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Briefly Explain the Events of Fertilisation and Implantation in an Adult Human Female. - Biology

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Briefly explain the events of fertilisation and implantation in an adult human female.

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Solution

During coitus, the semen is released into the vagina, passing through the cervix of the uterus and reaching the ampullary-isthmic junction of the fallopian tube.

  • The ovum is also released into the junction for fertilisation to occur.
  • The process of fusion of the sperm and the ovum is known as fertilisation.
  • During fertilisation, the sperm induces changes in the zona pellucida and blocks the entry of other sperms. This ensures that only one sperm fertilises an ovum.
  • The enzymatic secretions of the acrosomes help the sperm enter the cytoplasm of the ovum.
  • This causes the completion of meiotic division of the secondary oocyte, resulting in the formation of a haploid ovum (ootid) and a secondary polar body.
  • Then, the haploid sperm nucleus fuses with the haploid nucleus of the ovum to form a diploid zygote.
  • Mitosis starts as the zygote moves through the isthmus of the oviduct (cleavage) and forms 2, 4, 8 and 16 daughter cells called blastomeres.
  • The 8−16 cell embryo is called a morula, which continues to divide to form the blastocyst. The morula moves further into the uterus.
  • The cells in the blastocyst are arranged into an outer trophoblast and an inner cell mass.
  • The trophoblast gets attached to the uterine endometrium and the process is called implantation. This leads to pregnancy.
  • The inner cell mass gets differentiated to form the embryo.
Concept: Fertilisation and Implantation
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