The Fallopian or uterine tubes are a pair of ducts which are attached to the upper and outer corners of the uterus. Each is approximately four inches long and about a quarter of an inch thick, although the size varies in its different parts. The ampulla or outer end of the Fallopian tube forms a runnel-like opening where the wall divides into finger-like processes called fimbriae. These not only guard the opening but, being close to the ovary, they also help to sweep the ovum into the canal of the tube itself. Fertilization occurs in the outer part of the Fallopian tube in the region of the fimbriae.
The Fallopian tubes consist of a fairly thick muscular coat surrounding a very complex inner lining, or mucous membrane, which secretes special material to nourish both the sperms and the fertilized ovum.
The function of the Fallopian tube is essentially twofold in nature. Firstly, it forms a route whereby the sperms migrate from the uterus to the ovary, and it possesses certain vital characteristics which enable it to nurture and look after sperms. It is commonly believed that sperms remain alive and capable of fertilization for two or even three days in the outer fimbriated part of the Fallopian tube and they are thus readily available when ovulation occurs. Secondly, the Fallopian tube is the home of the newly fertilized ovum for the first seven days of its life. If the ovum is not fertilized it can only survive for 12 or perhaps 18 hours. Fertilization occurs on the 14th day of a 28-day menstrual cycle at the time of ovulation. Immediately after fertilization the ovum enters the fimbriated end of the Fallopian tube (or fertilization actually occurs within the Fallopian tube) and it does not reach the cavity of the uterus until the 21st day. The Fallopian tube supplies the newly-fertilized ovum with all its nutrition and requirements during these seven days. On the seventh day after fertilization the ovum will have developed chorionic villi which are special protrusions on the outer side of the fertilized egg which enable the pregnancy to embed within whatever maternal tissue is nearest or most convenient at the time. It is, therefore, vital that the journey of the fertilized ovum along the Fallopian tube should take precisely seven days, no more and no less. If the ovum arrives in the cavity of the uterus before the seventh day it is unable to embed itself and therefore dies, or conversely if it fails to arrive in the cavity of the uterus by the seventh day it embeds itself within the Fallopian tube and forms an ectopic or tubal pregnancy.