Question

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

Answer 1

Fertilization: It is the penetration of a mature ovum by the spermatozoa and fusion of the respective male and female pronuclei. In this process, the semen containing thousands of sperm is inseminated into the vagina. After the penetration and with the help of reproductive parts sperms start to clear their route in the fallopian tube to meet the ovum. More distance it covers, sperm count reduces and very few sperms reach the egg. An egg is covered by a protective layer called zona pellucida. The sperm on reaching the egg dissolves the egg membrane at the point of contact with the help of acrosome (a lysosome) present at the anterior region of the head of the sperm. Then releases its content inside the egg and fuses with the egg nucleus. Fertilization is accomplished in this step.As soon as fertilization has taken place the other sperms are prevented from entering the egg due to modification taking place in the egg cell membrane. Both sperm and egg can show their vitality only to a limited period of time. A sperm is alive for 48-72 hours in a female reproductive system and an egg can be fertilized until 24 hours from its release.

Implantation: Once fertilization happens, the cell starts to divide and multiply within 24 hours in the fallopian tube. This detached multi-celled structure is called zygote. Later, after 3-4 days it travels to the uterus and now we call it as the Blastula. The blastula then undergoes various stages and gets attached to the endometrial layer of the uterus. This process of attachment is known as implantation.