oviducts

An oviduct is a reproductive duct that transports eggs from the ovary to the next stage of development. In most mammals, oviducts are paired tubes that connect the ovaries to the uterus, guiding the released oocyte toward fertilization and implantation. In many egg-laying animals, the oviduct is a longer canal that adds protective layers to the egg as it travels toward the exterior.

Within mammals, each oviduct consists of several regions: the fimbriae near the ovary, a funnel-shaped infundibulum that captures the oocyte, a wider ampulla where fertilization most often occurs, and a narrower isthmus leading to the uterine segment. The lining contains ciliated and secretory cells. Cilia and muscular contractions move the oocyte or zygote along the tract, while secretions provide nourishment and a suitable milieu for fertilization and early embryo development. The oviduct also participates in sperm transport and interaction within the reproductive tract.

Birds and many reptiles have a single, elongated oviduct that runs from the ovary to the exterior through the cloaca. It passes through distinct regions that add egg components in order: the infundibulum captures the yolk and may facilitate fertilization; the magnum secretes albumen; the isthmus deposits shell membranes; and the shell gland (uterus) forms the hard calcified shell before the egg exits.

Among vertebrates, oviducts vary widely in length, structure, and degree of specialization. In oviparous species, the oviduct is tightly integrated with egg formation and shell deposition; in mammals, it functions primarily as a conduit for the oocyte and early embryo and as the site of fertilization.

Clinically, oviduct health matters: in humans, obstruction or damage can prevent fertilization and can lead to ectopic pregnancy; procedures that block the oviducts are used for contraception.