The fallopian tubes are important structures in the female reproductive tract, which connect the peritoneal cavity with the uterine cavity. They provide a site for fertilisation and are involved in the transport of the ovum from the ovaries to the body of the uterus. The fallopian tubes are also referred to as the uterine tubes or the oviducts. This article will talk about the anatomy, histology, embryology and function of the fallopian tubes followed by any relevant clinical pathology.
Location & Trajectory
The two fallopian tubes are about 10 cm long and project from the superior body of the uterus. They are located within the mesosalpinx, a component of the broad ligament of the uterus, and open medially at the superior angle of the uterus. The fallopian tubes extend in a superolateral direction, pass superior and anterior to the ovaries, and open into the peritoneal cavity lateral to them.
The fallopian tubes consist of four main parts, from medial to lateral:
- Intramural (interstitial) part, which is located within the myometrium of the uterus, is 1 cm long and 0.7 mm wide.
- The isthmus, which is a lateral continuation of the intramural part. It is a rounded, muscular part of the fallopian tube. It is 3 cm long and between 1 and 5 mm wide.
- The ampulla, which is longest part of the tube. It has a diameter of 1 cm at its widest point and is 5 cm long. It has a thin wall, a folded luminal surface and fertilisation usually takes place within its lumen.
- The infundibulum, which is the distal end of the tube. It is funnel shaped and opens into the peritoneal cavity at the abdominal ostium. Finger like mucosal projections are attached to the distal end of the infundibulum and are referred to as fimbriae. These fimbriae are 1 mm wide and project over the medial surface of the ovaries. The longest of the fimbriae, the ovarian fimbria, attaches to the superior aspect of each ovary.
The arterial supply of the fallopian tubes involves both the uterine and ovarian arteries. The uterine artery supplies the medial two-thirds of the tube, whilst the lateral third is supplied by the ovarian artery.
The uterine plexus drains the medial two-thirds of the fallopian tubes into the internal iliac vein whereas the pampiniform plexus drains the lateral two-thirds. The pampiniform plexus drains into the ovarian veins, which in turn drain into the renal vein on the left and the inferior vena cava on the right.
Lymph is also drained by both ovarian and uterine vessels, which drain into the para-aortic and internal iliac lymph nodes, respectively.
The fallopian tubes are innervated by both the sympathetic and parasympathetic nervous systems. The sympathetic nerves arise from the spinal segments T10-L2. The parasympathetic nerves that supply the medial half of the tube are derived from the pelvic splanchnic nerves, whilst the fibres supplying the lateral half of the tube are derived from the vagus nerve.
The walls of the fallopian tubes consist of three main layers:
- the mucosa
- the muscularis
- the serosa
The mucosa is comprised of longitudinal folds, more pronounced at the infundibulum, and is lined by a single layer of tall, columnar epithelium. There are three types of columnar cells within the epithelium: ciliated, non-ciliated secretory and intercalated cells. The ciliated cells are more predominant in the distal portion of the tubes and develop more cilia in the first half of the menstrual cycle. The wave like movement of the cilia aids in the movement of the ovum throughout the fallopian tubes. The longer non-ciliated secretory cells are more active during ovulation and unlike the ciliated cells, are more predominant in the proximal portion of the tubes. These cells secrete a fluid that is propelled with the ovum towards the uterus, by the cilia. The secretion provides a nutrient for the fertilised ovum and also aids in capacitation, a maturation step, of the spermatozoa. Post menopause, the epithelium decreases in height due to a reduction in the number of ciliated cells.
The muscularis is arranged into two layers: an inner circular layer and an outer longitudinal layer. Innervation of these layers results in peristaltic contractions of the fallopian tubes, which assist in propulsion of the fertilised ovum.
The fallopian tubes develop from the paramesonephric or Müllerian ducts. These ducts are derived from the mesoderm, the middle layer of one of the three primary germ layers in the embryo. The other two layers are the ectoderm and the endoderm. The tubes are derived from the superior vertical and middle horizontal aspects of the duct and undergo elongation and coiling to form the fully developed fallopian tubes.
The fallopian tubes are involved in the transport of the ovum from the ovary to the uterus. This is aided by the peristaltic contractions of the muscular layers of the tubes and by the wave-like movement of the ciliated cells. During ovulation, the fimbriae swell which aids the movement of the released oocyte from the ovary to the fallopian tubes. The spermatozoa travel within the tubes towards the ovum and fertilisation usually occurs within the ampulla. Once fertilisation takes place, the tubes also provide nourishment for the fertilised ovum.