Fallopian (fuh-LOH-pee-un) tubes, also called oviducts, are 4-inch-long trumpetshaped tubes that extend laterally from the sides of the uterus. From the side of the uterus, the tube expands into an ampulla, or widening, which curves around to a trumpet-shaped end, the infundibulum (in-fun-DIB-bue-lum). At the end of the infundibulum there are fingerlike projections that curl around the ovary, poised to accept ova when they are released (see Figure 4.3).
Once a month an ovary releases an ovum that is swept into the Fallopian tube by the waving action of the fimbriae (FIM-bree-ee). The fimbriae sense the chemical messages released from the ovary that signal the release of the ovum and begin a series of
muscular contractions to help move the ovum down the tube. If the Fallopian tube is long and flexible, it may even be able to catch the released ovum from the opposite ovary; some women with a single active ovary on one side and a single functioning Fallopian tube on the other have been known to get pregnant (Nilsson, 1990).
The inner surface of the Fallopian tubes are covered by cilia (hairlike projections) whose constant beating action creates a current along which the ovum is conducted toward the uterus. The entire transit time from ovulation until arrival inside the uterus is normally about 3 days. Fertilization of the ovum usually takes place in the ampulla because, after the first 12 to 24 hours, postovulation fertilization is no longer possible. Occasionally, the fertilized ovum implants in the Fallopian tube instead of the uterus, causing a potentially dangerous ectopic pregnancy (see Chapter 12).