Physiology of gamete and embryo transport through the fallopian tube.

A great deal is now known about the migration of spermatozoa within the female reproductive tract, and how they interact with the oocyte and achieve fertilization in a variety of species. The process involves a series of complex features. It is a mixture of active and passive transport and active migration, with drastic jumps in the numbers of spermatozoa that migrate beyond specific physiological checkpoints, and with interactions occurring between spermatozoa, epithelium and luminal fluid. A reservoir of spermatozoa forms, at a discrete location, to hold and liberate spermatozoa in a gradual fashion. After fertilization has occurred, zygotes are passively transported to the uterus by a series of closely coordinated mechanical events where activities of cilia and smooth muscle predominate. Passage of the embryo from oviduct to uterus is regulated and timed by ovarian hormones, signals associated with mating, and zygotic substances. The diverse and exquisite patterns and regulatory signals typical of sperm migration and ovum transport across many species provide fascinating examples of adaptations according with differing reproductive strategies in various mammals.