the mature embryo. The trophoblast eventually develops into the extraembryonic tissue that includes the placenta. The structure of the blastocyst can be described by its diameter and the number of cells it contains. The diameter of the blastocyst is about 0.1-0.2 mm, and it is composed of about 200 – 300 cells.

There are important applications of the blastocyst during In vitro Fertilization (IVF). The blastocyst is used for IVF, and the blastocyst developed under in vitro conditions is implanted in the uterus. The inner cell mass of the blastocyst is also used to isolate embryonic stem cells that widely are used in animal cell culture research and experiments.

What is Embryo?

The Embryo is the developmental stage followed by the development of the blastocyst. The embryo is formed upon implantation of the blastocyst in the uterus. The period from second to the eleventh week after fertilization is referred to as the embryonic stage. During implantation, the inner cell mass of the blastocyst develops into the embryo.

The structure of the embryo contains two main embryonic disks known as the hypoblast and the epiblast. The function of the epiblast layer is to serve as the primitive endoderm and forms the amniotic cavity. The hypoblast functions in forming the exocoelomic cavity. The embryonic stage also characterizes certain evolutionary patterns in relation to the number of germ layers formed in the embryo.

The organisms that have only two germ layers; ectoderm, endoderm are known as diploblastic, whereas organisms have three germ layers; ectoderm, endoderm, and mesoderm are known as triploblastic. Formation of germ layers and the gut during the embryonic stage is known as gastrulation. Gastrulation is then followed by neurulation where the neural tissue is developed. Neurulation is then followed by organogenesis.

The embryo is also observed in flowering plants, where the seed is referred to as the embryo during plant development. The embryo is also used in extracting embryonic cells that are used to develop embryonic cell lines for research and for experimentation.

What are the Similarities Between Blastocyst and Embryo?

• Both Blastocyst and Embryo represent two stages in the embryonic development of an organism.
• Both Blastocyst and Embryo are formed as a result of fertilization between an egg cell and a sperm cell.
• Both Blastocyst and Embryo are diploid structures having 2n chromosomes.
• Both Blastocyst and Embryo are developed inside the female organism.
• Both Blastocyst and Embryo are used in diagnostics and animal cell culture.

What is the Difference Between Blastocyst and Embryo?

Summary – Blastocyst vs Embryo

The blastocyst and the embryo represent two important stages of the embryonic development in a mammal. The blastocyst represents the blastula stage in mammals. The blastula development takes place following the morula stage. The embryo is termed so forth upon the completion of the implantation process. Both blastocyst and the embryo are used in different in vitro applications. This is the difference between blastocyst and embryo.

Reference:

1.Britannica, The Editors of Encyclopaedia. “Blastocyst.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 14 Dec. 2014. Available here  
2.Findlay, et al. “Human Embryo: a Biological Definition | Human Reproduction | Oxford Academic.” OUP Academic, Oxford University Press, 18 Dec. 2006. Available here 

Image Courtesy:

1.’Blastocyst English’By Seans Potato Business (CC BY-SA 3.0) via Commons Wikimedia  
2.’Human embryo’By Anatomist90 – Own work, (CC BY-SA 3.0) via Commons Wikimedia