Transport of Gametes, Selection of Spermatozoa and Gamete Lifespans in the Female Tract

Abstract

The meeting of male and female gametes at the ampullary-isthmic junction of the Fallopian tube, the usual site of fertilization, has attracted much attention, not least from the point of view of the temporal relationships underlying this critical process and the numbers of viable spermatozoa in the vicinity of the egg(s) at the time of activation. In farm and laboratory animals in which there is a clear relationship between the onset of receptivity to the male (the period of oestrus) and the subsequent time of ovulation, transport of eggs and spermatozoa to the site of fertilization is thought to involve carefully regulated processes, for the eggs are usually penetrated by spermatozoa shortly after release from the ovary into the reproductive tract. In the biological situation, therefore, a mechanism seems to have evolved for avoiding post-ovulatory ageing of the egg — a condition known to have deleterious consequences. In some contrast, the timing of gamete entry into the Fallopian tubes of primates, including women, may be widely asynchronous due to the absence of any specific phase of oestrus. It is also worth noting that procedures of artificial insemination in farm animals may lead to asynchrony in the meeting of the gametes and thus to a lowered fertility when compared with the results of spontaneous mating.