Of the various treatment options available for the treatment of infertility, none of the treatment procedures have had an impact on the society as much as in vitro fertilization. The use of these reproductive techniques has generated tremendous interest, concern and controversy in the recent years.
Human beings practice sexual reproduction, which involves the fusion of the sperm and ovum.
Sperm is the male gamete and a male probably makes and releases several trillion sperms during his lifetime. Sperm production does not begin until puberty. However it continues till the rest of life although the quality may be compromised with increasing age. The sperm is very small compared to the human egg and is made up of three major parts, the head, neck and the tail. The total length of the sperm is about 0.06 mm in human beings. The human sperm takes only about 3 months to mature and can be released instantaneously. So the sperm, which is ejaculated today, was manufactured 3 months ago!
The egg on the other hand, is already present within the female, although immature soon after birth. At the time of puberty, one of the eggs mature to be released by a process called as ‘ovulation’. The egg is roughly 5 times the size of an average sized cell in the human body. Ovulated at the rate of one egg per month for the next 35 to 40 years between puberty and menopause, these eggs will not be completely mature unless and until fertilized with a sperm.
One ejaculate from a fertile male contains at least 250 million sperm that is released into the female reproductive tract. These million sperms are swept to the fertilization site mainly by rhythmic contractions of the female reproductive tract and by swimming process. Out of the sperms attempting to fertilize the oocyte, only one sperm wins the battle against a million others. Certain chemical and electrical process initiated in the egg ensures that other sperms don’t fertilize with the oocyte. This is a remarkable mechanism conferred by Mother Nature to keep the population under control.
Fertilization is a sequence of events that begins with contact between a spermatozoon and an oocyte, leading to their fusion, which leads to the formation of a zygote and ends with the initiation of its cleavage.
With the union of egg and the sperm, another life begins. This new cell, now called as the zygote, immediately divides into two, then into 4, 8, 16 and so on. This happens a number of times giving rise to tissues, organs and organ systems and ultimately gives rise to a marvelously complex newborn of more than a trillion cells in just 38 weeks.