Question

Explain the process of fertilization, development and birth in human beings.

Answer 1

Hint: Humans are sexually reproducing and viviparous that involves the fusion of one human egg and sperm resulted in the production of the zygote.

Complete answer
Fertilization: Fertilization involves a process in which sperm fuses with ovum and it usually occurs in the fallopian tube. The fertilization resulted in a formation of Zygote and it takes about five days to reach the uterus from the uterine tube. In the zygote, the mitotic division starts through the isthmus of the oviduct called cleavage. After division, it forms 16 celled stages called blastomeres. The blastomeres in the blastocyst are arranged into an outer layer called trophoblast and an inner group of cells called the inner cell mass. The blastocyst gets embedded in the endometrium of the uterus called implantation that leads to pregnancy.

Development:
After implantation, finger-like projections seen on the trophoblast are called chorionic villi that combine with the uterine tissues to form the placenta. Placenta helps in the supply of oxygen and nutrients to the embryo. In this stage, the embryo differentiates into an outer layer called ectoderm and an inner layer called endoderm. A third layer appears between the two-layers called mesoderm. These three layers lead to the formation of tissues and finally organs. After the 9 months of pregnancy, the fetus is fully developed and is ready for delivery.

Birth:
The method of childbirth is called parturition that is initiated by a complex neuroendocrine mechanism. Oxytocin is a hormone which is responsible for the stronger uterine contractions. The stronger contraction leads to the expulsion of the baby out of the uterus through the birth canal. It happens by opening the cervix and the baby is released out through the vagina.

 Note:
- The placenta is considered as a structural and functional unit between the embryo and mother.
- The sex of the embryo is determined by the presence of the X or Y chromosome in the sperm.
- Viviparity is the development of the embryo inside the body of the parent that leads to living young individuals.