Essay by PaperNerd ContributorCollege, Undergraduate April 2001

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PREGNANCY Conception occurs after a fertile mating in which the spermatozoa deposited in the vagina reach an ovum shortly after ovulation. Before coitus penis becomes enlarge due to engorgement of its blood vessels brought about chiefly by the dilation of the arterioles but partly by the contraction of the muscle which obstructs the venous outflow from the organ. In the woman the clitoris also becomes erect and the vagina exudes mucus which facilitates the passage of the penis into the vagina. The cervix contributes very little to this lubricating effect. During orgasm in the female, which should occur simultaneously, it is likely that the os uteri dilates, because spermatozoa have found in the uterus a few minutes after coitus. Coitus is accompanied by psychic excitement and must be regarded primarily as a cerebral event. After ovulation cervical mucus changes to clear, thinner, alkaline, egg white like texture which sperms like that environment and cause of this is the increase estrogen level in the blood stream, it also stimulate growth of myometrium and prepares mammary glands for lactation.

Progesterone is responsible for suppressing uterine contraction and formation of mucus plug.

Pregnancy does not occur unless many millions of sperms are deposited in the vagina, although only one sperm is necessary for the fertilization of an ovum. 100% of sperms gets in the vagina but only 3% gets to cervical wall, 0.1 % to uterus, and 0.01% to ampulla, barely any sperm will get to the egg, once a single sperm enters the egg a chemical signal takes place to block polyspemy, the head of the sperm has an enzyme which is use to break into the surface of the egg, it has all the information of the parent gene and it also has the DNA to combine with the DNA of...