Main Difference – Blastula vs Gastrula
Blastula and gastrula are two stages of embryonic development of animals. Blastula develops from the rapid mitotic cleavage of cells in the zygote in a process called blastulation. Gastrula develops from the blastula by the movement of cell masses from the outside surface in a process called gastrulation.The main difference between blastula and gastrula is that blastula is an early development of an embryo, consisting of a spherical cell layer and a fluid-filled cavity whereas gastrula is a stage of the mature embryo with two or three cell layers.
Key Areas Covered
1. What is Blastula
– Definition, Structure, Formation
2. What is Gastrula
– Definition, Structure, Formation
3. What are the similarities between Blastula and Gastrula
– Common Features
4. What is the difference between Blastula and Gastrula
– Comparison of Key Differences
Key Terms: Archenteron, Blastula, Blastulation, Blastomeres, Blastocyst, Blastoderm, Blastocoel, Blastopore, Cleavage, Embryonic Development, Gastrula, Gastrulation, Invagination, Organogenesis, Morula, Trophoblast
What is Blastula
Blastula is a hollow ball of cells of in the early stages of development in an animal embryo. The egg cell of animals fertilizes from a sperm cell at the Fallopian tubes of the mother. After fertilization, the zygote undergoes a series of rapid cell divisions by mitosis while reaching the uterus. Following this, the process known as cleavage produces a ball of cells called morula. The cells in the morula are known as blastomeres. Once morula produces about hundreds of cells, it develops into blastula. Blastula consists of a spherical cell layer known as the blastoderm. The blastoderm surrounds the fluid-filled cavity known as blastocoel.
The blastula in mammals develops into the blastocyst. Blastocyst contains an inner cell mass (ICM), which is distinct from the blastula. The spherical cell layer of the blastocyst is called the trophoblast. The ICM in the blastocyst is referred to as the embryoblast. The trophoblast develops into the placenta, nourishing the embryo. The embryoblast is differentiated into different types of cells in the organism’s body. Once the blastocyst arrives at the uterus, it is embedded in the endometrium in a process called implantation. During implantation, the blastocyst hatches the zona pellucida, which is a thick, transparent membrane surrounding the mammalian ovum. The implantation is completed within 11-12 days later the fertilization. Once completely implanted in the endometrium, the blastula is referred to as an embryo.
Figure 1: Early Embryonic Development of Human
What is Gastrula
Gastrula is a stage of early embryo with two or three germ layers from which various organs are derived. Gastrula develops from the blastula in a process called gastrulation. The embryo undergoes massive rearrangements in its blastomeres, forming a multi-layered organism. Most of the surface cells in the embryo move to a new interior location. The three primary germ layers, endoderm, ectoderm, and mesoderm, are formed and organized in proper locations in the embryo during gastrulation in triploblastic organisms. The inward movement of the surface cells is called invagination. The invaginated cells are juxtaposed to the opposite side, converting the embryo into a double-walled cup, which gives rise to the endoderm and mesoderm. The remaining exterior cup becomes the ectoderm. In contrast, diploblastic organisms only contain two primary germ layers: endoderm and ectoderm. The blastocoel is eliminated by the invagination of cells. However, a new cavity develops in the hollow of the cup known as archenteron, which forms the rudiment of the animal’s future gut. The opening of the archenteron is called blastopore. After gastrulation, cells in the embryo undergo rapid diversification into the rudimentary form of various organs in the embryo in a process called organogenesis. Gastrulation is shown in figure 2.
Figure 2: Gastrulation
Similarities Between Blastula and Gastrula
- Blastula and gastrula are two multicellular embryonic stages of animals.
- Blastula develops into gastrula.
Difference Between Blastula and Gastrula
Definition
Blastula: Blastula is an animal embryo at the early stage of development when it is a hollow ball of cells.
Gastrula: Gastrula is an embryo at the stage following the blastula, when it is a hollow cup-shaped structure having three layers of cells.
Formation
Blastula: Blastula is formed from the morula in the process called blastulation.
Gastrula: Gastrula is formed from the blastula in the process called gastrulation.
Elaboration
Blastula: Rapid mitotic cell divisions result in the blastula.
Gastrula: Slow mitotic cell divisions result in the gastrula.
Structure
Blastula: Blastula is a single-layered, hollow structure.
Gastrula: Gastrula is a three-layered, hollow structure.
Movement of Cells
Blastula: Cells in the morula do not show any movement during the formation of the blastula.
Gastrula: Cell masses are migrated from the surface of the blastula during the formation of the gastrula.
Number of Cells
Blastula: Blastula contains 128 cells.
Gastrula: Gastrula contains more cells than blastula.
Cell Differentiation
Blastula: Blastula comprises of undifferentiated cells.
Gastrula: Gastrula comprises of differentiated cells.
Zona Pellucida
Blastula: Blastula comprises of a zona pellucida.
Gastrula: Gastrula lacks a zona pellucida.
Conclusion
Blastula and gastrula are two multicellular embryonic stages of animals. The main difference between blastula and gastrula is in the structure and components of each of the embryonic stages. Blastula develops from the morula in a process called blastulation. It comprises of an inner cell mass, which develops into the embryoblast. The outer cell layer is the trophoblast, which gives rise to the placenta. Gastrula develops from the blastula in a process called gastrulation. Massive movements of cell masses in the blastula develop the three primary germ layers: endoderm, ectoderm, and mesoderm.
Reference:
1. “Blastocyst Formation – Boundless Open Textbook.” Boundless. N.p., 31 Oct. 2016. Web. Available here. 10 June 2017.
2. Bowen, R. “Cleavage and Blastocyst Formation.” N.p., n.d. Web. Available here. 10 June 2017.
3. “Gastrula.” Encyclopædia Britannica. Encyclopædia Britannica, inc., n.d. Web. Available here. 10 June 2017.
4.”Gastrula: Definition & Concept.” Study.com. N.p., n.d. Web. Available here. 10 June 2017.
5. “Gastrulation and the 3 Germ Layers (Ectoderm, Endoderm & Mesoderm).” Study.com. N.p., n.d. Web. Available here. 10 June 2017.
Image Courtesy:
1. “Anatomy and physiology of animals Development & implantation of the embryo” By Sunshine Connelly (CC BY 3.0) via Commons Wikimedia
2. “Blastula” By Abigail Pyne – Own work (Public Domain) via Commons Wikimedia
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