31.19: Uterine Tubes

The uterine or fallopian tubes function as the conduit through which oocytes travel from the ovaries to the uterus. Each fallopian tube measures approximately 10 to 13 cm long and is anatomically divided into the infundibulum, ampulla, isthmus, and interstitial part (or intramural segment). The infundibulum is characterized by its funnel shape and features extensions called fimbriae which reach towards the peritoneal cavity. These fimbriae play a critical role during ovulation as they extend over the ovaries to capture the released oocyte.

The ampulla, which constitutes over half the length of the uterine tube, is the most common site of fertilization. It is the widest section of the tube and provides an optimal environment for the sperm to meet the oocyte. Once the oocyte is released from the ovary, it is captured by the fimbriae and guided into the ampulla. Here, if a sperm is present, fertilization occurs. The fertilized egg, initially called a zygote, then moves through the isthmus, the narrowest part of the tube, before reaching the uterus for implantation, which occurs a few days later.

The inner lining of the fallopian tubes is equipped with ciliated epithelial cells, which generate currents in the peritoneal fluid. This fluid, which is present in the peritoneal cavity, is crucial for transporting the oocyte towards the uterus. The cilia's movements create a current in the fluid, pushing the oocyte along the tube. Additionally, nonciliated secretory and peg cells within the epithelium produce a nourishing fluid that sustains the oocyte during its journey. Complementing the cilia's efforts are peristaltic contractions of the surrounding smooth muscle layers, which further assist in moving the oocyte along the ampulla towards the isthmus.

This sophisticated coordination of structures and functions ensures the oocyte's safe passage, optimal fertilization conditions, and subsequent transportation to the uterus.