Topography and Anatomical Segments
The oviduct has a specific spatial orientation. Its proximal end pierces the uterine wall and opens directly into the uterine cavity. The distal end faces the ovary: anatomically it is not fused with it (free), but functionally in close contact.
Outside of ovulation, the distal opening is closed due to high smooth muscle tone. If this opening becomes pathologically patent, an abnormal communication forms between the oviduct lumen and the peritoneal cavity.
Morphologically, the tube is divided into four segments (from the ovary toward the uterus):
- Infundibulum (Infundibulum) — the distal end, equipped with fimbriae along its edges for efficient oocyte capture.
- Ampulla (Ampulla) — the longest segment of the organ, occupying about half of its length.
- Isthmus (Isthmus) — a narrowed segment located closer to the body of the uterus.
- Uterine part (Pars uterina) — the intramural segment running within the lateral wall of the uterus.
Histological Structure of the Wall
A complex-shaped lumen is clearly visible on a cross-section of the organ due to the structure of its inner layers. The oviduct wall is formed by three classic tunics:
1. Mucosa (Tunica mucosa) Forms massive, highly branched longitudinal folds that occupy most of the lumen. Lined by simple ciliated columnar epithelium, which contains two cell types:
- Ciliated cells: bear cilia on their apical pole, whose beating drives fluid flow and directs the movement of the ovum.
- Secretory (peg) cells: produce a mucous secretion necessary for the nutrition and protection of gametes and the zygote.
Beneath the epithelial layer lies the lamina propria (Lamina propria), formed by loose connective tissue.
2. Muscular layer (Tunica muscularis) Forms the main thickness of the wall. Composed of smooth muscle tissue with bundles separated by thin connective tissue septa. Consists of two layers:
- Internal: circular-spiral.
- External: longitudinal.
3. Serosa (Tunica serosa) The oviduct is almost entirely covered by peritoneum (intraperitoneally), forming the mesosalpinx. Histologically, this layer is represented by mesothelium with underlying connective tissue.
Physiology and Transport Mechanisms
Uterine tube activity is tightly synchronized with the phases of the female reproductive cycle:
- Capture Mechanism. During ovulation, the blood vessels of the infundibulum become actively engorged with blood. As a result, the tissue swells, and the fimbriae tightly embrace the ovary. Simultaneously, the tone of the infundibular myocytes drops, leading to the temporary opening of the distal ostium — the tube transforms into a receiver for the secondary oocyte.
- Transport Function. The oviduct provides slow, passive propulsion of the oocyte and developing embryo along with tubular fluid toward the uterine cavity. This process is driven by two factors: rhythmic beating of epithelial cilia and peristaltic contractions of the muscular layer.
Clinical Significance: Ectopic Pregnancy
Normally, embryonic transport to the uterus takes 4–5 days. If transport function is impaired, the developing embryo fails to relocate in time and implants directly into the tubal wall.
All layers of the tube are abundantly vascularized. This rich blood supply allows the embryo to successfully attach and begin development due to adequate trophic conditions. However, anatomically the oviduct wall is entirely unsuited for full fetal development, so this pathological (tubal) pregnancy typically ends in termination.