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What is a Blastocyst?

During early development, a hollow cell mass composed of a trophectoderm, an inner cell mass, and a fluid-filled chamber or blastocoel is known as the blastocyst.


It forms between 5-14 days after fertilization in a process called blastulation.

The outermost layer forms the placenta and other supporting tissues necessary for embryonic development. Intestinal cells give birth to organs.

Embryonic stem cells isolated from intestinal cells are used for organ transplantation and regenerative medicine after trauma.

Blastocyst Formation

  • After fertilization, a single cell structure called a zygote is formed. The zygote undergoes a series of cell divisions to form a hollow mass of cells called the blastocyst.
  • The zygotes are enclosed in a zona pellucida that differs in that the whole process continues through the 2-cell, 4-cell, 8-cell, and 16-cell stages, and in the cleavage phase, the cells are known as blastomeres. In the 2-cell stage, blastomeres undergo mitosis and cytokinesis simultaneously.
  • After the development of an 8-cell or 16-cell embryo, the blastomeres form tight junctions with each other. This leads to spherical deformation and the formation of sugarcane-shaped groups of cells called morulae.
  • The interaction of blastomeres forms the outer cytoplasm and inner cytoplasm of embryos.
  • Fluid begins to accumulate within the zygote leading to the formation of the blastocyst. As fluid begins to accumulate, the blastocyst enlarges to form the blastocyst.
  • The blastocyst thus formed consists of two separate sections, the outer trophoblast and the inner cells.
  • Finally, the stretched zona pellucida ruptures to release the blastocyst. This is known as delivery. The blastocyst is then placed in the uterus.
  • The blastocyst attaches to the uterine wall of the uterus. This process of attaching the blastocyst to the uterine wall is known as implantation.


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