The Process of Conception Tests have proved that the first spermatozoa arrive at the upper ends of the uterine horns, and the entrance to the oviduct, only 25 seconds after the ejaculation. The interaction of sperm motility, contractions, and the flushing effect of the third ejaculation has already been discussed. The sperm and the ovum meet in the fallopian tube, the oviduct. The sperm penetrates the ovum the head of only one spermatozoon drives into the ovum membrane. The tail of the sperm, which serves only to propel the spermatozoa onward, is discarded at this point. The ovum and the spermatozoon unite to form a zygote in which the genes of both the parents are united. The Zygote divides to form a blastocyst. By means of cell division (mitosis), the embryo grows continuously. Within a period of approximately one week, the tiny embryo gravitates through the oviduct down into the uterus. On arrival there, it has attained the size of a minute mulberry, and is therefore, known as a morula. In order to clarify this stage of development, although the morula is the result of numerous cell divisions, this compact agglomerate of cells is only very slightly larger than was the original minute unfertilized ovum. That is to say, it has a diameter of one hundred and eighty thousandth of a millimeter! The layman cannot help but be filled with amazement to discover just how far scientists have been able to go in studying all these individual developments! On arriving in the uterus, the morula is now termed the blastula. The blastula implants itself in the mucous membranes of the uterus, a process that is known as the nidation. Nidation is completed approximately eighteen days after fertilization, and it is at this stage that the actual pregnancy commences.
Colour Key:
.JPG)
