The fallopian tubes, also known as oviducts or uterine tubes, are muscular ducts connecting the ovaries and the uterus within the female pelvic cavity. They are far more complex than simple conduits, acting as the precise biological environment where human conception usually takes place. These dynamic organs capture the egg after ovulation, facilitate the journey of sperm, and nourish the fertilized egg before it travels to the uterus for implantation.
Physical Structure and Segments
The fallopian tube measures approximately 10 to 13 centimeters, organized into four distinct anatomical regions progressing from the ovary toward the uterus. The outermost section is the infundibulum, a funnel-shaped opening near the ovary. This segment includes finger-like projections called fimbriae, which sweep over the ovary surface to capture the ovulated egg.
Moving inward, the tube widens into the ampulla, the longest and most expansive part, making up about half of its total length. The ampulla narrows abruptly into the isthmus, a thick-walled section connecting to the final segment. The shortest segment is the intramural or interstitial part, which passes through the muscular wall of the uterus into the uterine cavity.
The wall consists of three layers: an outer serosa, a middle muscular layer (myosalpinx), and an internal mucosal lining. The muscular layer supports rhythmic contractions via smooth muscle fibers organized into inner circular and outer longitudinal layers. The innermost mucosa is highly folded, especially in the ampulla, and is lined by a specialized epithelium containing two main cell types.
Function in Ovum Transport and Fertilization
The primary role of the fallopian tube is to ensure the successful transport of the ovum and sperm, facilitating fertilization. Upon ovulation, the fimbriae become engorged with blood and sweep over the ovary, generating currents that guide the released egg into the infundibulum. This collection is necessary because the ovum is released into the peritoneal cavity.
Once inside, the ovum’s journey toward the uterus involves both cellular movement and muscular action. The mucosal lining contains ciliated epithelial cells that beat rhythmically toward the uterus, creating a flow that propels the ovum. This ciliary action is assisted by peristaltic waves, which are slow, rhythmic contractions of the muscular layer.
Fertilization most frequently occurs within the ampulla, where the egg and sperm meet. The zygote remains in the tube for approximately three to four days, undergoing its first stages of cell division while being transported toward the uterus. Secretions produced by the mucosal lining also nourish the sperm and the early embryo during this initial period.
When Things Go Wrong: Blockages and Ectopic Pregnancy
Disruptions to the structure and function of the fallopian tubes are a common cause of reproductive health issues. Tubal blockages occur when scar tissue forms within the lumen, preventing the passage of the ovum or sperm. This scarring is often a consequence of inflammation, most commonly caused by Pelvic Inflammatory Disease (PID) resulting from untreated sexually transmitted infections.
A partial blockage or damage to the ciliated cells can slow the transport of the fertilized egg, creating a risk for ectopic pregnancy. An ectopic pregnancy is the implantation of a fertilized egg outside of the main cavity of the uterus; about 90% of these cases occur within the fallopian tube itself. Since the tube is not designed to support a growing embryo, development can cause the tube to rupture.
Tubal rupture is a medical emergency that can lead to severe internal bleeding and life-threatening complications. Conditions such as endometriosis, prior abdominal surgery, or a history of a previous ectopic pregnancy increase the likelihood of transport failure and subsequent tubal issues.