Fertilization is the amazing process of combining male and female gametes to form a diploid zygote, crucial for human reproduction.
This complex event usually happens in the ampulla of the fallopian or uterine tube, paving the way for the embryo’s development in the protective environment of the uterus.
Sperm Movement towards Egg:
The journey commences with the ejaculation of semen, a complex mixture of sperms and various secretions.
This coagulated semen undergoes liquefaction, activating sperms. Capacitation, spanning 5-6 hours, transforms the acrosome membrane, infusing sperms with increased activity.
Prostaglandins, female secretions, and uterine contractions collectively facilitate the remarkable ascent of sperms from the vagina to the ampulla.
Sperm Entry into Egg:
Out of the staggering 200 to 400 million sperms, a select few hundred navigate the intricate path to the ampulla, where only one sperm successfully fertilizes the ovum.
The acrosome reaction, a critical phase, unleashes lysins such as hyaluronidase and corona-penetrating enzymes, dissolving cells in the corona radiata.
Fertilizin interactions guide the sperm, initiating essential reactions, including depolarization and membrane dissolution.
Activation of Ovum:
Before fertilization, the ovum rests in metaphase II. Upon the pivotal contact with the sperm head, it undergoes activation, resuming and completing meiosis II.
This transformative process results in the formation of the second polar body and the organization of the germinal vesicle into the female pronucleus, often referred to as the true ovum or egg.
Fusion of Egg and Sperm:
As the zygote takes shape, the coverings of the male and female pronuclei undergo degeneration, facilitating chromosomal pairing in a process known as syngamy.
This intricate dance of genetic material results in the formation of a synkaryon, aided by the proximal centriole received from the sperm.
This, in turn, initiates the cleavage of the cell into two blastomeres, marking the inception of embryonic development.