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Blastocyst is referred to as the embryo containing one hundred to one hundred and fifty cells. At this stage after fertilization (approximately five days) the embryo will move from the fallopian tube to the uterus.
| Table of Contents |
Keyterms: Blastocyst, Embryo, Fallopian tube, Uterus, Trophectoderm, Cells, Embryonic stem cells, Tissue, Cell division
Also Read: Class 12 Fertilization
Blastocyst Definition
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The hollow mass of cells that are formed during trophectoderm, the early development of cells with the inner cell mass, and fluid-filled cavity or blastocoel are known as the blastocyst.
A blastocyst is formed by the blastulation process between 5-14 days after fertilization. The placenta and other supportive tissues form the outermost layer for the development of the fetus. The inner cell mass from the body tissues. The embryonic stem cells become separated from the inner cell mass and form the tissue replacement which is damaged by injury and regenerative medicine. Only mammals can form a blastocyst.
Blastocyst Formation
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After fertilization, the zygote is formed which is a single-celled structure called the. The zygote undergoes different kinds of cell division by which a hollow cell mass is formed which is known as the blastocyst.
The stages of the formation of the blastocyst are:
- The zygote is enclosed in the zona pellucida and divides into a process of 2-celled, 4-celled, 8-celled, and 16-celled stages. The cells during the cleavage stage are blastomeres stages. The blastomeres during the 2-celled stage divide in the mitosis and cytokinesis process simultaneously.
- After forming an 8-celled or 16-celled embryo, the blastomeres build tight junctions with one another which can deform the round shape and form a mulberry-shaped cluster of cells known as a morula.
- The junction between the blastomeres builds outer cell mass and an inner cell mass for the embryo.
- The fluid then accumulates inside the zygote for the formation of the blastocyst. The fluid starts accumulating, and the blastocyst starts expanding.
- The blastocyst is made by two distinctive tissues which are the outer trophoblast and the inner cell mass.
- The stretched zona pellucida breaks and releases the blastocyst after a time which is known as hatching. The blastocyst is then implanted in the uterus.
The blastocyst attaches to the endometrial wall of the uterus and this process of attachment of the blastocyst with the uterine wall is known as implantation.
Also Read:
| Related Articles | ||
|---|---|---|
| Double fertilization | Budding | Fragmentation |
| Pollination | Gemmule formation | Polyembryony |
Similarities and Dissimilarities between Blastocyst and Embryo
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Similarities:
- Embryo and blastocyst are both diploid structures.
- Both of them are formed by the fertilization of gametes.
- Both have potent cells and are used for diagnostic processes.
- Both are developed inside a mother’s body.
Dissimilarities:
| Blastocyst | Embryo |
|---|---|
| It is a hollow, thin-walled structure during the early stage of the development of the embryo. | It is the undeveloped stage of a living animal which has the capability of development. |
| The name of the process of formation is blastulation. | The process of Embryo development is gastrulation, neurulation, and organogenesis. |
| This is formed by the cleavage of the zygote. | The embryo is developed from the inner cell mass of the blastocyst. |
| Take 5-14 days for development after fertilization. | Takes 2-11 weeks after fertilization. |
| In the in-vitro process, a High pregnancy rate is observed. | In-vitro fertilization low pregnancy rate is observed. |
| Found in mammals. | Found in both plants and animals. |
Blastocyst Structure
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There are two types of Blastocyst:
- The inner cell mass, which is known as the embryoblast, from which primitive endoderm and the embryo proper (epiblast) is developed. The primitive endoderm forms an amniotic sac. The epiblast gives rise to the three germ layers such as endoderm, mesoderm, and ectoderm.
- The trophoblast forms the outer ring of the blastocyst which is also a secreted factor of the blastocoel. After implantation, cytotrophoblast from the inner layer of the trophoblast, made by stem cells such as chorionic villi, placenta, and syncytiotrophoblast. The syncytiotrophoblast is the outermost layer of the trophoblast secreting proteolytic enzymes breaking the endometrial extracellular matrix for implantation of the blastocyst in the uterine wall. The blastocoel fluid cavity has some amino acids, growth factors.
Read More: Male and female reproductive system
Cell Specification in Blastocyst
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Multiple processes have specifications in blastocyst for controlling cell lineages such as trophoblast, epiblast, and primitive endoderm. These processes involve gene expression, cell signaling, cell-cell contact, etc.
After ICM has been growing within the blastocyst, the cell mass prepares for the epiblast and primitive endoderm. This process of the specification is controlled by fibroblast growth factor (FGF) which is generated by the MAP kinase pathway for cellular genomes.
Things to Remember
- Blastocyst is a part of CBSE Class 12 term 1 Biology syllabus.
- It comes under unit 6, Reproduction chapter 3 Human Reproduction and carries 5 to 6 marks
- Blastocyst is referred to as a structure that forms in an early stage of pregnancy.
- Blastocyst contains inner cell mass (ICM) which gradually develops into embryos.
- Blastocyst formation takes five days after fertilization.
- Blastocyst culture is important in IVF in order to increase the success rate.
Read More About Parturition
Sample Questions
Ques. What is the number of cells present in blastocyst? (1 mark)
Ans: On Day 5, the embryo is called a blastocyst, which has about 70-100 cells. Among the blastocyst cells, two different types of cells are present. The first division is called the inner cell mass, from which fetal tissue is developed.
Ques. How is blastocyst affected? (1 mark)
Ans: There are no clinical factors that significantly affect the number of cells present in blastocysts as well as pregnancy rate, or implantation rate. But the numbers of oocytes, zygotes, and naturally developing embryos can significantly affect the blastocysts production in vitro.
Ques. Write the number of types of cells present in the blastocyst? (1 mark)
Ans: The blastocyst is made by two types of cells as the inner cell mass (ICM, from which the fetal tissues develop) and the trophectoderm (which will form mostly extraembryonic tissues such as the placenta
Ques. What is the function of the blastocyst? (1 mark)
Ans: The blastocyst possesses an inner cell mass which helps in the development of an embryo which finally develops into a baby, and the outer layer of cells, which is known as the trophoblast, forms the placenta which provides nourishment and protection to the embryo.
Ques. What is a good blastocyst grade? (1 mark)
Ans: Grade 1 through 2.5 embryos are considered good embryos for developing to the blastocyst stage.
Ques. What is the duration of the blastocyst stage? (1 mark)
Ans: The duration of the blastocyst stage is five to six days after fertilization.
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