Question:

Termination of gastrulation is indicated by

Updated On: Jul 9, 2024
  • obliteration of blastocoel
  • obliteration of archenteron
  • closure of blastopore
  • closure of neural tube.
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Solution and Explanation

Gastrulation is the process through which the presumptive areas of organ specific rudiments present on the surface of blastula move to their specific positions where these occur in the adult'. Gastrulation results in setting apart of the three primary germinal layers i.e., the ectoderm, mesoderm and endoderm from single layer of cells, the blastoderm, and in the formation of primordial gut or archenteron. Example in Amphioxus, blastula is ball- like with a large blastocoel surrounded by a single layer of columnar cells. At the onset of gastrulation, the blastoderm at the vegetal pole becomes flat. It gradually bends inwards till the embryo assumes the appearance of a double-walled cup. The cavity formed by invagination is called archenteron or primitive gut. Its opening is called blastopore and the embryo at this stage is gastrula. As a result of invagination, the presumptive endoderm, mesoderm and notochord are shifted from the surface to the interior of the embryo. The blastocoel is gradually obliterated till the two layers come in contact. By the completion ofgastrulation, the lateral horns of mesodermal crescent converge and come to lie on either side of the presumptive notochord.
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Embryonic Development

A successful pregnancy goes through several distinct stages. A man’s sperm must reach, penetrate, and fertilize a woman’s egg.

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3. Blastocyst Implantation

When the blastocyst outreach the uterus it implants in the endometrium, the mucus membrane which lines the uterus. The external cells of the blastocyst and the uterine inner lining, altogether, create the future placenta. A structure that transfers nutrients to the baby and removes his/her wastes is called the placenta.

4. Embryo Development

As the blastocyst reaches the final stage in the implantation process into the inner lining of the uterus, it evolves into a structure called an embryo. At this time, internal organs and external structures develop. The mouth, lower jaw, and throat are emerging, while the blood circulation system starts its evolution and a heart tube is created. The ears arise and arms, fingers, legs, toes, and eyes are being shaped. The spinal cord and the brain are already formed, while the digestive tract and sensory organs start their development. The cartilage is being replaced by the first bones.

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The embryo moves into the final stage of development by the twelfth week of fertilization, called the fetal stage. Till now, the fetus has formed all of the organs and structures that are necessary for a baby, but those organs still need to grow and develop.