Question

How is the embryo formed?

Answer 1

This is unhatched offspring in the process of development of a multicellular organism. Its development begins just after fertilization and continues through the formation of body structures, such as tissues and organs.

Complete answer:
Every month an egg is released from an ovary into the fallopian tube. The fallopian tube is the site for fertilization and it is facilitated by the cell lining of the tube.
- After sexual intercourse, sperm move from the vagina through the cervix and uterus to the fallopian tubes, where one sperm penetrates the egg and results in fertilization of the egg.
- The fertilized egg or zygote is propelled by the tiny hairlike cilia lining of the fallopian tube toward the uterus.
- The fertilized egg or zygote divides repeatedly as it moves down the fallopian tube to the uterus. It takes 3 to 5 days for a zygote to enter the uterus.
- In the uterus, the cells continue to divide and, forming a hollow ball of cells called a blastocyst.
- The blastocyst implants in the wall of the uterus about 6 days after fertilization, where it develops into an embryo attached to a placenta and surrounded by fluid-filled membranes. The process is called implantation and is completed in 9 - 10 days.
- The embryo develops from the inner cells in the thickened area of the zygote, and the outer cells burrow into the wall of the uterus and develop into the placenta. Several hormones are produced by the placenta that helps to maintain the pregnancy.
- If fertilization of that egg does not occur then it moves down into the uterus from the fallopian tube. In the uterus, it gets degenerated and moves out with the next menstrual period.

Note:
- The placenta is also responsible to carry the oxygen and nutrients from mother to fetus and waste materials from fetus to mother.
- In the embryo, almost all organs are completely formed by about 10 weeks after fertilization that is equal to 12 weeks of pregnancy.
- Most malformations or birth defects occur during the period when organs are forming in the embryo. So during this period, the embryo is said to be the most vulnerable to the effects of drugs, radiation, and viruses.