Sperm fertility, viability and persistence in the female tract.
This discussion considers the distribution of spermatozoa after coitus, the fate of spermatozoa, and fertility and vaibility of spermatozoa in the female tract. In most mammals spermatozoa are known to become distributed very rapidly following coitus, some reaching the site of fertilization in the ampulla of the oviduct with 5 minutes. Of special interest is the course of events in the human, the cow, and the sheep. These 3 species are grouped together because of important similarities--in the occurrence of intravaginal sperm deposition and in the fact that the uterine cervix is filled with a dense mucous plug through which the spermatozoa must pass. The cervical mucus varies greatly in nature at different stages of the estrous or menstrual cycle and at about the time of ovulation it is in the most appropriate state for sperm passage. The properties of cervical musus depend upon the fact that its main component is an extremely long chain mucoprotein with a highly variable degree of cross lingage between chains. Viscosity is directly related to degree of cross lingage, and this in turn depends on the hormonal status. At the beginning of the follicular phase the mucus is sparse in quantity and of high viscosity, and it also contains numerous cells. As the follicular phase advances, the effect of estrogen is to reduce viscosity and cell content and increase fluidity and elasticity. In 6-7 days around the period of ovulation mucus is readily penetrated by spermatozoa. The cervical mucus is secreted by glands that line the walls of the cervical canal. As the secretion flows towards the vagina it exhibits a distinct molecular orientation or strand formation which tends to direct spermatozoa moving up the vagina towards the walls of the cervical canal. The indications are that once spermatozoa have undergone capacitation they have a relatively limited life span. In most species the bulk of spermatozoa deposited in the female tract is evacuated to the exterior within a few hours--partly through mucus flow and partly through urine flush--and this would apply especially in animals with intravaginal ejaculation. It is clearly possible for spermatozoa, despite various means of disposal, to persist in secluded places for long periods. The fertility and viability of spermatozoa in the female ginital tract vary considerably in different species and in different parts of the genital tract in the same species. In the human, spermatozoa have been found in the cervix still motile at 8 days after intercourse.