<P> A cross section of Fallopian tube shows four distinct layers: serosa, subserosa, lamina propria and innermost mucosal layer . The serosa is derived from visceral peritoneum . Subserosa is composed of loose adventitious tissue, blood vessels, lymphatics, an outer longitudinal and inner circular smooth muscle coats . This layer is responsible for the peristaltic action of the Fallopian tubes . Lamina propria is a vascular connective tissue . There are two types of cells within the simple columnar epithelium of the Fallopian tube (oviduct). Ciliated cells predominate throughout the tube, but are most numerous in the infundibulum and ampulla . Estrogen increases the production of cilia on these cells . Interspersed between the ciliated cells are peg cells, which contain apical granules and produce the tubular fluid . This fluid contains nutrients for spermatozoa, oocytes, and zygotes . The secretions also promote capacitation of the sperm by removing glycoproteins and other molecules from the plasma membrane of the sperm . Progesterone increases the number of peg cells, while estrogen increases their height and secretory activity . Tubal fluid flows against the action of the ciliae, that is toward the fimbrial end . </P> <P> In view of longitudinal variation in histological features of tube, the isthmus has thick muscular coat and simple mucosal folds; whereas ampulla has complex mucosal folds . </P> <P> When an oocyte is developing in an ovary, it is encapsulated in a spherical collection of cells known as an ovarian follicle . Just prior to ovulation the primary oocyte completes meiosis I to form the first polar body and a secondary oocyte which is arrested in metaphase of meiosis II . This secondary oocyte is then ovulated . The follicle and the ovary's wall rupture, allowing the secondary oocyte to escape . The secondary oocyte is caught by the fimbriated end and travels to the ampulla of the uterine tube where typically the sperm are met and fertilization occurs; meiosis II is promptly completed . The fertilized ovum, now a zygote, travels towards the uterus aided by activity of tubal cilia and activity of the tubal muscle . The early embryo requires critical development in the Fallopian tube . After about five days the new embryo enters the uterine cavity and on about the sixth day implants on the wall of the uterus . </P> <P> The release of an oocyte does not alternate between the two ovaries and seems to be random . After removal of an ovary, the remaining one produces an egg every month . </P>

The segment of the uterine tube where fertilization occurs is
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