Question

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

Answer 1

Implantation is a stage of pregnancy where the embryo adheres to the wall of uterus and fertilization is that process where there is fusion of sperms and ovum.

Complete answer:
Let’s start with the events of fertilization in an adult human female first followed by implantation-
Fertilization and Implantation:
Fertilization is a process where there is fusion of the sperm and the ovum.
During coitus, sperms from the semen are released into the vagina from where it passes through the cervix of the uterus and reaches the ampullary-isthmic junction of the fallopian tube.
There is also release of ovum into this junction for fertilization to occur and then there is fusion of ovum and sperms which is known as fertilization.
During this process, the sperm induces changes in the zona pellucida and there is blockage of the entry of other sperms which ensures that only one sperm fertilizes an ovum.
There are enzymatic secretions of the acrosome which further helps the sperm to enter the cytoplasm of the ovum which causes the completion of meiotic division of the secondary oocyte that results in the formation of a haploid ovum and a secondary polar body.
Then the haploid sperm nucleus fuses with the haploid nucleus of the ovum in order to form zygote which moves through the cleavage and due to mitosis, there is formation of two, four, eight and sixteen daughter cells called blastomeres.
Then the 8-16 celled morula continues to divide to form the blastocyst whose cells are arranged into an outer trophoblast and an inner cell mass.
After the arrangement, this trophoblast gets attached to the inner lining of the uterus i.e., endometrium and this process is called Implantation which leads to pregnancy and the inner cell mass gets differentiated in order to form embryos.

Note: When the sperms are released from the semen, it enters into the vagina and it enters the junction where there is release of ovum too due to which sperms get fused with ovum and that process is known as fertilization. During implantation, a developing embryo makes contact with the uterine wall and remains attached to it until the birth.