Question

Track the journey of the ovum from the ovary, its fertilization, and further development until the implantation of the embryo.

Answer 1

Hint: The life starts from a single cell stage called the zygote, which will undergo further division to form the baby. The process includes ovulation, fertilization, zygote formation, blastomere formation, implantation in the uterus, and parturition.

Complete answer:
The mature female gamete development is called oogenesis. Oogenesis will begin during embryonic development when more than a million oogonia (mother cells) forms within each of these ovaries. Oogonia will not be formed after the childbirth. The oogonia will meiotically undergo division and get arrested at prophase-I temporarily. This stage is called a primary oocyte. Each primary oocyte will then be surrounded by granulosa cell layers and they are called primary follicles.
Some of the primary oocytes degenerate before puberty. At puberty, 60000 to 80000 primary follicles will only be present. The primary follicles will now get surrounded by more layers of granulosa cells and theca cells. It is called a secondary follicle. The secondary follicle gets converted to the tertiary follicle and eventually, it forms the Graafian follicle. The Graafian follicle will release the secondary oocyte from the ovary. This process is called ovulation. The rest of the Graafian follicles will transform into corpus luteum. The corpus luteum secretes progesterone which maintains the endometrium. This is necessary for fertilization and further events during pregnancy. In the process of copulation, the semen will teach the ampullary-isthmic junction of the fallopian tube. The ovum that gets released from the ovary, will be transported to the ampullary-isthmic junction. When both the ovum and sperm simultaneously reach the ampullary-isthmic region, then fertilization will occur. After fertilization, the zygote starts to undergo mitotic division and moves towards the uterus. During division, the single-celled zygote will form a blastomere i.e., 2,4,8,16 celled stage. The blastomere is arranged into an exterior trophoblast layer and an inner cell mass. The trophoblast attaches itself to the uterus endometrial layer and the inner cell mass gradually forms an embryo. Post attachment, the cells in the uterus will undergo rapid division and will cover the blastocyst. Now, the blastocyst will be attached to the uterus endometrial layer. This is known as implantation and it further leads to pregnancy.

Note: The delivery of a baby is called parturition. The fully developed fetus and the placenta sends a signal which will stimulate mild uterine contraction. This contraction will cause oxytocin hormone from the pituitary. Oxytocin will further cause forceful myometrium contraction which will lead to the birth of the baby.