Fertilization Process.

the process of fertilization from where it begins. Before ovulation, mucus is secreted which is extremely stretchable. This is the highly fertile period for chancing conception. As it is the mucus that carries the sperm into the uterus.


During intercourse the excitement dilates the arterioles that supplies the blood to the penis. The blood then is accumulated in three cylindrical soft sinuses that move through the penis lengthwise. They cause pressure that enables the penis to enlarge, get erect and penetrate the vagina.


Straddling increases the tension to end in ejaculation where the walls of the vas deferns contract and force the sperm out. On the way out seminal vesicles, Cowper's glands, and the prostate glands add some more fluids. These fluids are like a source of energy they provide a chemical environment for the sperm. Although males can release 200-300 million sperm, it only takes one to penetrate the egg.   When the sperm is mixed with these fluids it is called semen. It helps the mobility of the sperm into the urethra and to the vagina.


  


From the vagina the sperm moves on to the egg i.e. through the fallopian tubes to the egg (i.e. if the egg is present). The sperm swims for several centimetres every second but the muscular movement of the wall of the uterus and the tubes helps its mobility. Research also claims that the egg attracts the sperm through some chemical secretions.


However, the sperm takes at least 15 minutes to reach the egg. At any ejaculation a hundred thousand sperms are flushed out. Out of these only a few reach the urethra and only one breaks the egg.


When the sperm reaches the egg, fertilisation begins. First the head of the sperm gets attached to the egg. As they merge the concerned membranes take in all the contents of the sperm into the egg. Immediately the egg releases the cytosol from the egg that makes it impenetrable for the other sperms that arrive.


Then the nucleus of male increases in size to form the male pronucleus and the egg enlarges to form the female pronucleus. These two nuclei then move to form a set of chromosomes, this them is the fertilized egg or zygote.


The Zygot contains 46 chromosomes, 23 from each parent cell.  As the zygote travels to the uterus, it divides, forming a cluster of cells (the morula) by about 3 days after fertilization.


 The morula develops a cavity and is now known as a blastocyst, which will become the embryo.  This blastocyst floats freely within the uterine cavity for about 48 hours before attaching itself to a site in the endometrium (uterine lining).

        About 10 days following fertilization, the blastocyst is completely imbedded into  the endometrium, and forms the placenta.  Within the cell cover of the blastocyst's cavity, it then develops into a fluid- filled sac covering the embryo, and the yolk sac.