Origin of new human life


Q.2. How Does the Origin of new human life takes place?

Ans. Single cell called zygote formed as a result of fertilization of ovum by sperm give rise to a human being. The zygote which starts as a single cell is invisible to the naked eye. The sperm and ovum are the two half cells and their fusion results in one cell which is the origin of the new human sex life. A sperm or spermatozoan is a specialized half cell that is actually half life in sense of that it can produce a new life by fusing with an ovum, though by itself it cannot create a new life.

A sperm has 23 unpaired chromosomes with 22 autosomes and 1 sex chromosome (X or Y). The Sex chromosome of the sperm determines the superior gender of the new life. Half of the sperms have X-chromosome with the potency to produce a female child while the other half have Y-chromosomes with the potency to produce a male child. It is indeed the sperm that determines the gender of a zygote. Of the nearly 300 million sperms that are shed in a single stages of intercourse only one is able to fertilize the ovum and that too is possible when the woman is in the ovulatory phase of menstrual cycle.

The ovum, like the sperm, has 23 unpaired chromosomes having 22 autosomes and 1 sex chromosomes (all X). As all the ova have X sex chromosomes, they have no role in determining the gender of the zygote. Like the sperm, the ovum also shares a half part in the formation of a new human sex  life. Graafian follicle is the matured primordial follicle. The Ovum is present in the graafian follicle in a projected area called cumulus oophorus. After the release of ovum from graffian follicle, the remaining part of graffian follicle forms the corpus luteum which produce female sex hormones.

Fertilization takes places only when the sperms enter the female genital tract. Muscular contractions of the uterus and fallopian tube create a suction for the sperms in the female tract. Each sperm is about 0.05 millimeter in length and consist of head, neck, body and tail. The head contains the nucleus having dense deoxyribose nucleic acid (D.N.A.) which is the genetic material. Fertiliasation of the ovum normally occurs in the lateral one-third of the fallopian tube that is the ampulla of the fallopian tube. The ovum retains the fertilizing capacity for 24-30 hours after ovulation. It takes less than one hour for the sperms to move from the place of discharge in the deep vagina to the place of fertilization in the lateral part of the fallopian tube covering a distance of 15-20 centimeters at the average speed of 3 millimeters per minute.
Some sperms even reach the ampulla, the place of fertilization within 10 minutes. The sperms move like a fish with the help of tail. The prostaglandins in the semen help in the locomotion of sperms both in the male and female genital tract. The sperms remain viable and active in the female genital tract for 48 hours. If the ovum is not available, all the sperms die and degenerate with 72 hours.

Fertilization is possible only if stages of intercourse is done two to three days before ovulation (as this is the time of survival of sperms) to one day after ovulation (as this is he time of survival of ovum). Both sperm count per milliliter of semen and the total quantity of semen should be high for dissolving the wall of ovum by hyaluronidase and making fertilization possible. Many sperms try to penetrate the ovum by only one sperm can enter it. the head and some part of neck of sperm enters the ovum to form male pronucleus while the body and tail degenerate. The pronuclei of the sperm and the ovum fuse to form the zygote. The zygote carries 22 + X plus 22 + X or Y number of chromosomes that is 44 + XX or XY that is 23 pairs of chromosomes. The one called zygote undergoes successive mitotic cleavages at a rapid speed. It takes about three days for the zygote to move through the fallopian tube to reach the uterus. It takes about 265 days or nearly 38 weeks for the zygote to develop in the uterus from the time of fertilization or about 280 days or 40 weeks from date of beginning to last menstruation after which it delivers out. The first three weeks of fertilization is called the germinal period. The zygote is called the embryo up to six weeks after fertilization and foetus beyond six weeks till the time of parturition. When the foetus has grown to the extent of being capable of survival outside the womb of the mother, it enters into the new world.