Question

Explain the events that take place once a sperm reaches the oviduct till it becomes a foetus. Write the role of placenta in pregnancy.

Answer 1

Step 1: Fertilization in the oviduct
When a sperm reaches the oviduct (also called fallopian tube), it may meet an ovum (egg) released during ovulation.
- If a sperm successfully penetrates the egg, fertilization occurs.
- The nuclei of the sperm and egg fuse to form a zygote (a single-celled fertilized egg).

Step 2: Formation of embryo
- The zygote begins to divide repeatedly by mitosis as it moves towards the uterus.
- This series of divisions forms a ball of cells called the embryo.

Step 3: Implantation in the uterus
- The embryo reaches the uterus in about 4–5 days.
- It attaches itself to the thick and soft lining of the uterus, a process called implantation.

Step 4: Development into a foetus
- After implantation, the embryo continues to grow and develop organs.
- By the end of about 8 weeks, the embryo is called a foetus, which has a recognizable human form.

Role of placenta in pregnancy:
- The placenta is a special tissue that forms a connection between the developing foetus and the uterine wall of the mother.
- It allows the transfer of nutrients, oxygen, and antibodies from the mother’s blood to the foetus.
- It also helps remove waste products like carbon dioxide and urea from the foetal blood to the mother’s blood for disposal.
- Additionally, the placenta secretes hormones that help maintain pregnancy (like progesterone).

Conclusion:
Once the sperm reaches the oviduct and fertilizes the egg, a zygote forms, develops into an embryo, and implants in the uterus. It grows into a foetus, nourished and supported by the placenta throughout the pregnancy.